26 Pediatric Multislice Com put ed Tomography of the Chest

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CONTENTS

26.1 Introduction 375 26.2 Patient Preparation 375 26.2.1 Sedation 376

26.2.1.1 Pre-sedation Preparation 376

26.2.1.2 Parenteral Sedation Drugs and Techniques 376 26.2.2 Intravenous Contrast Medium 376

26.3 Imaging Techniques 376 26.3.1 CT Protocol 377

26.4 Reconstruction Techniques 378 26.5 Clinical Applications: Chest 378 26.6 Evaluation Of Pulmonary

Metastases (Pro to col 1) 378 26.6.1 Metastases 378

26.6.2 Other Focal Lung Nodules 378 26.7 Congenital Lung

Anomalies (Protocols 1 and 2) 379 26.7.1 Anomalies with Normal Vasculature 379 26.7.1.1 Congenital Lobar Emphysema 379 26.7.1.2 Cystic Adenomatoid Malformation 379 26.7.1.3 Bronchial Atresia 379

26.7.2 Anomalies with Abnormal Vasculature 380 26.7.2.1 Bronchopulmonary Sequestration 380 26.7.2.2 Hypogenetic Lung Syndrome 380 26.7.2.3 Pulmonary Arteriovenous Malformation (AVM) 380

26.8 Mediastinal Mass Evaluation (Protocol 1) 381 26.8.1 Anterior Mediastinal Masses 381

26.8.1.1 Lymphoma 382 26.8.1.2 Thymic Hyperplasia 383 26.8.1.3 Germ Cell Tumors 383 26.8.1.4 Cystic Hygroma 383

26.8.2 Middle Mediastinal Masses 383 26.8.2.1 Bronchopulmonary Foregut Cysts 383 26.8.2.2 Lymphadenopathy 384

26.8.3 Posterior Mediastinal Masses 384 26.8.3.1 Neurogenic Tumors 384 26.9 Vascular Assessment

(CT Angiography) (Protocol 2) 384 26.9.1 Congenital Heart Disease 385 26.9.2 Pulmonary Arteries and Vein 385 26.9.2.1 Pulmonary Arteries 385 26.9.2.2 Pulmonary Veins 386

M. J. Siegel, MD

Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 South Kingshighway Blvd., St. Louis, MO 63110, USA

26.9.3 Aortic Anomalies 386 26.9.3.1 Vascular Rings 387

26.9.3.2 Non-valvar Stenosis of the Aorta 387 26.9.3.3 Aortic Aneurysms and Dissections 389 26.9.4 Systemic Veins 389

26.10 Evaluation of the Airway (Protocol 3) 389 26.10.1 Central Airway Disease 389

26.10.2 Peripheral Airway Disease 390 26.11 Diffuse Lung Disease (Protocol 4) 391 26.12 Chest Wall 392

26.13 Summary 392

References 393

26.1 Introduction

In the early 1980 s the introduction of single-slice helical CT into clinical radiology dramatically im proved the diagnosis of thoracic diseases in chil- dren. The introduction of multislice CT has again ad vanced diagnostic imaging of the pediatric chest.

The beneﬁ ts of multislice CT– improved temporal and spatial resolution, greater anatomic coverage, optimal contrast enhancement, and higher quality three-dimensional renderings– have practical ap pli - ca tions for virtually the entire spectrum of tho rac ic disease. This chapter addresses the areas in which multislice CT has already proved of value in the pe di at ric chest. The technical factors for op ti miz ing the CT examination also are reviewed.

26.2 Patient Preparation

Pediatric patients have several inherent problems that are not present in adults, in particular patient motion, small body size, and lack of perivisceral fat.

These problems can be minimized or eliminated by appropriate use of sedation and oral and intravenous contrast medium.

scho_26-Siegel.ind 375 11.10.2003, 13:16:49 Uhr

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26.2.1 Sedation

As the speed of CT increases, the need for sedation in the pediatric age group decreases (Kaste et al. 1997;

White 1995; Pappas et al. 2000). Although the fre- quen cy has diminished, sedation has not been elim- i nat ed. Sedation will likely still be required for some infants and children 5 years of age and younger to prevent motion artifacts during scanning. Children older than 5 years of age generally will cooperate after verbal reassurance and explanation of the pro ce dure and will not need immobilization or sedation.

Standards of care for sedation are based on rec- om men da tions from the Committee on Drugs, Amer i can Academy of Pediatrics (AAP) (1992) and the Amer i can Society of An es the s- i ol o gists (ASA) Task Force (1996). Sedation for im ag ing examinations is nearly always conscious se da tion. Conscious se da tion is deﬁ ned as a mini- mally depressed level of con scious ness that retains the pa tient’s abilities to main tain a patent airway, in de pen dent ly and con tin u ous ly, and respond appro- priately to physical stimulation and/or verbal com- mand.

26.2.1.1 Pre-sedation Preparation

All patients need to be screened for past and cur- rent illness prior to receiving sedation. This evalua- tion includes (a) a review of past health history and pre vi ous hospitalizations; (b) review of systems; (c) physical examination; and (d) assessment of baseline vital signs (temperature, pulse, respiratory rate, and blood pressure), weight, level of consciousness and motor function.

As part of the preparation process, intravenous access should be obtained, and preparatory guide- lines appropriate to sedation, particularly oral and solid intake status, reviewed. Aspiration is a major clinical concern in sedated children and NPO (non per os or “nothing by mouth”) guidelines should be as stringent as those used for general anesthesia.

26.2.1.2 Parenteral Sedation Drugs and Techniques

The sedatives used most widely for CT are oral chlo- ral hydrate and intravenous pentobarbital sodium.

Oral chloral hydrate (Pharmaceutical Associates, Inc., Greenville, S.C.) is the drug of choice for chil dren younger than 18 months. It is given in a dose of 50

to 100 mg/kg, with a maximum dosage of 2,000 mg.

Onset of action is usually within 20 to 30 min.

In tra ve nous pentobarbital (Nembutal, Abbot Lab o - ra to ries, North Chicago, IL) is preferred in children 18 months of age and older. Intravenous pentobarbi- tal, up to 6 mg/kg, with a maximum dose of 200 mg, is injected slowly in aliquots, starting at 2–3 mg/kg, and is titrated against the patient’s response. Onset of action is usually within 5 to 10 minutes.

Regardless of the choice of drug, the use of par- enter al sedation requires personnel experienced in maintaining adequate cardiorespiratory support during and after the examination. Intravenous ac cess must be continuously maintained and con tin u ous monitoring of vital signs must be performed and recorded.

