9 Parapharyngeal Space Neoplasms Robert Hermans

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9 Parapharyngeal Space Neoplasms

Robert Hermans and Davide Farina

R. Hermans, MD, PhD

Professor, Department of Radiology, University Hospitals Leuven, Herestraat 49, 3000 Leuven, Belgium

D. Farina, MD

Department of Radiology, University of Brescia, Piazzale Spedali Civili 1, 25123 Brescia, BS, Italy

lignant lesion. Clinical assessment of tumors in this region is often difﬁ cult, commonly causing a delay between the onset of clinical manifestations and the diagnosis. Bulging of the lateral nasopharyngeal wall may be appreciated, associated with displacement of the soft palate and palatine tonsil. When a PPS lesion grows laterally, facial swelling may result at the level of the parotid or submandibular region. Rarely, the mandible will be displaced by a slowly growing tumor (Farina et al. 1999).

Physical examination may not allow differentiation between a PPS neoplasm and a parotid gland lesion originating in the deep lobe. Before the advent of cross- sectional imaging techniques, such as CT and MR, treatment was performed via a transparotid approach.

Nowadays, when a CT or MR study demonstrates the lesion to be in the PPS, most patients are operated via a transcervical approach, with or without resection of the deep lobe of the parotid gland. In large tumors, mandibulotomy may be required to remove the tumor.

In selected small tumors, a transoral approach may be sufﬁ cient. The use of imaging studies has resulted in a signiﬁ cant decrease of transient or permanent dam- age to the facial nerve (Stell et al. 1985; Olsen 1994;

Miller et al. 1996; Luna-Ortiz et al. 2005).

Lesions arising from the adjacent spaces displace the PPS in a particular way, allowing the radiologist to identify precisely the space of origin. Combining the imaging characteristics of the lesion with a limited space-speciﬁ c differential diagnosis often allows a precise diagnosis. Knowledge of the anatomy is, therefore, the key to unlock the PPS and its related spaces.

9.2 Anatomy

9.2.1

Fascial Layers and Compartments

Medially, the PPS is in close contact with the pharyngeal mucosal space, bordered by the middle layer of

CONTENTS

9.1 Introduction 163 9.2 Anatomy 163

9.2.1 Fascial Layers and Compartments 163 9.2.2 Radiological Anatomy 165

9.3 Imaging of Parapharyngeal Space Lesions 166 9.3.1 Primary Lesions of the Parapharyngeal Space 166 9.3.2.1 Prestyloid Lesions 166

9.3.2.2 Retrostyloid Lesions 169

9.3.2 Secondary Lesions of the Parapharyngeal Space 170 References 174

9.1 Introduction

The parapharyngeal space (PPS) is a deep space of the neck shaped as a tilted up pyramid with its base attach- ing to the skull base and the apex reaching the level of the hyoid bone, and almost exclusively containing fat. Primary neoplasms arising in this space are quite rare, accounting for only 0.5% of all head and neck tumors (Olsen 1994; Miller et al. 1996; Pang et al.

2002), whereas the PPS is more commonly displaced or inﬁ ltrated by lesions arising in the adjacent spaces, including the pharyngeal mucosal, masticator, parotid, and retropharyngeal spaces. Approximately 70%–80%

of the tumors originating from the PPS itself are benign (Luna-Ortiz et al. 2005).

Small tumors of the PPS, with a size of less than 2.5 cm, are often incidental ﬁ ndings. Larger tumors produce aspeciﬁ c signs and symptoms, including sore throat, ear fullness, dysphagia and, less frequently, jaw pain combined with cranial nerves palsy.

These last two symptoms may be caused by a ma-

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164 R. Hermans and D. Farina

the deep cervical fascia (also known as buccopharyngeal fascia), which curves around the posterior and lateral side of the pharyngeal mucosal space, surrounding the constrictor muscles (Figs. 9.1 and 9.2).

