6L.van den Hauwe,J.W.Casselman

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Magnetic Resonance Imaging of the Head and Neck 6

L. van den Hauwe, J. W. Casselman

Contents

6.1 Temporal Bone . . . 174

6.1.1 Introduction . . . 174

6.1.2 Coils and Patient Positioning . . . 174

6.1.3 Sequence Protocol . . . 176

6.1.4 Pathology . . . 180

6.2 Eye and Orbit . . . 180

6.2.4 Pathology . . . 183

6.3 Paranasal Sinuses . . . 185

6.3.4 Pathology . . . 192

6.4 Skull Base . . . 193

6.4.4 Pathology . . . 193

6.5 Nasopharynx and Surrounding Deep Spaces and Parotid Glands . . . 196

6.5.4 Pathology . . . 199

6.5.4.1 Nasopharynx . . . 199

6.5.4.2 Surrounding Spaces . . . 199

6.5.4.3 Parotid Gland . . . 200

6.6 Oropharynx and Oral Cavity . . . 200

6.6.4 Pathology . . . 203

6.7 Larynx and Hypopharynx . . . 203

6.7.4 Pathology . . . 204

6.8 Temporomandibular Joint . . . 204

6.8.4 Pathology . . . 208

Further Reading . . . 208

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6.1

Temporal Bone 6.1.1

Introduction

The external and middle ear are best examined with computed tomography (CT). However, in patients presenting with sensorineural hearing loss (SNHL), vertigo and tinnitus, one must evaluate the inner ear, the internal auditory canal (IAC), the cerebellopontine angle (CPA) and the auditory/vestibular pathways in the brain and brainstem. Only magnetic resonance (MR) imaging is able to visualize all these structures and detect a sufficient amount of pathology in these

patients. MRI also has become the method of choice in the detection and characterization of lesions of the petrous apex (cholesterol granuloma, congenital cho- lesteatoma) and in the diagnosis of meningo(encephalo)coeles in case of defects in the tegmen of the middle ear.

6.1.2

Coils and Patient Positioning

Patients are examined in the supine position with the head firmly fixed in the head coil. Axial images should be centred on the superior border of the external auditory canal. Multiple coronal localizers may be required

Fig. 6.1A,B. Positioning and orientation of the T2- weighted (T2-W) gradient-echo (GRE) slab on the coronal scout view (A) and a transverse spin-echo (SE) T2-weighted image (T2-WI) (B). The internal auditory canal (IAC) is not always easy to visualize on the thick and blurred coronal scout views.

However, the complete inner ear is included in the study if the slab covers the inferior border of the temporal lobes and reaches the level of the jugular foramen and hypoglossal canal inferiorly. The slab can be angulated to correct for skull or positioning asymmetries (A). Transverse T2-WI or T1-WI can be used to verify whether the small field of view (FOV) (95 mm) GRE slab is correctly positioned so that both lateral semicircular canals (arrows) are included in the study (B)

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to correct imperfect positioning (head tilting) or intrin- sic asymmetries of the skull (Fig. 6.1). We prefer a standard circularly polarized head coil, because it allows imaging of both temporal bones simultaneously, and the signal remains homogeneous throughout the image. With this type of coil, even the root-entry zone and brainstem can be assessed. Moreover, the same coil can also be used to acquire a T2-weighted (T2-W) brain

study, which is mandatory in patients with SNHL, vertigo and tinnitus.

Before positioning the patient in the magnet, hearing aids should be removed. Most cochlear implants are incompatible with MRI. In general, modern prostheses used for ossiculoplasty are not a contraindication for MRI.

Fig. 6.2. Brainstem infarction. Thin spin-echo (SE) T2-weighted image of the brainstem in a patient with acute sensorineural hearing loss on the right side. A high signal intensity infarction (black arrows) can be seen at the level of the right cochle- ar nucleus in the lower pons. Notice also the low signal intensity of the myelinated medial longitudi- nal fasciculus on both sides (arrowheads). The IAC is also recognizable (white arrows)

Fig. 6.3A,B. Labyrinthitis. Transverse unenhanced (A) and coronal gadolinium (Gd)-enhanced (B) SE T1-WI through the left membranous labyrinth in a patient with labyrinthitis. A A spontaneous high signal intensity is seen in the vestibule (long white arrow) and represents intra- labyrinthine fluid with a high protein concentration or fluid mixed with blood. The posterior wall of the IAC (arrowheads) and the cochlea (small white arrow) are seen. On the Gd-enhanced image (B), enhancement is observed in the vestibule (long white arrow) and superior semicir- cular canal (small white arrow). The roof of the IAC is indicated by arrowheads. The GE T2-WI (not shown) demonstrated the presence of fluid throughout the left membranous labyrinth

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6.1.3

Sequence Protocol

1. A routine T2-W brain study, with axial scans from the base of the skull to the vertex, should always be performed in order to exclude a sometimes clinically unexpected central cause of SNHL or vertigo (Fig. 6.2).

2. Axial unenhanced spin-echo (SE) T1-weighted images (T1-WI) are needed to detect intrinsically hyperintense lesions, such as schwannoma, lipoma, blood (trauma), cholesterol granuloma or fluid with a high protein concentration. Without these images, it becomes impossible to differentiate enhancement from spontaneous hyperintensities on the gadolin-

ium (Gd)-enhanced T1-WI. An alternative solution is not to acquire unenhanced images routinely to save time and to re-examine the patient the next day whenever an intralabyrinthine enhancement or high signal, occurring in about 2% of studies, is found.