26.2.2 Intravenous Contrast Medium

Nearly all CT examinations of the chest are per- formed with administration of intravenous contrast material. An intravenous line should be in place be fore the child arrives in the CT suite. This reduces patient agitation that otherwise would be associated with a venipuncture performed immediately prior to administration of contrast material and thus in creas es patient cooperation. The largest gauge can nu la that can be placed is recommended.

26.3 Imaging Techniques

Prior to initiation of scanning, decisions must be made about the anatomic coverage required to an swer the clinical question, the protocol for contrast administration, and the CT acquisition parameters.

In general, the anatomic coverage should extend from just above the thoracic inlet to 1 to 2 cm below the diaphragm. A greater degree of coverage to in clude the upper abdomen may be warranted oc ca - sion al ly, particularly in the setting of assessment of sequestration or aneurysm.

Contrast medium may be administered by hand injection or a mechanical injector (Kaste and Young 1995; Siegel 1999). Hand injections are used when the intravenous access is via a periph- eral vein placed in the dorsum of the hand or foot.

Power in jec tors are used when a 22-gauge or larger

cannula can be placed in an antecubital vein. The

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injection of contrast in order to minimize the risk of contrast extravasation Power injection through a central venous catheter or a 24 gauge catheter has been shown to be safe, pro vid ed that there is proper intravascular positioning of the access line, verifi ed by the unimpeded return of blood and the unim- peded delivery of a saline fl ush (Kaste and Young 1995; Herts et al. 2001) and the rate of injection is slow (1 ml/sec). The ben e fi t of power injection is the uniformity of contrast delivery which allows for maximal enhancement. The complication rates for manual and power in jec tions are similar (<0.4%), provided that the catheter is positioned prop er ly and functions well (Herts et al. 2001). The iodinated contrast material should be nonionic (Co han et al.

1996; Stockberger et al. 1998) and ad min is tered in a volume of 2mL/kg (not to exceed 125 mL).

The ﬁ nal and crucial step for optimizing delivery of the contrast medium is the determination of the scan delay time after the initiation of the contrast medium bolus. In general, a 20 to 30 second delay is sufﬁ cient for routine chest CT examinations (i.e., tu mor staging, evaluation of a mediastinal or pul- mo nary mass, trauma). The shorter delays (20 s) are used in neonates and infants (under 2 years of age), who have higher cardiac output, with longer delay times used in older children and adolescents. For CT angiography (i.e., evaluation of cardiovascular anom a lies, sequestration, arteriovenous mal for - ma tion, and hypogenetic lung), a 12 to 15 second scan delay after the start of the contrast administration produces excellent vascular enhancement in patients under 2 years of age. A 20 to 25 second delay is used in older children.

Because of the additional radiation exposure, un en hanced scans are not obtained routinely prior to contrast administration. They are indicated when as sess ing stent grafts and dissections. In the as sess ment of the former, they help to identify perigraft calciﬁ cations which can mimic a leak on contrast-enhanced scans. In the setting of dissection, un en hanced sections are useful for localizing high at ten u a tion hematoma in the false lumen.

Alternatively, a semi-automated bolus-track- ing method can be used to optimize contrast en hance ment. This method allows continuous moni- toring of the attenuation within a large target vessel (e.g., aor ta or pulmonary artery) by use of a series of

has proven particularly useful in CT angiography.

26.3.1 CT Protocol

For CT examinations performed with a four detec- tor row scanner with an adaptive array design, a nom i nal section (collimator) thickness of 2.5 mm coupled with a table speed of 15 to 20 mm per rota- tion (pitch of 1.5 to 2.0) is adequate. A 1.0 mm col- limation thickness may be of value when a detailed evaluation of small vessels is indicated. For examina- tions per formed with a 16 detector row scanner, the col li ma tion is 1.5 with a table speed of 24 to 36 mm per rotation. A 2.0 to 5.0 mm effective slice thickness is used for viewing thoracic structures.

The CT study should be performed with a single breath hold whenever possible. This can usually be done in children older than 5 or 6 years of age. If breath-holding is not possible, scanning should be performed during quiet respiration.

For the vast majority of thoracic CT studies in chil dren, a single phase study in the arterial phase is sufﬁ cient. However, for evaluation of stent-graft re pair of coarctation, a second set of images, 60 to 70 seconds after the initiation of the contrast injection, can be important to assess for endoleak.

Finally adjustments in tube current must be made in pediatric patients to save radiation exposure (Don nel ly et al. 2001; Haaga 2001; Lucaya et al.

2000; Patterson et al. 2001; Rogalla et al. 1999;

Slovis 2002) (Table 26.1). Because children are more ra di osen si tive than adults to the same organ dose and because they have a longer life span, a potential for de vel op ment of radiation-included malignancies exists. CT should be performed with parameters which pro vide acceptable image quality and the low- est pos si ble radiation exposure. We typically use the lowest possible mil li am per age (mA) and kilovoltage (kV). In patients with smaller body habitus, stud- ies can be performed with 80KV, which lowers the ra di a tion dose to the patient (compared to the stan- dard 120 kV protocols) by a factor of approximately 30%. A high er kV (100 to 120) will be needed in chil- dren with large body habitus.

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26.4 Reconstruction Techniques

When multiplanar or 3D imaging is contemplated, the 2.5 mm and 1.5 mm thick volumetric data are reconstructed with a section thickness of 3 and 2 mm respectively and an interval of 1 to 2 mm. A standard reconstruction algorithm usually sufﬁ ces for routine CT ex am i na tions and CT angiograms, while a high resolution (bone) algorithm is best for examinations of the air way and diffuse lung disease.

A detailed description of the two- and three- di men sion al reconstruction techniques is beyond the scope of this chapter. In general, multipla- nar ref or ma tions and 3D volume renderings are most useful in the assessment of the mediasti- nal great vessels and central airways. Thick-slab maximum and min i mum intensity projections may be useful in eval u a tion of small airway or vessel disease. A more de tailed discussion of multiplanar reformation and three-dimen- sional reconstruction techniques can be found elsewhere in this textbook and in the lit er a ture (Boiselle et al. 2002; Cody 2002; Lawler and Fish man 2001; Ravenel et al. 2001; Ruben 2000).

26.5 Clinical Applications: Chest

The cross-sectional and 3D CT images are helpful in detecting or clarifying abnormalities in the lungs, mediastinum, chest wall and peridiaphragmatic re gions. The information provided by these techniques can directly affect treatment or aid in determining the prognosis of a patient.

The common clinical applications for CT of the pediatric chest are: a) oncologic screening (eval- u a tion of lung metastases); b) congenital lung anom a lies, c) mediastinal masses; d) cardiovascular

anom a lies; e) airway disease; f) diffuse lung disease, and g) complex chest wall abnormalities.