Superiorly, the pharyngeal constrictor muscle does not reach the skull base; at that level, the lumen of the nasopharynx is held open by the thick pharyngobasilar fascia. This fascia lies within the middle layer of the deep cervical fascia. The pharyngobasilar fascia is interrupted at the level of the sinus of Morgagni, an opening through which the cartilaginous part of the Eustachian tube and the levator veli palatini muscle enter the nasopharynx. This area should be carefully inspected on imaging studies of the nasopharynx, as it is a common route of spread for nasopharyngeal carcinomas from the mucosal space to the skull base (see Chap. 8). Just posterior to the Eustachian tube is the fossa of Rosenmüller, a mucosal recess where most of the nasopharyngeal carcinomas arise.

The superﬁ cial layer of the deep cervical fascia is lateral to the PPS, separating this space from the masticator space. This fascia curves around the medial surface of the pterygoid muscles and extends from the mandible to the skull base, where it attaches just medial to the foramen ovale. As a consequence, the mandibular nerve (V3), as it courses through this foramen, directly enters the masticator space.

In its posterolateral portion, the PPS is in contact with the deep lobe of the parotid gland. The existence of a fascial layer at this level is controversial.

The anterior border of the PPS is the pterygomandibular raphe. Inferiorly, the PPS gradually becomes narrower and ends at the level of the hyoid bone and superior margin of the submandibular salivary gland.

The posterior border of the PPS is the most complex and controversial; different descriptions are found in the literature. Some authors consider the PPS completely separate from the more posterior carotid space: the anterior surface of the carotid sheath (made up of the three layers of deep cervical fascia) draws the borderline between the two spaces. From a radiological point of view such a separation allows a precise and reliable space-speciﬁ c differential diagnosis (Som and Curtin 1995). Others, in contrast, consider the carotid sheath and, consequently, the carotid space to be part of the PPS (Mukherji and Castillo 1998).

Three more fascial structures are described, act- ing as anatomical landmarks subdividing the PPS.

The tensor-vascular-styloid fascia (TVS) is a layer that extends from the inferior border of the tensor veli palatini muscle, posterolaterally and inferiorly to the styloid process and muscles (Fig. 9.2). Anteriorly, it reaches the pterygomandibular raphe and there-

Fig. 9.1a,b. Axial T1-weighted spin-echo image (a) at the level of the soft palate. The boundaries of the parapharyngeal space (PPS) (including prestyloid and retrostyloid compartment) are indicated by arrows and arrowheads on the right. On the left, the adjacent spaces are labeled: 1, pharyngeal mucosal space; 2, masticator space; 3, parotid space; 4, retropharyngeal/prevertebral space. b Coronal T1-weighted spin-echo images through prestyloid compartment of the PPS. Inferiorly, this space is closed by the submandibular gland (5), while superiorly, it reaches the skull base (6). The foramen ovale (arrow), through which exits the mandibular nerve, communicates with the masticator space. The styloglossal muscles run through the PPS (arrowheads)

a b

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fore it closes the gap between the skull base, the tensor veli palatini muscle and the styloid process (Som and Curtin 1995). The stylopharyngeal fascia splits on a coronal plane connecting the styloid process to the pharyngobasilar fascia, at the level of the fossa of Rosenmüller. In this same site a third layer, Charpy’s fascia, also known as the ‘cloison sagittale’, arises, oriented on a sagittal plane and posteriorly reaching the prevertebral fascia where it attaches to the lateral cervical processes.

The TVS fascia allows further subdivision of the parapharyngeal space into two compartments: the prestyloid compartment, lying between the pterygoid muscles and the TVS fascia, and the retrostyloid compartment, just medial to the TVS fascia itself and including the carotid space (Maroldi et al. 1994;

Nasser and Attia 1990).