3. A Gd-enhanced T1-W sequence provides the most sensitive images for detecting pathology in the membranous labyrinth, IAC and CPA (Figs. 6.3 and 6.4). It is, therefore, obligatory to obtain this sequence. Intravenous administration of 0.1 mmol/

kg of Gd is sufficient. The axial Gd-enhanced images must be obtained in the same positions (table positions) as the precontrast images so that comparison is possible. Slice thickness of the pre- and postcon- trast T1-WI should not exceed 3 mm; 2-mm thin

Fig. 6.4A,B. Acoustic schwannoma. Transverse 2- mm-thick Gd-enhanced T1-weighted image (T1- WI) (A) and 0.7-mm-thick gradient-echo (GRE) T2-WI (B) in a patient with a schwannoma of the superior vestibular branch of the vestibulocochlear nerve. A A nodular enhancing lesion (black arrows) can be seen in the IAC, but it is impossible to further define the exact position of the lesion on this image. The cochlea (thick white arrow) and vesti- bule (thin white arrow) are noticed. On the thin- section T2-W GRE images (B), the facial nerve (black arrowheads) can be recognized anteriorly in the IAC. A nodular lesion (large black arrow) can be seen in the course of the vestibular branch of the vestibulocochlear nerve (small black arrows).

Notice the cochlea with separate visualization of the scala tympani and scala vestibuli (large white arrow), the vestibule (long white arrow), the lateral (small white arrow) and posterior (white arrow- heads) semicircular canals

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slices are considered state of the art. Slices should be contiguous, i.e., there should be no interslice gap.

The same technique should be applied for coronal images, which can be helpful to confirm doubtful or subtle pathology.

4. T1-WI with fat suppression are particularly useful in the postoperative patient to separate residual/recurrent schwannoma from high signal fatty material used by the surgeon. On Gd-enhanced T1-WI, both have a high signal intensity and can be difficult to differentiate.

5. Gradient-echo (GRE) or turbo spin-echo (TSE) T2- WI are required to evaluate the very small structures of the CPA, the four nerve branches in the IAC, and the fluid inside the membranous labyrinth (Figs. 6.4

and 6.5). It is important to obtain the GRE images prior to the administration of Gd to avoid Gd-inten- sified flow artefacts. When possible, 0.5-mm to 0.7- mm-thick slices should be used; slice thickness should not exceed 1 mm. The slab becomes thinner when submillimetric images are used, and hence, positioning becomes critical in the coronal plane.

High-resolution imaging can be achieved with a 512×512 matrix at the expense of increasing the acquisition time and decreasing the signal-to-noise ratio. Alternatively, we prefer to use a very small field-of-view (FOV) of 95 mm with a 256 matrix, which provides a similar in-plane spatial resolution, but without increasing the acquisition time. In most patients, both inner ears will just fit in a FOV of

Fig. 6.5A,B. Large vestibular aqueduct syndrome.

Transverse 0.7-mm thick GE T2-WI (A) and a para- sagittal reconstruction (B) of the right membra- nous labyrinth, made from these transverse 0.7- mm-thick images, in a patient with a large endolymphatic duct and sac (large vestibular aqueduct syndrome). The patient had sensorineural hearing loss and was, therefore, referred for MRI. An enlarged, fluid-filled endolymphatic sac can be rec- ognized (white arrowheads). The sac is abnormal when the diameter is larger than the diameter of the fluid-filled posterior semicircular canal (long white arrow). Fluid-filled vestibule (V) and cochlea with separate visualization of the two scalas (large white arrow). Facial nerve (black arrowheads), com- mon trunk of the vestibulocochlear nerve (small black arrow) and its more peripheral cochlear (large black arrow) and inferior vestibular (long black arrow) branches (A). The enlarged, fluid- filled endolymphatic sac (white arrowheads) can be followed from the labyrinth to the anterior border of the cerebellum (C). Fluid-filled superior semicir- cular canal (long white arrow) and cochlea (large white arrow). Facial nerve (black arrowhead), coch- lear branch (large black arrow) and vestibular branches (long black arrows) of the vestibulococh- lear nerve, surrounded by cerebrospinal fluid (CSF) in the fundus of the IAC (B)

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95 mm, but accurate positioning is crucial, and it is best to use the thin-section axial unenhanced T1-WI or T2-WI to check whether the GRE slab also covers the outer borders of the lateral semicircular canals.

Only these GRE T2-WI can discriminate high signal intralabyrinthine fluid from low signal intralabyrinthine fibrosis or tumour.

In acoustic neuroma surgery, these T2-WI will allow us to determine the type of surgery to be performed.

If fluid is still present between the schwannoma and the fundus of the ICA, hearing preservation surgery (middle cranial fossa or retrosigmoid approach) is

possible. If no fluid is observed, the surgeon has to remove all the tissue up to the base of the cochlea, leaving the patient deaf. In these patients a less inva- sive translabyrinthine approach is performed. An even more important sign is the signal intensity of the cerebrospinal fluid between the schwannoma and the fundus of the ICA and the signal intensity of the intralabyrinthine fluid. Hearing preservation is achieved four times more often when a normal signal intensity of these fluids is observed (Fig. 6.6).

6. To detect vascular malformations and neurovascular conflicts, 1-mm-thick, high-resolution, time-of-flight

Fig. 6.6A–C. Transverse 0.7-mm-thick GE T2-WI through the right (A) and left (B) inner ear and projection image of all axial images through both inner ears (C). An acoustic schwannoma can be seen in the right internal auditory canal (small white arrows), replacing the cerebrospinal fluid (CSF). Normal CSF is present on the left

side. The intralabyrinthine fluid and especially the fluid in the right cochlea have lost their high signal intensity (large white arrow) in comparison with the fluid in the normal left cochlea (white arrowhead). The signal difference is always seen better on the projection image

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Fig. 6.7. Neurovascular compression syndrome.