26.6 Evaluation Of Pulmonary Metastases (Pro to col 1)

26.6.1 Metastases

CT is a valuable technique for detection of pul- mo nary metastases in patients with known ma lig - nan cies with a high propensity for lung dissemina- tion, such as Wilms’ tumor, osteogenic sarcoma, and rhab domy o sa r co ma. Demonstration of one or more pul mo nary nodules in such patients, or documenta- tion of additional nodules in a patient with an appar- ent solitary metastasis for whom surgery is planned, may be critical to treatment planning. In the ﬁ rst instance, such detection may lead to additional treat- ment (surgery, chemotherapy, or radiation), whereas in the latter setting, demonstration of several met a - stat ic nodules may negate surgical plans.

The temporal and spatial resolution afforded by CT improves the detection and characterization of pulmonary nodules. The use of thin collimation al lows retrospective reconstructions to be obtained through suspected nodules without the need for res can ning, which decreases radiation dose and op ti miz es the characterization of focal lesions (Remy-Jar din et al. 1993; Wright et al. 1996).

26.6.2 Other Focal Lung Nodules

Other causes of nodular lung lesions, besides me tas- tas es, include granuloma, opportunistic in fec tions, lymphoproliferative disorders, in tra pul mo nary lymph node, and some of the congenital anom a lies (Fig. 26.1). Congenital lesions, such as bron chi al atre- sia or those with abnormal vessels (ar te ri o venous malformation or pulmonary varix), can be diagnosed conﬁ dently with CT. In other instances, clinical his- tory or a repeat CT after waiting 6 to 8 weeks may needed before a speciﬁ c diagnosis can be made. In a patient with a primary neoplasm, an in crease in number or size of nodules can be assumed to repre- sent evidence of metastatic disease.

Table 26.1. Chest CT Acquisitions Factors

Weight (Kg) mA kV

<15 25 80

16–24 30 80

25–34 45 80

35–44 75 80

45–54 90–100 100–120

>54 120 or > 100–120

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26.7 Congenital Lung Anomalies

(Protocols 1 and 2)

Congenital lung anomalies include a variety of con- di tions involving the pul mo nary parenchyma, the pulmonary vas cu la ture, or a combination of both.

Be cause these conditions are associated with either a parenchymal lesion or anom a lous vessels, they are well suited for evaluation by CT scanning (Siegel and Siegel 1999a; Gupta et al. 2002).

26.7.1 Anomalies with Normal Vasculature

Congenital lobar emphysema, cystic adenomatoid malformation, and bronchial atresia are anomalies resulting from abnormal bronchial development. The role of CT is to conﬁ rm the diagnosis and to deter- mine the extent of abnormality in patients in whom surgery is contemplated.

26.7.1.1 Congenital Lobar Emphysema

Congenital lobar emphysema is characterized by hyperinfl ation of a lobe. The CT fi ndings are an over in - fl ated lobe with attenuated vascularity, com pres sion of ipsilateral adjacent lobes, and mediastinal shift to the opposite side. The left upper lobe is in volved in about 45% of cases, the right middle lobe in 30%, the right upper lobe in 20%, and two lobes in 5% of cases.

26.7.1.2 Cystic Adenomatoid Malformation

Cystic adenomatoid malformation is characterized by an overgrowth of distal bronchial tissue that re sults in the formation of a cystic mass rather than normal alveoli. Three types of cystic adenomatoid malformation have been described on pathologic examination: Type I (50% of cases) contains a single or multiple large cysts (>2 cm in diameter); type II (40%) contains multiple small cysts (1 to 20 mm in diameter) ; type III (10%) is a solid lesion to visual inspection, but it contains tiny cysts microscopi- cally. The anomaly occurs with equal frequency in both lungs, although there is a slight upper lobe pre dom i nance. On CT, cystic adenomatoid malfor- mation appears as a parenchymal mass that may be pre dom i nant ly cystic or solid or contain an admixture of cystic and solid components (Siegel and Siegel 1999a; Kim et al. 1997) (Fig. 26.2). Cystic ad e nom a toid mal for ma tion can occur in association with se ques tra tion.

26.7.1.3 Bronchial Atresia

Bronchial atresia results from abnormal de vel - op ment of a segmental or subsegmental bronchus.

CT features of bronchial atresia include overaer- ated lung distal to the atresia and a round, ovoid or branch ing density near the hilum, represent- ing mu coid impaction just beyond the atretic bronchus.

Fig. 26.1. Pulmonary nodules. a: Invasive aspergillosis. CT scan at lung window setting shows a well-circumscribed nod ule sur- rounded by hazy opaque inﬁ ltrate (halo sign) in the right upper lobe. b: Arteriovenous malformation. CT scan shown at soft-tissue setting shows a well-circumscribed en hanc ing nodule (arrow) in the right upper lobe

a b

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26.7.2 Anomalies with Abnormal Vasculature

Sequestration, hypogenetic lung syndrome, and ar te ri o venous malformation (AVM) are congenital anom a lies with abnormal vasculature.

26.7.2.1 Bronchopulmonary Sequestration

Bronchopulmonary sequestration is a congenital mass of pulmonary tissue that has no normal con-

nec tion with the tracheobronchial tree and is sup- plied by an anomalous artery, usually arising from the aorta. When the sequestered lung is conﬁ ned within the normal visceral pleura and has venous drainage to the pulmonary veins, it is termed con- gen i tal or intralobar (Frazier et al. 1997). The se ques tered lung is termed acquired or extralobar when it has its own pleura and venous drainage to systemic veins.

CT scanning after an injection of contrast ma te ri al demonstrates opaciﬁ cation of the anomalous ves sel immediately following peak aortic enhancement (Frazier et al. 1997; Ko et al. 2000) (Fig. 26.3). The anom a lous vessel usually arises from the aorta, but upper abdominal vessels can be a source of the ar te ri al supply. The CT appearance of the pulmonary pa ren chy ma depends on whether or not the se ques - tered lung is aerated. When the sequestration com- mu ni cates with the remainder of the lung, usu al ly after being infected, it appears cystic; a se ques tra tion that does not communicate appears as a ho mo - ge neous density, usually in the posterior portion of the lower lobe.