The PPS mainly contains fat tissue and loose con- nective tissue. In the prestyloid compartment ectopic minor salivary glands and vascular structures (pharyngeal ascending and internal maxillary artery, pharyngeal venous plexus) are found. The retrostyloid PPS contains the internal carotid artery (ICA), the internal jugular vein (IJV), the cranial nerves IX–XII, and the sympathetic plexus. Lymph nodes of the deep cervical chain, known as the jugulodigastric lymph nodes, are present in the retrostyloid compartment, below the level of the posterior belly of the digastric muscle (Grégoire et al. 2003).

9.2.2

Radiological Anatomy

When dealing with pathology at the level of the PPS, MRI has an advantage over CT because of its higher contrast resolution. CT better demonstrates subtle bone erosion. However, MR yields unique informa- tion about the medullary bone, which normally has a hyperintense signal on the unenhanced T1-weighted images (due to its fatty content). This signal will be- come hypointense on the same sequence when the medullary bone is replaced by neoplastic tissue. This signal decrease is a very sensitive sign for neoplastic infi ltration, but it is rather aspecifi c, because edema and infl ammatory bone reactions also cause a signal decrease in the medullary bone on T1-weighted images.

In the axial plane the prestyloid compartment of the PPS is recognized as a triangular fat-ﬁ lled space (Fig. 9.1) with maximum width at the level of the soft palate. While CT is unable to display the pharyngobasilar fascia, this fascia is visible on MRI as a hypointense line (Fig. 9.3).

The sinus of Morgagni is not visible with MR, but the Eustachian tube, particularly at the torus tubar- ius, where it opens in the nasopharyngeal lumen, can be used as an anatomical landmark.

The TVS, stylopharyngeal and Charpy’s fascia can not be routinely identiﬁ ed on MR. Their course can be

Fig. 9.2. Topographical anatomy of the PPS in the axial plane, including the different fascial layers at this level Pterygoid process Masticator space

Superﬁ cial layer of deep cervical fascia Mandible

Tensor-vascular-styloid fascia

Stylopharyngeal fascia

Parotid gland (deep lobe) Styloid process Internal jugular vein Digastric muscle (posterior belly) Mastoid process Deep layer of deep

cervical fascia Vagal nerve

Internal carotid artery Sympathetic chain

Charpy’s fascia Retropharyngeal lymph node Prevertebral fascia Alar fascia Buccopharyngeal fascia Pharyngobasilar

fascia Eustachian tube Levator veli palatini muscle Tensor veli palatini muscle

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• To identify hypervascular neoplasms in order to avoid biopsy and its possible complications.

9.3.1

Primary Lesions of the Parapharyngeal Space

Primary lesions of the PPS are rare and most are benign. These lesions can be classiﬁ ed based on histology (three main groups: salivary, neurogenic, paragangliomas), or according to the compartment of origin (prestyloid or retrostyloid).

9.3.2.1

Prestyloid Lesions

The overwhelming majority of neoplasms in the prestyloid compartment are salivary gland tumors.

Most other lesions in this compartment are related to anomalies of the branchial apparatus.

Pleomorphic adenoma is the most frequent salivary tumor. These tumors may arise from ectopic minor salivary glands, localised in the prestyloid compartment along the embryological growth path of the parotid gland, but much more often they originate from the deep lobe of the parotid gland.

Making the differentiation between a primary prestyloid PPS lesion and a neoplasm of the deep lobe of the parotid gland is important, because, in the latter case, the deep lobe of the parotid gland also needs to be resected.

Fig. 9.3a,b. Axial gadolinium-enhanced T1-weighted spin-echo images, showing the relationship between the superior constric- tor muscle, the pharyngobasilar fascia and a nasopharyngeal cancer. a Axial section at level of soft palate. The superior con- strictor muscle (arrowheads) is surrounding the nasopharynx; the tumor (asterisk) is conﬁ ned to the nasopharyngeal lumen.

b. At a higher level, the nasopharyngeal lumen is bordered by the pharyngobasilar fascia (arrowheads). Bilaterally, the tensor veli palatini muscle (black arrow) is visible on the outer side of this fascial layer. On the right, the tumor extends into the PPS through the pharyngobasilar fascia (white arrow); this site likely corresponds to the sinus of Morgagni

a b

mentally outlined on axial scans by using the tensor veli palatini muscle and styloid process as anatomical landmarks. This last structure, easily detected with CT, is seen on MR with a characteristic ‘target’ appearance: hypointense external cortical rim with hyperintense bone marrow in its center.