Paracoronal reconstruction of a set of gadolinium- enhanced MR angiography images in a patient with tinnitus and hemifacial spasm. The neural bundle can be followed in the IAC and cerebellopontine angle (arrowheads), and prominent blood vessels are resting on the superior border of the nerves near the root-entry zone (white arrows). The brain- stem (B) and temporal lobe (T) are indicated

Table 6.1. Magnetic resonance imaging protocol recommendations for temporal bone examinations

Pulse WI Plane No. of TR TE Flip Echo Section Matrix FOV recFOV BW No. Acq.

sequence sections (ms) (ms) angle train thickness of time

length (mm) acq. (min:s)

SE (T1±Gd) T1 tra/cor 10 490 20 90 – 2 160×256 230 62.5 65 4 5:17

GRE 3DFT- T2 tra 46 12.25 5.9 70 – 0.7 192×256 95 – 195 2 7:14

CISS

GRE-MRA – tra 64 39 7 25 – 1.13 192×512 240 75 81 2 8

3DFT-FISP

SE- T2 tra 19 1900 12/80 62 – 4 157×256 230 75 195/67 2 10

(brain stem)

Abbreviations: WI weighted image; TR repetition time (ms); TI inversion time (ms); TE echo time (ms); TD time delay (sec); no part number of partitions; Matrix (phase×frequency matrix); FOV field of view (mm); recFOV % rectangular field of view; BW bandwidth (Hz)

Table 6.2. Overview of imaging protocols for peripheral and central sensorineural hearing loss (SNHL), vertigo and tinnitus. Protocols should always begin with a T2-weighted brain study

Peripheral SNHL and vertigo General SNHL and vertigo Tinnitus

1. Axial unenhanced T1-weighted 1. T2-weighted brain stem sequence 1. Axial unenhanced T1-weighted

images images

2. Thin T2-weighted GRE sequence 2. Thin T2-weighted GRE sequence 2. Thin T2-weighted GRE sequence 3. Axial Gd-enhanced T1-weighted 3. Axiai Gd-enhanced T1-weighted 3. Axial Gd-enhanced T1-weighted

images images images

4. Coronal Gd-enhanced T1-weighted 4. Gd-enhanced T1-weighted 4. Gd-enhanced high resolution MRA

images brain study

5. Coronal T2-weighted study of the auditory pathways and cortex (SNHL) Bold = necessary: Italics = optional, call be omitted. Gd gadolinium; GRE gradient echo

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MR angiography (MRA) images should be used. This sequence is routinely added to the imaging protocol in patients with tinnitus (Fig. 6.7).

7. Selective, 4-mm-thick, SE T2-WI of the brainstem (axial) and auditory cortex (coronal) are used when more subtle pathology along the auditory/vestibular pathway is suspected (Fig. 6.2)

For an overview of the imaging protocols, see Tables 6.1 and 6.2.

6.1.4 Pathology

The most frequent pathology is ‘schwannoma’; these tumours can be found in the labyrinth, IAC (Fig. 6.4) and CPA. The second most frequent pathology in the membranous labyrinth is acute/chronic labyrinthitis (Fig. 6.3). Other frequently found lesions causing SNHL, vertigo, tinnitus or a combination of these clinical signs include labyrinthine malformations (Fig. 6.5), other types of CPA tumours such as meningiomas or epider- moids (Fig. 6.8), neurovascular conflicts (Fig. 6.7), brainstem infarctions (Fig. 6.2) or demyelination, etc.

MR imaging has become indispensable in patients who are candidates for cochlear implant surgery, as only the GRE T2-WI can inform the surgeon whether the cochlea is filled with fluid and whether a normal cochlear branch of the vestibulocochlear nerve is present.

Finally, in the middle ear, MR imaging is the method of choice for the detection of postoperative meningo(encephalo)coeles in patients with defects of the tegmen (Fig. 6.9).

6.2

Eye and Orbit 6.2.1

Introduction

CT scanning still plays an important role in the diagnosis of orbital pathology. The differences in attenuation values of the orbital contents (retrobulbar fat, extrinsic muscles, globe, bone, air and vessels) provide an excel- lent natural tissue contrast. However, MR imaging is the modality of choice when available. The major advantage of MRI over CT is that the entire visual pathway

can be examined in one go with higher sensitivity and specificity. In this manner, MR imaging not only detects orbital lesions, but is also able to demonstrate a wide range of intracranial pathology associated with visual impairment [parasellar lesions, multiple sclerosis (MS) plaques]. At present, CT still remains the imaging modality of choice in the following circumstances:

detection of calcifications, trauma patients, primary lesions arising from the bony orbit, or when MRI is not available. A drawback of MRI is that because of the longer examination time, it is more prone to globe and lid motion artefacts. Continuing efforts have been made by the MR vendors to overcome these problems by introducing faster imaging techniques. Fat-suppressed images allow better discrimination between enhancing structures located within the retrobulbar fat (Fig. 6.11).

6.2.2

Prior to performing MR imaging of the eye and orbit, patients must be screened in order to rule out the presence of metallic foreign bodies in or near the orbit, e.g., metallic slivers, fragments, or iron dust in industrial workers. These objects can move under the influence of the magnetic field, with blindness as a possible conse- quence. Therefore, thorough questioning of the patient is necessary. When in doubt, conventional X-rays should be obtained before positioning the patient in the magnet. Patients are asked to remove their mascara since it may contain ferromagnetic components, causing image degradation due to susceptibility artefacts. It is important to encourage the patient to fix his or her gaze on one point during the examination to avoid motion artefacts, which might arise during blinking.

The MR examination of the orbit can be performed using a circularly polarized head coil or a dedicated surface coil. Surface coils have the advantage of provid- ing a higher signal-to-noise ratio. Ultra-thin slices with a high spatial resolution (small FOV of 40–50 mm and high matrix of 512×512) can, thus, be obtained. This is useful to examine the globe for the presence of tumours (Fig. 6.10). A disadvantage of surface coils is that only the anterior portion of the orbit is depicted (the globe), leaving the remainder of the orbit and the optic pathway unexamined. A second disadvantage is that only one orbit can be visualized, unless binocular surface coils are used.