26.7.2.2 Hypogenetic Lung Syndrome

Hypogenetic lung, also known as venolobar or scimitar syndrome, refers to the combination of a small lung, which is nearly al ways on the right, and anomalous pulmonary venous. Other ﬁ ndings include a corresponding small pulmonary artery and ipsilateral me di as ti nal displacement (Woodring et al. 1994; Zwetsch et al. 1995). The anomalous return is usually into the inferior vena cava, although it may enter the suprahepatic portion of the in fe ri or vena cava, the hepatic veins, portal veins, azygous vein or right atrium. Associated anom a lies include sys tem ic arterial supply to the hy po ge net ic lung and horse- shoe lung. Horseshoe lung is a rare anomaly in which the posterobasal seg ments of both lungs are fused behind the peri car dial sac.

26.7.2.3 Pulmonary Arteriovenous Malformation (AVM)

Pulmonary AVM is characterized by a direct com- mu ni ca tion between a pulmonary artery and vein with out an intervening capillary bed. At CT, AVMs appear as rounded or lobular masses with rapid en hance ment and washout after intravenous contrast me di um administration (Lawler and Fishman 2002;

Hoff man et al. 2000; Remy et al. 1994) (Fig. 26.4).

Fig. 26.2. Cystic adenomatoid malformation. a: Axial image at mediastinal windows shows a predominantly fl uid-fi lled mass in the right lower lobe. Some-air-fi lled areas are also present.

b: A scan at a more caudal level with lung windows shows a complex mass with several air-ﬁ lled cysts

a

b

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anomaly can occur in isolation or with Rendu-Osler- Weber disease.

26.8 Mediastinal Mass Evaluation (Protocol 1)

A widened mediastinum in infants and chil- dren of ten is due to a mass lesion (Bower and Kiesewet ter 1996; Merten 1992; Meza et al. 1993).

The role of CT in the evaluation of mediastinal and lung mass es is lesion characterization and deﬁ nition of extent. In general, axial images alone can provide this in for ma tion. The use of multiplanar reforma- tions in coronal, sagittal, and oblique planes can provide in for ma tion about the longitudinal extent of disease, which can be valuable in patient manage- ment, par tic u lar ly in planning surgical and radiation therapy.

CT appearances of the most common me di as ti nal masses in children are discussed below.

26.8.1 Anterior Mediastinal Masses

Lymphoma, thymic hyperplasia, teratoma, and cystic hygroma are the most common anterior mediastinal masses in children. Rarer causes of anterior me di - as ti nal masses include thymoma, an enlarged thy- roid, thymolipoma, lipoblastoma, and thymic cysts.

Fig. 26.3. Intralobar pulmonary sequestration. A: Axial con trast-enhanced CT section demonstrates a vessel (ar row heads) aris- ing laterally from the descending thoracic aorta and extending to an area of left lower lobe opacity. B: Three-dimensional volume rendering shows the feeding artery (arrow) arising from the aorta and extending to the lower lobe sequestration. Drainage was via a pulmonary, which entered the left atrium

a b

Fig. 26.4. Pulmonary arteriovenous malformation. 3D volume rendering. The feeding artery (arrow) originates from the right lower lobe artery. The draining vein (ar row head) drains into the right inferior pulmonary vein

En hance ment typically occurs immediately after en hance ment of the right ventricle. Axial images can establish the diagnosis of a vascular ring, but 3D reconstructions are of value in demonstrating the precise anatomy of the malformation, including the number of feeding arteries and draining veins, which is critical information for treatment planning. This

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26.8.1.1 Lymphoma

Lymphoma, including Hodgkin’s disease and non- Hodgkin’s lymphoma, is the most common cause of an anterior mediastinal mass. Approximately 65% of pediatric patients with Hodgkin disease have in tra- tho rac ic involvement at clinical presentation, and the superior mediastinal nodes and/or thymus are involved in almost all cases (>95%) (Hudson and Donaldson 1997). Additional sites of involvement are the lung parenchyma (10%) and pleura (10%).

About 40% of pediatric patients with non-Hodgkin lym pho ma have chest disease at diagnosis, and only 50% of this disease involves the superior me di asti num.

Other common sites of involvement in non-Hodgkin’s lymphoma are the hilar and subcarinal node. The frequency of parenchymal and pleural involvement in non-Hodgkin’s lymphoma is about the same as in Hodgkin’s disease (Hammrick-Turn er et al. 1994).

Lymphomatous masses in Hodgkin disease are most common in the anterior mediastinum and re ﬂ ect either inﬁ ltration and enlargement of the thy mus or lymphadenopathy. The enlarged thymus has a quad- rilateral shape with convex, lobular lateral bor ders (Siegel and Siegel 1999b; Siegel 1993) (Fig. 26.5).

The attenuation of the lymphomatous or gan is equal to that of soft tissue. Additional ﬁ ndings include medi- astinal or hilar lymph node en large ment, airway nar- rowing and compression of vas cu lar structures.

Lymphadenopathy is the other common in tratho - rac ic manifestation of lymphoma. The appearance varies from mildly enlarged nodes in a single area to large conglomerate soft tissue masses in multiple re gions. Typically, the enlarged nodes have well- de ﬁ ned margins and show little enhancement after

Protocol 1

INDICATION: Standard Lung/Mediastinum

(Oncologic staging, detection of metastases, characterization of mediastinal or pulmonary mass, eval u a tion of trauma)

Extent Lung apices to caudal bases

Scanner settings: kVp: 80; mA: lowest pos si ble based on patient weight Detector collimation 2.5 mm for 4-row scanner

1.5 mm for 15-row scanner

Table speed (Pitch) 15–20 mm/rotation (1.5–2) for 4-row scanner 24–36 mm/rotation for 16-row scanner Slice thickness 3–5 mm for 4-row scanner

2–5 mm for 16-row scanner IV Contrast Nonionic 280–320 mg iodine/mL

Contrast volume 2 mL/kg (maximum of 4 mL/kg or125 mL, whichever is lower) Contrast injection rate ** Hand injection: rapid push bolus

Power injector:

22 gauge: 1.5 –2.0 mL/sec 20 gauge: 2.0 –3.0 mL/sec Scan delay 20 to 30 s

Miscellaneous 1. If the child is sedated or uncooperative, CT scans are obtained at quite breathing.

2. Contrast medium used at discretion of radiologist in the evaluation of metastases.

Routinely given for evaluation of mediastinal and pulmonary masses and trauma 3. Higher kVp (100 to 120) may be needed in larger patients (>50 kg).

4. Use a standard reconstruction algorithm.

Fig. 26.5. Thymic Hodgkin’s disease. A large anterior me di - as ti nal mass, representing massive inﬁ ltration of the thymus by lymphoma, displaces the carina (arrow) posteriorly. The su pe ri or vena cava (S) is also compressed. Concomitant en large ment of right paratracheal lymph nodes is present. The tumor extends posteriorly to the left paraspinal area and there is a left pleural effusion. Because most mediastinal masses are large, axial images sufﬁ ce for diagnosis. Multiplanar images can be useful to show longitudinal tumor extent.