The lateral fascial border of the PPS is not identi- ﬁ ed, but its cranial attachment lies just medial to foramen ovale (Fig. 9.1). MR is able to depict the course of the mandibular nerve – from Meckel’s cave, through the foramen ovale – and also the proximal segment of the main terminal branch, the inferior alveolar nerve, as it runs to the entrance of the mandibular canal.

The ICA and IJV, just medial to the styloid process, appear hyperdense on enhanced CT, while they generally show a ﬂ ow void on T1- and T2-weighted MR sequences. High or inhomogeneous signal is often seen in the jugular vein due to turbulent or slow ﬂ ow and should not be mistaken for a strongly enhancing mass (e.g. glomus jugulare tumor).

9.3 Imaging of Parapharyngeal Space Lesions

The role of imaging in lesions at the level of the PPS can be summarized in two key points:

• To precisely identify the space of origin; this allows to reduce the differential diagnostic list to a limited number of possibilities.

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The most reliable sign of a primary PPS tumor is the presence of a fat layer separating the tumor from the deep lobe of the gland. A deep parotid lobe tumor appears as a more or less dumbbell-shaped mass, connected to the parotid gland, potentially widening the stylomandibular tunnel, and displacing anteromedially the PPS fat (Fig. 9.4).

Pleomorphic adenomas usually show the follow- ing MR appearance: hyperintense signal intensity on T2-weighted sequences, related to their myxoid component, and often pronounced enhancement with fo- cal areas of hypointensity on T1-weighted sequences.

However, various signal intensities due to haemor- rhage, calciﬁ cations and necrosis may be seen within such a tumor (Fig. 9.5).

Although pleomorphic adenoma is a benign tumor, it may recur locally if the thin capsule is interrupted during surgical resection. Most frequently, these relapses are multifocal and appear very hyperintense on T2-weighted sequences.

Salivary malignancies are infrequent, with muco- epidermoid and adenoid cystic carcinoma being the most common histologic types. CT and MR characteristics do not allow differentiation of a malignant from a benign lesion, only the presence of inﬁ ltration of adjacent structures suggests malignancy.

Much rarer neoplasms in the prestyloid compartment are lipomas (Kakani et al. 1992) and muscular

neoplasms (rhabdomyomas and rhabdomyosarco- mas).

Anomalies of the second branchial apparatus rep- resent a spectrum of manifestations, ranging from a fi stula to an isolated cyst. One end of the spectrum is a fi stula between the anterior side of the sternocleidomastoid muscle and the pharyngeal wall at the level of the palatine tonsil. The other end of the spectrum is a cyst, potentially localised anywhere along this tract. The most typical localisation of such a cyst is just below the mandibular angle, posterior to the submandibular salivary gland, lateral to the vessels and anterior to the sternocleidomastoid muscle. As the trajectory of such a branchial apparatus anom- aly runs through the PPS, such cysts may also occur within the PPS (Fig. 9.6). Thickened, irregular walls may be seen in branchiogenic cysts that are, or have been infected. In the absence of a history of infl am- mation, an atypical cystic lesion should also raise the possibility of a cystic (retropharyngeal) adenopathy, as can be seen with papillary thyroid carcinoma (Fig. 9.7) (Lombardi et al. 2004).

A possible imaging pitfall in the prestyloid compartment is an hypertrophic pterygoid venous plexus mimicking a vascular lesion; in these cases imaging techniques will demonstrate the presence of multiple serpiginous ﬂ ow voids (on MR) or enhancing vessels (on CT) just medial to the medial pterygoid muscle.