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Fig. 6.8A–C. Posterior fossa epidermoid tumour.

Transverse SE T2-WI (A), coronal Gd-enhanced SE T1-WI (B) and transverse GRE T2-WI (C) in a patient with an epidermoid tumour in the lower cerebellopontine angle (CPA). A larger lower CPA space is seen on the right side (black arrows), and also the signal intensity on the right side is slightly higher than on the left side (white arrows) (A). The lesion in the right CPA does not enhance (arrow- heads) and has a slightly higher signal intensity than the normal CSF in the left CPA (white arrows) (B). Only on the GRE T2-WI (C) can the lesion (white arrows) be distinguished from the surround- ing CSF. The solid nature of the tumour is proved, and a subarachnoid cyst can be excluded

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Fig. 6.9. CSF leak. Coronal Gd-enhanced SE T1-WI through the left middle ear in a patient with a CSF leak. A large tegmental defect can be seen (white arrows) with herniation of brain (long black arrows) into the middle ear cavity. It was impos- sible to recognize the presence of brain in the com- pletely obliterated middle ear on CT. There is adjacent inflammation and/or granulation tissue in the middle ear/antrum (large black arrow). The struc- ture above the tegmental defect is the temporal lobe (T)

Fig. 6.10A,B. Thin-section MR imaging of the globe using a sur- face coil of 5 cm. Transverse T2-WI (A) and transverse T1-WI after gadolinium injection (B) of the globe in a patient with retinoblas- toma. A bulky, heterogeneous, intraocular tumour mass (T) and

accompanying retinal detachment (E) are observed. Notice the presence of a small flow void in the tumour, reflecting small cal- cifications (arrow) (B) (Courtesy of Dr A. Lemke, Berlin)

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6.2.3

To reduce motion artefacts, the scanning time should be kept as short as possible. This can be achieved by reduc- ing the repetition time (TR) and/or the number of exci- tations (NEX). Thin slices (thickness of 3–5 mm) and a small FOV are combined to optimize spatial resolution.

For the MR protocol for imaging of the orbit and visual pathway, see Table 6.3.

1. High-resolution SE T1-W semiaxial or coronal imaging sequences are performed as the initial screening sequence. Both slice orientations allow comparison of both orbits. The semiaxial slices are oriented along the course of the optic nerve.

2. TSE T2-W and fat-suppressed sequences are added when a lesion is seen, and further characterization is required. Fat suppression is necessary to subdue the bright signal arising from the retrobulbar fat. This causes chemical-shift misregistration artefacts at fat- water interfaces (the margins of the globe) and, fur- thermore, the bright signal of the retrobulbar fat may overwhelm small structures of intermediate to low signal intensity (the use of fat suppression is mandatory for lesion demonstration in the optic nerve, e.g. optic neuritis). Fat suppression can be obtained by frequency-selective spectral presatura- tion or by short tau inversion recovery (STIR) techniques.

3. Gd-enhanced SE T1-WI with fat suppression may be required for further differentiation of tumours, optic nerve lesions and orbital masses. After intravenous injection of Gd, spectral fat saturation is the tech-

nique of choice (Fig. 6.11). STIR sequences should be avoided for post-contrast MR imaging, because the fat signal will be suppressed as well as the signal arising from enhancing structures. This phenome- non is known as negative enhancement.

4. GRE sequences are of limited use, but may detect changes in susceptibility in the presence of calcifications (retinoblastoma) or haemorrhage.

6.2.4 Pathology

Major indications for MRI of the eye and orbit include tumours (Tables 6.4 and 6.5), such as uveal melanoma

Table 6.4. Ocular tumours Uveal melanoma Metastasis

Choroidal haemangioma Retinoblastoma^a

Astrocytic hamartoma^a(tuberous sclerosis, neurofibromatosis)

aIntraocular calcifications

Table 6.5. Orbital tumours Optic nerve glioma

Optic nerve sheath meningioma Plexiform neurofibroma

Haemangioma (capillary, cavernous) Lymphangioma

Lymphoma – pseudotumour Rhabdomyosarcoma Metastases

Table. 6.3. Magnetic resonance protocol recommendations for imaging of the orbit and visual pathway

Pulse WI Plane No. of TR TE Flip TI Echo Section Matrix FOV recFOV BW No. Acq.

sequence sections (ms) (ms) angle (ms) train thickness of time

length (mm) acq. (min:s)

SE T1 tra/cor 15 450 15 90 – – 2 256×512 200 75 130 2 3:50

STIR T2 cor/tra 11 2700 19 90 150 – 3 192×256 200 75 130 1 6:39

TSE T2 tra/cor 15 3000 19–93 90 – 3 3 256×512 360 50 130 2 6:32

spectral T1 tra/cor 11 650 15 90 – – 3 192×256 230 75 130 2 4:10

fatsat – – – – – – – – – – – – FS63

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Fig. 6.11A–D. Idiopathic inflammatory pseudotumour. Transverse SE unenhanced T1-WI (A), turbo SE (TSE) T2-WI (B), SE Gd- enhanced T1-WI without (C) and with (D) spectral fat suppres- sion in a patient with idiopathic inflammatory pseudotumour of the right orbit. An intraconal mass lesion with signal intensity iso- intense to muscle is noticed in the apex of the right orbit (A). The lesion extends into the cavernous sinus. On the T2-W sequence, the lesion displays a low signal intensity, reflecting a high cellular content (B). After contrast injection, enhancement of the lesion is difficult to detect because of the high signal intensity of the retro- bulbar fat (C). A sequence with spectral fat suppression shows enhancement of the lesion located in the orbital apex (D). Note also the normal enhancement of the extraocular muscles and of the choroidal layer in the globe

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(Fig. 6.12), retinoblastoma (Fig. 6.10), optic-nerve glioma, optic nerve sheath meningioma (Fig. 6.13), haemangioma (Fig. 6.14) and metastases (Fig. 6.15). Also, inflammatory lesions of the orbit, e.g. idiopathic inflammatory pseudotumour (Fig. 6.11) and inflammatory lesions of the optic nerve (Fig. 6.16), may be demonstrated. Lesions that arise outside the orbit and inter- fere with the function of the optic pathways can be seen, e.g. pituitary macroadenoma (Fig. 6.17).