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26.8.1.2 Thymic Hyperplasia

Thymic hyperplasia is another cause of diffuse thy- mic enlargement. In childhood, it has been as so ci at ed with myasthenia gravis, red cell aplasia, hy per thy - roid ism, but the most frequent cause is rebound hyperplasia. Rebound hyperplasia may be observed during the course of chemotherapy or after the completion of therapy. On CT, hyperplasia appears as diffuse en large ment of the thymus with preservation of the normal triangular shape. The attenuation value of the hyperplastic thymus is similar to that of the nor mal organ. It is the absence of other active disease and a gradual decrease in size of the thymus on serial CT scans that supports the diagnosis of rebound hyperplasia as the cause of thymic enlargement.

26.8.1.3 Germ Cell Tumors

Germ cell tumors are the most common cause of a fat-containing mediastinal mass in children. They are derived from one or more of the three embryonic germ cell layers and usually arise in the thymus.

Approximately 90% are benign and histologically are either dermoid cysts (containing only ectoder- mal elements) or teratomas (containing tissue from all three germinal layers). On CT, both lesions are well-defi ned, thick-walled, predominantly cystic (fl uid-fi lled) masses containing a variable admixture of tissues: calcium, fat, and soft tissue. A fat-fl uid level occasionally can be seen within these tumors.

A malignant teratoma generally appears as a poor ly defi ned, predominantly soft tissue mass, some times containing calcifi cation and fat. Local in fi l tra tion into the adjacent mediastinum with en case ment or inva- sion of mediastinal vessels or air ways also is frequent.

26.8.1.4 Cystic Hygroma

Cystic hygromas are lymphogenous cysts that occur in the antero-superior mediastinum and are almost always inferior extensions of cervical hygromas. The CT appearance is that of a thin-walled, mul tiloc u- lat ed mass of near-water attenuation value. The sur-

26.8.2 Middle Mediastinal Masses

The frequent causes of middle mediastinal masses are congenital foregut cysts and lymph node en large- ment.

26.8.2.1 Bronchopulmonary Foregut Cysts

Bronchopulmonary foregut malformations include bronchogenic, enteric and neurenteric cysts (Siegel and Siegel 1999b; Haddon and Bowen 1991). Bron- chogen ic cysts are lined by respiratory ep i the li um, and most are located in the subcarinal or right paratra che al regions. Enteric cysts, also known as esophageal duplications are lined by gastrointestinal mucosa and usually are located close to or within the esophageal wall. Neurenteric cysts are posterior me di as ti nal lesions that are connected to the menin- ges through a midline defect in one or more vertebral bodies and are lined by gastrointestinal epithelium.

CT ﬁ ndings of foregut cysts include a non- en hanc ing round or tubular mass with well-deﬁ ned margins and thin or imperceptible walls (Fig. 26.6).

The cyst contents usually are homogeneous and of

Fig. 26.6. Enteric cyst. Axial contrast-enhanced CT shows a well- deﬁ ned, homogeneous water-attenuation mass (ar row head) ﬁ ll- ing the azygoesophageal recess

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near-water attenuation, reﬂ ecting their serous na ture.

Some foregut cysts will have higher attenuation values because the contents contain proteinaceous ﬂ uid, hemorrhage, mucus, or calcium.

26.8.2.2 Lymphadenopathy

Lymph node enlargement, as a cause of a middle mediastinal mass, is usually caused by lymphoma or granulomatous disease. On CT, adenopathy can ap pear as discrete soft tissue masses, or as a single soft tissue mass with ill deﬁ ned margins. Calciﬁ ca- tion within lymph nodes suggests old granulomatous dis ease, such as histoplasmosis or tuberculosis. Low at ten u a tion areas suggest tuberculosis.

26.8.3 Posterior Mediastinal Masses

26.8.3.1 Neurogenic Tumors

Neurogenic tumors are the most common cause of a posterior mediastinal mass. Neuroblastoma and gan- gli o n euro blas to ma are more common in infants and children, while ganglioneuroma, neuroﬁ broma and schwannoma increase in frequency in ad o les cents and adults. Rarer causes of posterior me di as ti nal masses in children include paraspinal abscess, lymphoma, neur- enteric cyst, lateral meningocele, and extramedullary hematopoiesis.

On CT, ganglion cell tumors appear as fusiform or elongated paraspinal masses, extending over the length of several vertebral bodies (Siegel and Sie gel 1999b). They are of soft tissue attenuation and con tain calciﬁ cations in up to 50% of cases (Fig. 26.7).

Nerve root tumors tend to be smaller, spher i cal, and occur near the junction of a vertebral body with an adjacent rib. Both types of tumors may cause pres sure erosion of a rib. Because of their or i gin from neural tissue, neurogenic tumors have a ten den cy to invade the spinal canal. Intraspinal ex ten sion is ex tra du r al in location, displacing and oc ca sion al ly com press ing the cord. Identiﬁ cation of in traspi nal invasion is important because affected pa tients re quire radiation therapy or a laminectomy prior to tumor debulking.

26.9 Vascular Assessment (CT Angiography) (Protocol 2)

The evolution of multislice CT has led to a changing role for CT angiography in the evaluation of car dio - vas cu lar anomalies in children. CT angiography can clearly demonstrate the morphology of the pul mo nary vessels and aorta and thus, it has gained in creas ing acceptance as an alternative method to MR imaging and conventional catheter angiography in the diagno- sis of vascular anomalies (Hopkins et al. 1996; Katz et al. 1995). An important advantage of CT angiography over MR angiography relates to the short er scan time which means reduction in the need for sedation and the ability to scan extremely ill patients who cannot toler- ate the long imaging times for MR examinations. There is the risk of radiation exposure in CT angiography, but in the critically ill patient the risk of prolonged sedation may be greater than that of radiation. Compared with the radiation dose for angiography, the radiation dose for CT an giog ra phy is at least two to three times less.

While routine axial images are usually suf ﬁ cient for diagnosis, the reconstructed images can pro vide better anatomic detail about anatomic re la tion ships between the great vessels and tra che o bron chi al tree and pro- vide a more reliable as sess ment of airway compromise.

With regard to the as sess ment of vascular narrowing, multiplanar vol ume reformation and 3D reconstruc- tions can aid in the detection of mild coarctations and improve the accuracy of determining the length of coarctation. In addition, these images can aid in the planning of surgery or stent placement.