Fig. 9.4a,b. Axial T2-weighted (a) and gadolinium-enhanced T1-weighted spin-echo image (b) in a patient with a coincidentally discovered PPS tumor. The lesion can not be separated from the deep lobe of the parotid gland (black arrow), and largely ﬁ lls the prestyloid compartment; a thin layer of fat is still visible at the anteromedial margin of the tumor (black arrowheads, b). The pharyngeal wall (white arrowheads) and medial pterygoid muscle (white arrow) are displaced. The large vessels (curved arrow) are displaced posteriorly. The styloid musculature produces an indentation in the posterior tumor margin (black arrowhead, a). The tumor was removed via a cervical approach, with resection of the deep parotid lobe. Pathologic examination showed pleomorphic adenoma

a b

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Fig. 9.5. Axial plain T1-weighted spin-echo image in a patient with a peritonsillar swelling on the right, rapidly increasing over a few hours time. A soft tissue mass (asterisk) is seen in the pre- styloid compartment of the PPS; the mass periphery, mainly on the tonsillar side, shows spontaneous hyperintensity, compatible with recent hemorrhage (arrows). The mass was resected;

pathologic examination showed pleomorphic adenoma

Fig. 9.6. A 3-year-old patient presenting with peritonsillar swelling. Axial T2-weighted spin-echo image shows a cystic mass in the prestyloid compartment of the PPS, displacing the pharyngeal wall. The cyst was resected and conﬁ rmed to be a branchiogenic cyst

Fig. 9.7a,b. An asymptomatic, 42-year-old female patient, with coincidentally discovered peritonsillar swelling on right side.

Axial T2-weighted (a) and gadolinium-enhanced T1-weighted (b) spin-echo images show largely cystic lesion, ﬁ lling the pre- styloid compartment of the PPS. The mass is centered between the prevertebral muscle (black arrowhead) and internal carotid artery (white arrowhead), a typical localisation for retropharyngeal adenopathy. The internal carotid artery, as well as the internal jugular vein (white arrow) are displaced posterolaterally. The cystic mass contains a solid component (black arrow), showing enhancement. A lesion showing such appearance, especially in a young female patient, should raise the possibility of metastatic papillary thyroid cancer. Cytologic examination of the cyst content was compatible with (although not conclusive for) metastatic papillary thyroid cancer. Resection of the thyroid gland eventually conﬁ rmed papillary cancer in the right lobe;

after subsequent resection of the retropharyngeal mass, metastatic thyroid cancer was histologically proven also at this level

a b

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9.3.2.2

Retrostyloid Lesions

A retrostyloid tumor can easily be identiﬁ ed when an anterior displacement of the ICA, and possibly the styloid process, is present. These lesions also displace the prestyloid PPS fat anteriorly. The most common primary lesions in this compartment are neurogenic tumors (17%–25% of all PPS neoplasms) and paragangliomas (10%–15%).

Schwannomas more frequently arise from the vagal nerve or from the cervical sympathetic chain.

Malignant degeneration has seldom been reported (Al Otieshan et al. 1998). The typical MR appearance of a schwannoma is that of an ovoid mass with a slightly hyperintense signal on T2-weighted images;

the lesion can be inhomogeneous because of areas of hemorrhage or cystic degeneration (Fig. 9.8). After the administration of a contrast agent, marked enhancement may lead to a misdiagnosis of a hypervascular tumor. Actually, a schwannoma is a relatively hypovascular lesion and the enhancement is due to extravascular leakage through abnormally perme- able vessels with poor venous drainage (Fig. 9.9).

Less frequent are neuroﬁ bromas, in 10% of cases associated to von Recklinghausen syndrome (Tandon et al. 1992). These lesions may undergo marked fatty replacement.

Paragangliomas arise from chemoreceptor cells, basically present at three different anatomical sites:

at the level of the nodose ganglion of vagal nerve, just below the skull base (vagal paraganglioma), at the ca-

rotid bifurcation (carotid paraganglioma) and at the level of the jugular foramen (jugular paraganglioma).