6.3

Paranasal Sinuses 6.3.1

Introduction

CT and MRI are complementary techniques for imaging the paranasal sinuses. The bony structures surrounding the air-filled sinus cavities are better seen on CT. Therefore, CT is the preferred imaging modality in trauma patients. Moreover, CT is superior in demon- strating the ostiomeatal complex, which occupies a key position in inflammatory/infectious disease, especially when functional endoscopic sinus surgery (FESS) is planned. The use of MR imaging is advocated in patients with complicated inflammatory sinus disease and in patients with suspected tumoral pathology in this region.

6.3.2

The patient is placed in a supine position in the circularly polarized head coil with the head firmly fixed.

6.3.3

1. The MR examination of the paranasal sinuses starts with coronal unenhanced SE T1-WI and TSE T2-WI . The purpose of these sequences is to discriminate between different soft-tissue structures and retention of serous and mucinous fluid.

2. Contrast-enhanced, high-resolution, axial and coronal SE T1-WI are obtained to further differentiate soft-tissue structures, thereby allowing discrimination between tumoral components from normally enhancing mucosa or polyps (Figs. 6.18 and 6.19).

Also, intracranial and/or intraorbital extension of pathology can be better demonstrated in this manner (Fig. 6.20).

For the MR imaging protocol for sinonasal examinations, see Table 6.6.

Fig. 6.12A,B. Uveal melanoma. Fat-suppressed transverse SE T1- weighted images (T1-WI) before (A) and after (B) Gd injection in a patient with an uveal melanoma of the left globe. A fusiform, spontaneously hyperintense, nodular lesion (A) is observed in the lateral part of the left eye globe. The high signal intensity on the precontrast image indicates the presence of a paramagnetic sub- stance such as melanin. Intense enhancement of the lesion is observed after Gd injection (B)

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Fig. 6.13A–D. Optic nerve sheath meningioma in a patient with neurofibromatosis type 2 (NF 2). Sagittal SE T1-WI (A) and Gd- enhanced SE sagittal (B), transverse (C) and coronal (D) T1-WI in a 25-year-old man with NF 2. On the precontrast image, there is a fusiform mass lesion centred around the left optic nerve (A).

There is a second lesion at the vertex, which appears to arise from the diploë, with meningeal thickening and extracranial soft tissue.

After Gd injection, the tumour around the optic nerve enhances intensely (B,C). On the axial image (C), the optic nerve is not thickened, and the tumour is seen to originate in the perioptic sheath, indicating the diagnosis of optic nerve sheath meningioma. The intra-osseous meningioma at the vertex also enhances intensely (B,D). Note the thickening and enhancement of the cal- varial dura (B,D). In the setting of NF 2, other intracranial lesions are seen in this patient: a nodular enhancing lesion near the fora- men of Luschka, presumably an ependymoma (B), a small plate- like enhancing meningioma along the right tentorial attachment (C), an enhancing nodule in the prepontine cistern (C) and bilat- eral acoustic schwannomas (D). Bilateral acoustic schwannomas are the hallmark of the diagnosis of NF 2. Moreover, patients with NF 2 are known to have multiple central nervous system tumours (the acronym MISME indicates: multiple inherited schwannomas, meningiomas and ependymomas)

Fig. 6.14A–C. Intraconal cavernous haemangioma of the right orbit. Transverse turbo TSE T2-WI (A), transverse SE T1-WI with spectral fat saturation before (B) and after (C) Gd injection in a 27-year-old man presenting with proptosis of the right eye. A heterogeneous, lobulated, retrobulbar mass of the right orbit is observed. On T2-WI, the lesion is markedly hyperintense (A). The lesion contains areas of high signal intensity on T1-WI (B) that may represent areas of thrombosed vascular spaces. Cavernous haemangiomas always enhance after Gd injection (C)

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Fig. 6.15A–D. Bilateral rectus muscle metastases. Transverse SE proton density-weighted images (T1-WI) (A), transverse TSE T2- WI (B) and transverse SE T1-WI (C) and transverse fat-sup- pressed T1-WI (D) after Gd injection in a 77-year-old woman with a previous medical history of breast carcinoma. Enlargement of the right lateral rectus muscle and of the left medial rectus muscle

is observed. Signal intensities are nonspecific, and without her clinical history, the differential diagnosis should include idiopathic inflammatory pseudotumour, lymphoma and thyroid ophthal- mopathy. In children, rhabdomyosarcoma is the most common primary malignant orbital tumour

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Fig. 6.16A,B. Optic neuritis. Coronal short tau inversion recovery (STIR) image through the orbits (A) and transverse proton den- sity-WI through the cerebral hemispheres (B). On the normal right side, there is a ‘target appearance’, which is caused by the CSF-filled meningeal sheath surrounding the optic nerve (A). On the abnormal left side, the ‘target appearance’ has disappeared due to swelling and inflammation of the left optic nerve in a patient with relapsing remitting multiple sclerosis (MS) (A). The proton density-WI through the brain reveals multiple punctate white matter abnormalities in both hemispheres (B). The multifocality, morphology, distribution and location of the lesions suggest the diagnosis of MS

Fig. 6.17A,B. Pituitary macroadenoma. Sagittal SE T1-WI (A) and coronal Gd-enhanced SE T1-WI (B) through the pituitary gland and parasellar region.