Fig. 26.7. Posterior mediastinal mass, neuroblastoma. Axial CT scan through the lower thorax shows a large soft tissue tumor (T) in a paravertebral location. The tumor extends around the descending aorta (A). Also seen are bilateral pleu ral effusions

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26.9.1 Congenital Heart Disease

Most congenital and acquired cardiac lesions are evaluable by echocardiography, but CT can be of use when echocardiography provides inadequate in for - ma tion. The major indications for CT in congenital cardiac anomalies include: (a) evaluation of the size and patency of the pulmonary arteries in patients with cyanotic heart disease, such as pulmonary atre sia and tetrology of Fallot, (b) detection of anom a lous origin of the coronary artery (Fig. 26.8), (c) de ter mi na tion of the extracardiac anatomy in patients with complex congeni- tal heart disease (e.g. great ves sel relationships, bronchial collateral vessels, ab dom i nal situs), and (d) evaluation of surgically created systemic-to-pulmonary artery shunts in patients with complex anatomic heart diseases, such as trun cus arteriosus, tetrology of Fallot, hemitruncus, and pulmonary atresia. Vessel anatomy, shunt patency, and the presence of collateral vessel formation are clearly depicted with 3D volume rendering tech niques.

Because multislice CT can be performed rapidly, artifacts from cardiac pulsation are eliminated or minimized. In addition, the use of 3D volume ren- der ing allows for more conﬁ dent depiction of vessels that course obliquely through the imaging planes.

26.9.2 Pulmonary Arteries and Vein

26.9.2.1 Pulmonary Arteries

The two common abnormalities of the pulmonary arteries are the obstructive lesions (i.e., pulmonary artery atresia, stenosis and hypoplasia) and the pul- mo nary sling.

Detector collimation 2.5 mm for 4-row scanner 1.5 mm for 15-row scanner

2–5 mm for 16-row scanner IV Contrast Nonionic 280–320 mg iodine/mL

Contrast volume 2 mL/kg (maximum of 4 mL/kg or150 mL, whichever is lower) Contrast injection rate Hand injection: rapid push bolus

Power injector:

22 gauge: 1.5–2.0mL/sec 20 gauge: 2.0–3.0 mL/sec Scan delay Patient weight <15 kg: 12 to 15 s

Patient weight >15 kg: 20 to 25 s

Miscellaneous 1. If the child is sedated or uncooperative, CT scans are obtained at quite breathing.

2. Higher kVp (100 to 120) may be needed in larger patients (>50 kg).

3. If sequestration is suspected, scanning should extend through the upper abdominal aorta.

4. Precontrast images are not needed for most examinations, but they are used in the evaluation of

endovascular stents.

5. Use standard reconstruction algorithm.

Fig. 26.8. Anomalous origin of the left coronary artery. Three dimensional volume-rendered images. The left coronary ar tery (arrows) originates from the main pulmonary artery (P)

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The role of CT angiography in patients with ob struc tive lesions of the pulmonary artery is to de ter mine the presence, caliber and conﬂ uence of the main pulmonary arteries and the presence and dis tri - bu tion of collateral vessels (Fig. 26.9). Collateral ves- sels can originate from brachiocephalic arteries, the descending thoracic aorta, or the sub di a phrag mat ic aorta. These collateral arteries can anas to mose with intrapulmonary vessels.

brachiocephalic vein, producing a vertical vein that courses lateral to the aortic arch and aor top ul mo nary window. The anomalous right inferior pulmonary vein drains cephalad into the azygous vein or caudal into the subdiaphragmatic inferior vena cava or portal vein, producing a scimitar vein.

26.9.3 Aortic Anomalies

The common anomalies of the aorta are the vascular rings and non–valvar stenotic lesions (coarctation, interrupted arch, supravalvular stenosis). Aneurysm formation and dissection are rare in children.

Fig. 26.9. Pulmonary stenosis with a failed right Blalock- Taussig shunt. Coronal volume rendered image demonstrates multiple transpleural collateral vessels arising from a dilated, tortuous right mammary (internal thoracic) artery (arrows)

Fig. 26.10. Partial anomalous venous return. A: Axial CT scan at the level of the superior mediastinum shows part of the anomalous pulmonary vein draining the right upper lobe.

B: 3D volume rendered image, viewed from behind, shows the anomalous vessel entering the superior vena cava (S).

Arrow=anomalous vein

a

b

In patients with pulmonary sling, the left pul mo nary artery originates from the right pulmonary ar tery and crosses the mediastinum, extending be tween the tra- chea and esophagus to reach the left hi lum. Patients typically present with respiratory symp toms due to compression of the airway by the left pulmonary artery or associated stenosis of the trachea or main bronchi.

26.9.2.2 Pulmonary Veins

Partial anomalous return is the most common ab nor -

mal i ty of the pulmonary veins. Anomalous drain age

of the pulmonary veins can occur in iso la tion or with

hypogenetic lung syndrome (Fig. 26.10). The anoma-

lous drainage commonly involves the left superior

and right inferior pulmonary veins. The anomalous

left superior pulmonary vein drains into the left

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of the arch encircling the trachea and esophagus. The diagnosis of a vascular ring is usually suggested on conventional chest radiography. CT is used to deﬁ ne the anatomy for surgical planning. Axial images can establish the diagnosis of a vascular ring, but coro- nal images are of value in dem on strat ing the precise anatomy of the rings and their re la tion ship to adja- cent structures.

The common symptomatic vascular rings are the double aortic arch and the right aortic arch with an aberrant left subclavian artery. In double aortic arch, there are two aortic arches, both of which arise from a single ascending aorta. Each arch gives rise to a sub cla vi an and carotid artery, before uniting to form a single descending aorta. The right arch tends to be higher and larger than the left (Fig. 26.11). The two components of the arch encircle the trachea and esoph- a gus, resulting in airway compromise or dys ph agia.

Right aortic arches are classiﬁ ed into two major subtypes: the right arch with an aberrant left sub- cla vi an artery and the right arch with mirror-imag- ing branching. The former type is rarely associated with congenital heart disease. In a right aortic arch anom a ly with an aberrant left subclavian artery,

vessel or because the descending aorta compresses the tra chea (Donnelly et al. 2002). On CT, the aber- rant sub cla vi an artery is seen as the last branch vessel to arise from the right aortic arch; it is often dilated at its origin (Fig. 26.12). A right aortic arch with mirror image branching has a high incidence of heart dis ease, but stridor and dysphagia are usually absent because there is not structure posterior to the tra chea of the esophagus.