A marked enhancement and, at MR, a ‘salt and pepper’

pattern are quite typical: this is due to the presence of tortuous large caliber vessels (detected as ﬂ ow voids) within the mass (Fig. 9.10). Nevertheless, this pattern can be difﬁ cult to see or even absent, particularly in small lesions with predominantly small caliber feeding vessels (Fig. 9.11) (Som and Curtin 1995).

Carotid body tumors typically splay the internal and external carotid artery and may extend superiorly in the PPS. A vagal glomus tumor has a prevalent extracranial growth and only rarely reaches the carotid bifurcation. A jugular paraganglioma is centered in the jugular foramen, often eroding the surrounding bone and extending into the middle ear (Swartz et al. 1998). CT and MR allow an accurate diagnosis of glomus tumors in most cases; the role of angiogra- phy is restricted to accurate assessment of the arterial feeders and to preoperative embolization.

Several vascular anomalies may be encountered in the retrostyloid compartment. Sometimes the ICA shows a tortuous course, running behind the posterior pharyngeal wall: correct assessment avoids a disas- trous biopsy of a misinterpreted submucosal pharyngeal lesion. An occlusion of ICA, or a IJV thrombosis, are uncommonly encountered: MR shows a complex pattern of signal intensities of the intraluminal clot reﬂ ecting the different phases of hemoglobin deg- radation. MR is an accurate technique to diagnose dissection of the ICA. Aneurysms of the extracranial part of the ICA occur; rarely these aneurysms cause

Fig. 9.8a,b. T2-weighted (a) and gadolinium-enhanced T1-weighted (b) spin-echo images, showing a inhomogeneous mass in the retrostyloid compartment of the PPS, displacing the internal carotid artery (arrowhead) anteromedially, and the internal jugular vein (arrow) posterolaterally. Vagal schwannoma

a b

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to carefully assess its relationships with the PPS fat and large vessels. A neoplasm of the masticator space displaces this fat plane posteromedially (Fig. 9.13), while a tumor of the pharyngeal mucosal space will usually inﬁ ltrate the retrostyloid compartment (Fig. 9.14), displacing the fat tissue laterally. A retropharyngeal lesion (most often a retropharyngeal adenopathy) displaces the fat of the PPS anterolaterally (Fig. 9.15).

Fig. 9.9a–d. Axial T2-weighted (a), axial plain T1-weighted spin-echo image (b), gadolinium-enhanced 3D-gradient echo T1- weighted sequence, reformatted in oblique axial (c) and sagittal (d) plane. Solid mass lesion in the right PPS: anterior displacement of the internal carotid artery (black arrows) and stylopharyngeal muscle (arrowheads) indicates the retrostyloid compartment as the site of origin. T2 hyperintensity and bright enhancement (in the absence of vascular ﬂ ow voids) are consistent with neurogenic tumor. Tumor extension within the condylar canal (white arrow) along with denervation atrophy of the right hemitongue (asterisk) suggests schwannoma of the XIIth cranial nerve (hypoglossal nerve). The diagnosis was conﬁ rmed at surgery

a b

c

d

cranial nerve palsy. The diagnosis of such an aneurysm is usually straightforward (Fig. 9.12).

9.3.2

Secondary Lesions of the Parapharyngeal Space The key to correctly identify the site of origin of a lesion arising from a space neighbouring the PPS, is

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Fig. 9.10. Axial gadolinium-enhanced T1-weighted spin-echo image. A strongly enhancing mass, showing intratumoral signal voids, is present in the retrostyloid compartment of the PPS. The internal carotid artery is displaced anteromedially (arrowhead); the internal jugular vein is compressed and dis- placed posteromedially, not clearly identiﬁ able on this image.