The suprasellar component of the pituitary macroadenoma displaces and compresses the optic chasm. The lesion arises from the left lobe of the pituitary gland and invades the left cavernous sinus. There is also extension into the sphenoid sinus

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Fig. 6.18A–D. Inverted papilloma. Coronal SE T1-WI (A), trans- verse TSE T2-WI (B) and Gd-enhanced SE T1-WI with spectral fat saturation in the transverse (D) and coronal planes (C) in a 60- year-old man with complaints of nasal obstruction and epistaxis.

The lesion appears to arise from the lateral nasal wall near the middle turbinate and extends into the left maxillary sinus (A).

There is remodelling of the medial wall of the maxillary sinus,

without frank bone destruction. Complete opacification of the maxillary sinus is noticed. No differentiation can be made between tumoral tissue, normal mucosa and retention of mucus on the pre-contrast T1-WI (A). After Gd injection (C,D), there is enhancement of the normal mucosa with heterogeneous enhancement of the tumour. No enhancement is noticed in the retained secretions. Biopsy of the lesion demonstrated inverted papilloma

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Fig. 6.19A,B. Sinonasal adenocarcinoma. Transverse TSE T2-WI (A) and Gd-enhanced SE T1-WI (B) in an 85-year-old man, with biopsy-proven nasal adenocarcinoma. A low signal-intensity lesion is noticed in the nasal fossae with extension of the lesion through the choanae into the nasopharynx. The posterior part of the tumour is even more hypointense, presumably reflecting the high cellularity of the lesion (A). The tumour causes obstruction

of the ostiomeatal complex; the retained secretions in the maxil- lary sinuses are hyperintense on T2-WI (A). After Gd injection, the tumour enhances (B). The area of enhancement extends posteri- orly in the parapharyngeal spaces and into the right longus colli muscles, indicating tumoral invasion and/or reactive changes. In the maxillary sinuses, the mucosa enhances, whereas the retained fluid does not

Fig. 6.20. Recurrent ethmoid adenocarcinoma.

Coronal Gd-enhanced, high-resolution SE T1-WI through the anterior skull base in a patient with a recurrent ethmoid adenocarcinoma. Tumour recur- rence (T) can be seen in the right ethmoid region.

Enhancement of the meninges can be depicted above the right cribriform plate (arrowheads), and enhancement of the olfactory bulb (large white arrow), representing tumour invasion, can also be recognized. Compare with the normal low signal intensity of the left olfactory bulb (long white arrow)

Table 6.6. Magnetic resonance imaging protocol recommendations for sinonasal examinations

Pulse WI Plane No. of TR TE Flip Echo Section Matrix FOV recFOV BW No. Acq.

sequence sections (ms) (ms) angle train thickness of time

length (mm) acq. (min:s)

SE T1 cor/tra 19 570 15 90 – 5 192×512 230 75 130 2 3:39

TSE T2 cor/tra 26 8000 90 90 12 3 240×256 130 – 130 2 5:20

Abbreviations: WI weighted image; TR repetition time (ms); TI inversion time (ms); TE echo time (ms);TD time delay (sec); no part number of partitions; Matrix (phase×frequency matrix); FOV field of view (mm); recFOV % rectangular field of view; BW bandwidth (Hz)

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6.3.4 Pathology

Complications of inflammatory sinus diseases, such as mucocoele (Fig. 6.21), brain abscess or subdural empye- ma, cavernous sinus thrombosis, meningitis, etc., are much better demonstrated on MRI than CT. MRI is indicated to demonstrate the exact extent of tumoral lesions and discriminate them from normal mucosa

and secondary retention of fluid, whereas on CT only opacification of the sinuses will be seen. Tumoral lesions (Table 6.7) include both benign (inverted papilloma, juvenile angiofibroma, fibro-osseous lesions, etc.) (Fig. 6.18) and malignant lesions [squamous cell carcinoma (SCCA), adenocarcinoma, adenoid cystic carcinoma, lymphoma, esthesioneuroblastoma, etc.] (Figs.

6.19 and 6.20).

Fig. 6.21A–C. Mucocoele. Transverse SE T1-WI (A) and transverse (B) and coronal WI (C) TSE T2-WI at the level of the sphenoid sinus in a patient who complained of progressive diplopia.

Spectral fat saturation was applied in all sequences. An expansile lesion with high signal intensity is noticed at the sphenoid sinus.

There is clear expansion of the sinus cavity with intraorbital extension of the mucocoele and displacement of the medial rectus muscle. The signal intensity of a mucocoele depends on the vis- cosity of the secretions

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6.4 Skull Base 6.4.1 Introduction

The bony structures of the skull base are easier to recognize on CT. However, lesions of the skull base can also involve the extracranial and intracranial soft tissues, the nerves and vessels in the skull base foramina, and the bone marrow. Only MRI provides adequate contrast and spatial resolution to distinguish all these structures and has, therefore, become the method of choice to study skull-base lesions and cranial nerve involvement.

6.4.2

A standard, circularly polarized head coil provides the best images of the skull base. Patients are examined in the supine position, and their head is placed as high as possible in the head coil. The closer the skull base is to the centre of the head coil, the better the image quality.

Images are made parallel and/or perpendicular to the part of the skull base to be examined.

6.4.3

The MR technique will depend on the structures surrounding the region of interest.

1. Gd-enhanced, high-resolution SE T1-WI are used when cortical bone, soft tissues and nerves surrounded by bone or soft tissues must be visualized (Fig. 6.20).

2. In the central skull base and especially in the posterior skull base, nerves and vessels approach the skull base surrounded by cerebrospinal fluid (CSF). In these regions, normal nerves and tumour extension along nerves are best seen on transverse GRE T2-WI.

On these images the tumour/nerves are seen as intermediate to low signal-intensity structures, out- lined by high signal-intensity CSF (Fig. 6.22).

3. Within the skull-base foramina, the nerves, vessels and surrounding bone are best distinguished from one another when high-resolution (3DFT-FISP) time-of-flight MRA images are used. These images should be contrast enhanced so that the venous lakes become hyperintense and provide a different signal intensity from the nerves and surrounding bone (Fig. 6.23).