26.9.3.2 Non-valvar Stenosis of the Aorta

Aortic Coarctation

Coarctation of the aorta refers to a constriction or obliteration of a segment of that vessel. The segment of aorta just distal to the left subclavian artery is the most common site of coarctation. If the coarctation occurs between the left subclavian artery and the ductus arteriosus, it is termed preductal or infantile coarctation. This type may be associated with aortic arch hypoplasia. The second type of coarctation oc curs distal to the ductus arteriosus and is referred to as adult coarctation (Fig. 26.13). In this anomaly, the aortic arch is usually of normal diameter, and col- lat er al vessel formation is common.

Following surgical repair or balloon angioplasty, CT is useful to demonstrate aneurysm or restenosis.

Fig. 26.11. Double aortic arch. Coronal volume rendered im age shows a double arch. R = right arch; L = left arch

Fig. 26.12. Right aortic arch. Axial contrast-enhanced image shows the right arch (A) and aberrant left sub cla vi an artery (arrow) crossing behind the trachea. Mild com pres sion of the right wall of the trachea is seen

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Patients who have had repair of coarctation using prosthetic patches have an approximately 25% risk of developing aneurysms at the coarctation repair site (Bromberg et al. 1989).

Interruption of the Aortic Arch

Interruption of the aortic arch is characterized by complete discontinuity between the ascending and the descending aorta. There are three basic types of inter- rupted arch, which in descending order of fre quen cy are: Type A: interruption of the aortic arch distal to the left subclavian artery, Type B: in ter rup tion of the arch between the left common carotid artery and the left subclavian artery, and Type C: interruption of the arch proximal to the left carotid artery. CT angiog- raphy can demonstrate the in ter rupt ed transverse arch and the patent ductus ar te ri o sus supplying the descending aorta (Fig. 26.14). It is important not to mistake the dilated patent ductus arteriosus for the transverse arch.

Aortic Stenosis

Aortic narrowing can be seen in patients with ar teri tis, such as Takayasu arteritis, and William’s syn drome. Takayasu arteritis is a primary arteritis

of unknown origin that commonly affects the aorta and its major branches as well as the pulmonary artery. William’s syndrome is characterized by the com bi na tion of supravalvar aortic stenosis, peripheral pul mo nary arterial stenosis, mental retardation, and an “elfin facies”. CT angiography can delineate the site and length of the aortic nar- row ing and a thickened arterial wall (Yamada et al. 1998).

Fig. 26.13. Aortic coarctation. Volume ren dered 3D reconstruction demonstrates focal narrowing (ar row) of the proximal descending aorta. Also note the large mammary artery collateral vessel (arrowheads)

Fig. 26.14. Interrupted aortic arch. A Axial CT section in a 2 kg neonate demonstrates a normal caliber proximal aorta (A). The vessel latter and inferior to the aorta is a dilated patent ductus arteriosus (arrowheads). B: Volume-rendered reconstruction shows a markedly hypoplastic trans verse arch (arrowhead) and a large patent ductus ar te ri o sus (PDA) which supplies the distal aorta

a

b

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ciated with predisposing conditions, such as Turner syndrome, aortic coarctation, Marfan’s syn drome (Fig. 26.15), Ehlers-Danlos syndrome, Ka wasa ki’s disease, prior surgery, or trauma.

The diagnosis of aneurysm can be made when the diameter of the aorta is greater than 50% of the nor- mal diameter of the aorta or when the diameter of the proximal descending aorta is 1.5 times the di am e ter of the descending thoracic aorta at the level of the dia- phragm (Fig. 26.15). The CT diagnosis of dis sec tion is based on demonstration of an intimal ﬂ ap (Fig. 26.15).

In general, the true aortic lumen is smaller than the false lumen, has an oval shape, follows the inner curve of the aorta, and contains faster ﬂ owing blood. The false lumen is usually larger than the true lumen, is crescent shaped, follows the outer curve of the aor ta, and contains slower ﬂ owing blood.

26.9.4 Systemic Veins

The common venous anomalies include: duplicated superior vena cava and interruption of the inferior vena cava with azygous/hemiazygous continuation.

A persistent left superior vena cava can occur in the general population, but it is more likely to occur in patients with congenital heart disease. The left su pe ri or vena cava lies lateral to the aortic arch as it descends along the left side of the mediastinum. As it courses inferiorly, it passes lateral to the main pul- mo nary artery and anterior to the left hilum to enter the coronary sinus that wraps around the bottom of the left atrium.

Inferior vena caval interruption results when the suprarenal, infrahepatic segment of the inferior vena cava fails to develop. Blood from the lower half of the body then returns to the heart via persistent sub- car di nal veins, termed the azygos and hemiazygous veins. Azygous and hemiazygous continuation of the inferior vena cava can be an isolated abnormality or it can coexist with congenital heart disease. CT ﬁ nd- ings are dilatation of the azygos arch, the azygos vein, and the superior vena cava caudal to the azygos junc- tion; enlargement of the azygos and hemi az y gous veins in the paraspinal and retrocrural areas; and absence of the suprarenal and intrahepatic por tions of the inferior vena cava.

26.10 Evaluation of the Airway (Protocol 3)

26.10.1 Central Airway Disease

Axial CT images remain the standard for evaluating the central airways. However, multiplanar and 3D reconstructions can provide additional useful in for - ma tion and more precise depiction of tra che o bron chi al abnormalities (Hoppe et al. 2002; Lee et al. 1997; Remy- Jardin et al. 1998a,b; Sorantin et al. 2002).

Axial images are indispensable for assessing ex tralu mi nal disease, including the lung parenchyma and mediastinal structures. Multiplanar ref or - ma tions aid in the detection of mild stenoses and tra che o ma l a cia, provide a more reliable assessment of the extent of narrowing in the craniocaudal di rec tion, and aid in the planning of stent placement or surgery (Boiselle et al. 2002). For the evaluation of tracheo- malacia, scans are acquired at both end-in spi ra tion and end-expiration and then reformatted in coronal and sagittal planes. This technique is lim it ed to coop- erative patients or to patients who are on assisted ventilation. In most uncomplicated cases, 3D recon- structions are of minimal value and only supplement multiplanar ref or ma tions. However, they can help to depict complex congenital airway abnormalities,

Fig. 26.15. Annuloaortic ectasia and dissection secondary to Marfan’s disease. Axial CT scan shows a dilated proximal de scend ing aorta (A) and an intimal ﬂ ap (arrow) in the distal descending aorta, due to an acute dissection

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such as abnormal origins of the bronchi or broncho- esophageal ﬁ stulas, and they can help to improve the detection of subtle airway stenosis (Remy-Jardin et al. 1998a,b). In ad di tion, they can provide information about the shape, length and extent of airway stenosis (Boi selle et al. 2002). Virtual bronchoscopy has a rather limited ap pli ca tion, but it is indicated when there is a high-grade stenosis or large intraluminal tumor. This tech nique allows evaluation of the air- ways be yond the site of stenosis or neoplasm, which oth er wise can be difﬁ cult to visualize by conventional bron cho s co py.