4. Lesion characterization and screening of the skull base can be performed using high-resolution transverse TSE T2-WI (Fig. 6.24). This sequence can also be used as the first screening sequence in severe pathology.

The parameters of these four routine skull-base sequences are shown in Table 6.8.

Contrast-enhanced, high-resolution T1-WI with fat suppression can be used to detect bone-marrow invasion, and they sometimes are better at distinguishing tumour from normal fat. Unenhanced SE T1-WI remain the most sensitive images to detect bone-marrow invasion.

6.4.4 Pathology

MRI is used in the skull base mainly to evaluate tumour extension (especially along nerves and vessels), detect bone invasion and achieve better tumour characterization. Tumours can originate intracranially in the marrow/cortical bone of the skull base or in the extracranial soft tissues. All possible extension routes through neuroforamina should be checked. Inflammatory lesions, congenital malformations, traumatic lesions and all types of cranial nerve pathology may also involve the skull base and be studied by MRI. However, congenital malformations and traumatic lesions are best studied with CT, with some exceptions. The anteri- or skull base is best studied in the coronal and sagittal planes. Unenhanced and Gd-enhanced high-resolution SE T1-WI are best suited to study the olfactory bulbs Table 6.7. Paranasal sinus masses

Mucocoele

Mucus retention cyst Polyp

Antrochoanal polyp Inverted papilloma Sinusitis

Carcinoma

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Fig. 6.22A,B. Skull-base metastasis near the right jugular foramen. Transverse Gd-enhanced SE T1- WI (A) and GRE T2-WI (B) at the level of the medulla oblongata in a patient with hoarseness and difficulty swallowing. A nodular enhancing struc- ture (small white arrows) is observed near the entrance of the right jugular foramen, and it is unclear whether we are dealing with flow in a venous structure or with a mass (A). There is an enhancing metastasis that can be seen in the ante- rior part of the brain stem (large white arrow).

Notice the normal appearance of the left jugular foramen (long white arrow). The glossopharyngeal nerve is seen bilaterally (arrowheads). On the thin GRE images (B), a low signal-intensity metastasis on the glossopharyngeal nerve replaces the CSF near the intracranial entrance of the jugular fora- men (long arrows). Compare with the normal CSF, which can be followed until the jugular foramen is reached on the left side (large black arrow). Again, the glossopharyngeal nerves are seen even better (arrowheads)

Table 6.8. Magnetic resonance imaging protocol recommendations for examinations of the skull base

Pulse WI Plane No. of TR TE Flip Echo Section Matrix FOV recFOV BW No. Acq.

sequence sections (ms) (ms) angle train thickness of time

SE T1 tra/cor/ 20 450 12 90 – 4 384×512 220 75 130 3 8:41

(T1+Gd) sag

GRE T2 tra 46 12.25 5.9 70 – 0.7 192×256 95 – 195 1 7:14

3DFT-CISS

GRE-MRA – tra 64 39 7 25 – 1.15 192×512 240 75 81 1 8

3DFT-FISP

TSE-T2 T2 tra 20 4000 99 180 11 4 242×512 300 50 130 2 3

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Fig. 6.23A,B. Glomus vagale. Transverse Gd- enhanced 1-mm-thick MRA image through the right jugular foramen (A) and parasagittal MRA reconstruction (B) in a patient with a glomus vagale tumour. A hypointense mass (black arrow- heads) with central hyperintense signal intensities (flow) can be seen behind the internal carotid artery (large white arrow). The adjacent Gd- enhanced sigmoid sinus (small white arrows) and venous structures in the hypoglossal canal (long white arrows) make the hypointense mass visible (A). The inferior petrosal sinus is identified (white arrowheads). In the reconstructed image (B), the glomus vagale tumour has an intermediate inho- mogeneous signal intensity (small white arrows), and high signal-intensity vessels are present inside the tumour (long black arrows), revealing the nature of the mass. The exact extension of the intermediate signal-intensity tumour (black arrow- heads) inside the jugular foramen can be recog- nized, due to the high signal intensity of the sur- rounding Gd-enhanced venous blood (large black arrow) (B). C, cerebellum; carotid artery (large white arrows)

and tracts (trauma patients, congenital anosmia, etc.) and tumours originating in the sinuses or intracranially (meningiomas, esthesioneuroblastomas, etc.).

Coronal, thin GRE T2-WI are only required when a CSF leak or meningo(encephalo)coele is suspected. The central skull base and especially the parasellar region and neuroforamina are best studied in the coronal and transverse planes with high-resolution SE T1-WI. Most of the tumoral lesions and cranial nerve lesions may be studied this way and, when necessary, be further char- acterized using TSE T2-WI. Transverse MRA images are only used when aneurysms or vascular pathology is suspected. Transverse GRE T2-WI are used when posterior extension into the prepontine cistern or CPA is

present. In the posterior skull base, axial and coronal images perform best. The sagittal plane is only used to study midline lesions of the clivus and craniocervical junction. High-resolution T1-WI are used to study tumours and look for abnormal enhancements in tumoral and inflammatory lesions. Thin, transverse GRE T2-WI are often used to study the relationship of the lesions to the cranial nerves VI to XII in the cisterns surrounding the lower brainstem. Finally, transverse, high-resolution, Gd-enhanced MRA images are needed when a lesion involves or grows through the jugular foramen.

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6.5

Nasopharynx and Surrounding Deep Spaces and Parotid Glands

6.5.1 Introduction

The nasopharynx is an anatomic area in the head and neck region, which is difficult to visualize clinically.

Moreover, the surrounding deep spaces cannot be examined clinically, and lesions in these spaces only become visible when they become sufficiently large or start to involve surrounding structures, such as nerves, blood vessels, etc. Therefore, high-quality imaging is

needed in these anatomical regions. Only MRI is able to consistently provide images with sufficient tissue-contrast resolution and spatial resolution in these regions and, therefore, is the imaging modality of choice.