The indications for CT of the pediatric trachea and large bronchi include: evaluation of congenital bronchial anomalies (e.g., accessory bronchi, bron- chi al hypoplasia and atresia (McGuiness et al. 1993;

Al-Nakshabandi et al. 2000), assessment of the ex tent of tracheal stricture (Quint et al. 1995) (Fig. 26.16) or tumor (Fig. 26.17), and detection and conﬁ rmation of tracheomalacia (Fig. 26.18) (Gilke son et al. 2001).

26.10.2 Peripheral Airway Disease

Bronchiolitis obliterans is the most common pe ri- ph er al airway disease in children. It primarily affects the terminal and respiratory bronchioles and is the result of submucosal and peribronchiolar in fl am - ma tion and fi brosis; parenchymal infl ammation is ab sent. Bronchiolectasia with inspissated secretions is another common fi nding at histologic examination.

There are three predominant CT patterns of dis- ease: (a) a tree-in-bud pattern; (b) poorly deﬁ ned centrilobular nodules; and (c) decreased lung at ten u a tion (Aquina et al. 1996; Collins et al.

1998; Lau et al. 1998; Muller and Miller 1995).

Protocol 3

INDICATION: Tracheobronchial tree

(Congenital anomalies; stricture, tumor, tracheomalacia) Extent Vocal cords to mainstem bronchi, just be low carina Scanner settings: kVp:80; mA: lowest possible

Detector collimation 2.5 mm for 4-row scanner 1.5 mm for 15-row scanner

2–5 mm for 16-row scanner Patient Instructions Suspended inspiration Contrast type None

Comments 1. Aim for a single breath hold. Select pitch so that the area of interest can be scanned in a single breath hold in cooperative patients.

2. Use high spatial resolution re con struc tion (bone) algorithm

3. Multiplanar and 3D reconstructions are useful to provide an overview of anatomy for surgical

plan ning.

4. If small airway obstruction or tracheomalacia is suspected, obtain scans in inspiration and expiration 5. If child sedated or uncooperative, CT scans obtained at quiet breathing.

Fig. 26.16. Tracheal stricture secondary to prior intubation.

Coronal multiplanar reformation shows focal narrowing of the proximal airway (arrowheads)

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The de creased lung attenuation represents a com- bination of oligemia and air-trapping (Siegel et al.

(2001); Stern and Frank 1994). This appearance has been termed mo sa ic perfusion or mosaic atten- uation. The pres ence of air trapping can be con- ﬁ rmed by acquisition of images in both inspiration and expiration, either at a single level or through select lung volumes (Fig. 26.19).

lung disease. CT, however, can be useful to better defi ne and characterize an abnormality suspected on con ven tion al chest radiography, especially when the CT examination is performed with high resolu- tion tech nique using 1 mm collimation every 10 to 20 mm. In most instances, axial images suffi ce for diagnosis. Multiplanar and 3D maximum intensity projection (MIP) and minimum intensity projec- tion (minIP) images can help to characterize some diffuse lung diseases. MIP images can increase small nodule de tec tion and help in characterizing the location of centrilobular and peribronchovascular nodules, where as minIP images can improve depic- tion of the lumen of small airways and centrilobular em phy se ma. Recent reports have suggested that auto- mated segmentation techniques may further improve the identifi cation of diffuse lung disease and perhaps aid in the ability to quantify lung volumes and pul- mo nary function (Bankier 1999; Genevois 1996).

The indications for high-resolution CT of the lung parenchyma in children include: (a) detection of dis ease in children who are at increased risk for lung disease (e.g., immunocompromised patients) and who have respiratory symptoms but a normal

Fig. 26.17. Central airway tumor in a young adult following lung transplantation. Coronal 3D volume rendered reconstruction shows a soft-tissue mass (arrowhead) in the right mainstem bronchus. Final diagnosis was post-trans plant lymphoproliferative disease

Fig. 26.18. Tracheomalacia in a 1-month-old girl who had undergone an esophageal pull-through for repair of esoph ageal atresia and who had marked dyspnea on attempts to extubate. The patient was intubated during the CT scan, al low ing images to be obtained in inspiration and expiration. A: CT scan during end inspiration and B: during end ex pi ra tion demonstrates a dilated esophagus (E) and marked col lapse of the intrathoracic trachea (T), consistent with tracheomalacia, which was conﬁ rmed at ﬁ beroptic bron cho s co py

a b

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chest radiograph; (b) determination of the extent, dis tri bu tion, and character of diffuse lung diseases;

(c) lo cal iza tion of abnormal lung for biopsy; and (d) as sess ment of the response to treatment.

26.12 Chest Wall

Multislice CT can also be applied to imaging of the thoracic cage (Pretorius and Fishman 1999). The com plex anatomy of the thoracic cage is particularly well suited to multiplanar and 3 D volume-render- ing imaging. These techniques can be of value in the imaging of a variety of chest wall abnormalities. In particular, they can help in evaluating congenital and postsurgical changes (Fig. 26.20), assessing the re la -

tion ship of peripheral masses to the chest wall and in surgical planning of repair of pectus excavatum deformities

26.13 Summary

In summary, multislice CT is an important non in - va sive tool for imaging the pediatric thorax. The clear delineation of anatomy, the high levels of contrast enhancement, and the continued reﬁ nement of 3D tech niques have increased the applications of CT in chest imaging. Despite the obvious impact that multislice CT has already has on thoracic imaging, it cannot be overstated that attention must be paid to patient preparation and radiation doses.

Protocol 4

INDICATION: Combined Chest/High Resolution CT) (Suspected interstitial disease) Extent Lung apices to caudal bases Scanner settings: kVp: 80; mA: lowest pos si ble Detector collimation 1 mm

Table Speed 10–20 mm

Slice thickness 5 mm for initial survey, 1.25 mm for HRCT Patient Instructions Suspended inspiration

IV Contrast None

Miscellaneous 1. Expiration imaging can be useful to evaluate suspected areas of air trapping.

2. If child sedated or uncooperative, CT scans obtained at quiet breathing.

Fig. 26.19. Bronchiolitis obliterans in a 14-year-old girl after bilateral lung transplantation. a: Axial section through the lower lungs at inspiration shows several areas of mild bron chi al dilatation. b: Scan during expiration shows mosaic at ten u a tion. The lower attenuation areas indicate air trapping and small airway obstruction. Bronchial dilatation is again noted

a b

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