6.5.2

A selective examination of the nasopharynx and surrounding spaces is best performed with a standard head coil. Patients are examined in the supine position with the head positioned as high as possible in the head coil. To obtain high-quality images, the patients should Fig. 6.24A,B. Clival chordoma. Sagittal Gd-

enhanced T1-WI (A) and axial T2-WI (B) through the clivus in a patient with a chordoma. A bilobular enhancing mass can be seen behind the sphenoid sinus (S) and in the clivus (white arrows). The sag- ittal plane is best suited to image these midline lesions and also demonstrates the displacement of the brainstem. On the T2-WI (B) through the level of the IAC (arrowheads), the mixed signal inten- sities inside the tumour (white arrows), the multi- ple convex peripheral protrusions and the midline location further help to establish the diagnosis of a chordoma. The basilar artery (black arrow) is com- pressed between the chordoma and the brainstem

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be instructed to avoid motion, swallowing and talking, because it degrades the images. Breathing through the nose with the mouth closed also reduces motion artefacts.

A dedicated neck coil is used when the complete oral cavity or complete oropharynx must also be included, or when a complete staging of the neck lymph nodes is required (see Sect. 6.6).

The parotid glands can be examined with surface coils. With these coils, higher spatial resolution can be achieved, but there is a drop in signal intensity from the superficial to the deep part of the gland, and this may result in insufficient visualization of the deep lobe.

Another drawback is that only one gland is examined with a surface coil. Therefore, we prefer a head coil for imaging the parotid glands. In order to increase the spatial resolution, a 512×512 matrix is used. Another advantage is that the patient is better fixed in a head coil, and this will result in fewer motion artefacts than with a surface coil. Again, the patient must be positioned as high as possible in the head coil so that the inferior part of the parotid gland can be included in the imaging FOV (Fig. 6.25). The preferred slice orientation for the above-mentioned studies is the axial plane, parallel to the hard palate. A nasopharynx study should start at the superior border of the pituitary fossa in order to exclude intracranial extension. The inferior reference is the inferior border of the mandible; however, the signal is often already insufficient at this level when a head coil is used. A parotid-gland study starts at the superior border of the external auditory canal and ends at the inferior border of the mandible. When additional coronal slices are used, they are made in a plane perpendicular to the hard palate.

6.5.3

The nasopharynx, surrounding deep spaces and parotid glands are best examined in the transverse plane; the MR imaging protocol for examinations of these regions is shown in Table 6.9.

1. Transverse high-resolution TSE T2-WI can be used as the first sequence. These images have a high contrast and spatial resolution, making them very sensitive for the detection of parotid lesions. Moreover, these images are needed when further tissue characterization is necessary (Fig. 6.25).

2. The MR examination continues with transverse unenhanced and Gd-enhanced high-resolution SE T1-WI. The unenhanced images are the most sensitive images in the detection of bone-marrow involvement and, therefore, can detect early skull-base or mandible invasion. Moreover, they prevent confu- sion of areas with high signal intensity on T1 images (blood, fat, proteinaceous fluid, etc.) with areas of enhancement. Gd-enhanced T1-WI have a better signal-to-noise ratio than the unenhanced images, and this results in better tumour delineation. The solid and cystic parts of a tumour are also better distinguished on the Gd-enhanced images (Figs. 6.25 and 6.26).

3. Additional coronal Gd-enhanced T1-WI of a nasopharynx lesion or a lesion of the surrounding spaces or the parotid gland often provide important information about the exact location and extension of the tumour. These are mandatory when the skull base is invaded.

4. Finally, the transverse and coronal Gd-enhanced images can be replaced by similar images with spec-

Table 6.9. Magnetic resonance imaging protocol recommendations for nasopharyns, surrounding deep spaces and parotid gland exami- nations

Pulse WI Plane No. of TR TE Flip Echo Section Matrix FOV recFOV BW No. Acq.

sequence sections (ms) (ms) angle train thickness of time

TSE-T2 T2 tra 20 4000 99 180 11 4 242×512 300 50 130 2 3

SE T1 tra/cor 20 450 12 90 – 4 384×512 220 75 130 3 8:41

(T1±Gd)

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tral fat suppression. On these images, tumour enhancement can be better distinguished from the surrounding fat. The drawback of fat suppression is that fewer slices are available when the same acquisition time is used. Therefore, the slice thickness

should be increased if the complete region must be imaged, or the total acquisition time must be increased. Also, the signal-to-noise ratio is inferior on images with fat suppression.

Fig. 6.25A–C. Pleomorphic adenoma. Transverse TSE T2-WI (A) and Gd-enhanced SE T1-WI in the transverse (B) and coronal planes (C) in a patient with a pleomorphic adenoma of the left parotid gland. Both the pleomorphic adenoma (black arrows) in the left parotid gland and the normal right parotid gland (small white arrows) can be studied in detail on high-resolution T2-WI when the head coil is used (A). The T2-weighting helps to distin- guish the high-contrast lesion from the intermediate signal of the gland and also highlights the cystic component of the tumour (large white arrow). After Gd injection (B), both parotid glands can be studied in detail, but the solid part (black arrows) and cys-

tic part (large white arrows) of the tumour are more difficult to distinguish from each other and from the surrounding normal parotid gland. The right parotid gland is normal (small white arrows). The coronal plane (C) often provides additional informa- tion about the position of the tumour (large black arrows) with regard to the remaining normal gland (white arrows), the adjacent blood vessels (arrowheads) and the skull base. The signal-to-noise ratio is still sufficient to allow evaluation of the inferior part of the parotid gland when the head coil is used. Notice the mandibular nerve in the oval foramen (small black arrow) and masticator space (long black arrows)