(Image courtesy of Bert De Foer, MD, Antwerp, Belgium)

Fig. 9.12. Axial contrast-enhanced CT image shows nodular lesion in the retrostyloid compartment of the PPS. At fi rst sight one may think about retropharyngeal adenopathy. However, the narrowed lumen of the internal carotid artery (white arrowhead) is within the peripheral part of the mass, which also shows some peripheral calcifi cations (black arrowhead): these fi ndings are compatible with an internal carotid artery aneurysm

Fig. 9.11a–c. Gadolinium-enhanced 3D gradient-echo T1- weighted sequence in axial plane. Bilateral retrostyloid PPS mass (a,b): on the right side the internal carotid artery is anteromedially displaced (white arrows), and the stylopha- ryngeal muscle is anteriorly displaced (white arrowhead); on the left, anterior displacement of internal carotid artery is more evident (black arrow). Serpiginous ﬂ ow voids are more clearly demonstrated at the periphery of the left lesion, prob- ably due to its larger size. More caudally (c), a third lesion is demonstrated just medial to internal (i) and external (e) carotid artery, few millimetres above carotid bifurcation. MR ﬁ ndings are consistent with bilateral vagal paraganglioma and right carotid body tumor; this diagnosis is also strongly supported by a familial history for paraganglioma

a b

c

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Fig. 9.14. Patient presenting with increasing left-sided neck and facial pain. Axial gadolinium-enhanced T1-weighted spin- echo image shows poorly deﬁ ned, partially liqueﬁ ed mass in the left PPS, mainly within the retrostyloid compartment. The adjacent pharyngeal wall (arrow) appears inhomogeneous, with disruption of the constrictor muscle. Anterolateral displacement of the internal carotid artery (arrowhead), as well as of the prestyloid fat plane. Involvement of the prevertebral and paraspinal compartment is seen. Pharyngeal biopsy showed squamous cell cancer

Fig. 9.13a,b. Axial T2-weighted (a) and plain T1-weighted spin-echo image (b) in a 22-year old patient presenting with hearing loss on left side and increasing difﬁ culties with mastication. A soft tissue mass (black arrows) is seen on the deep side of the mandible, extending into the PPS; a thin layer of fat can be recognized on the posteromedial side of the mass (white arrow).

The lesion involves the deep lobe of the parotid gland. Contrary to the patient shown in Fig. 9.4, the pterygoid musculature can not be recognized anymore, suggesting that the point of origin is within the masticator space. Fluid is present in the mastoid, secondary to dysfunction of the eustachian tube. Biopsy revealed rhabdomyosarcoma

a b

Fig. 9.15. Axial contrast-enhanced CT image at level of naso- pharynx. Centrally necrotic retropharyngeal adenopathy (lymphatic metastasis of recurrent laryngeal cancer). A retropharyngeal adenopathy is typically situated between the prevertebral muscle (arrowhead) and the internal carotid artery (arrow); large adenopathies, such as in this case, displace the prestyloid fat anterolaterally

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Fig. 9.16a–c. T2-weighted spin-echo (a), plain (b) and gadolin- ium-enhanced T1-weighted spin-echo (c) images in the axial plane. Recurrent lymphangioma. The patient had received surgery 1 year before, as demonstrated by skin retraction (white arrowhead) and deep scar tissue in the proximity of external and internal carotid artery (black arrow). Residual lymphan- gioma is demonstrated in the PPS medially extending to the pharyngeal mucosal space (tonsillar fossa, base of tongue) (white arrows). The lesion shows bright T2 signal, no signifi - cant enhancement is observed after contrast application. The diagnosis was confi rmed with fi ne needle aspiration under ultrasound guidance

a b

c

Large and aggressive neoplasms, such as sometimes seen with sarcoma, nasopharyngeal cancer or lymphoma, may show a transspatial growth pattern;

in such circumstances, a precise diagnosis on imaging studies is not possible.

Secondary involvement of the parapharyngeal space may also be observed in benign multicom- partmental lesions, i.e. lesions characterized by the aptitude to grow across the boundaries that separate the deep spaces of the head and neck, thus invading simultaneously more than two compartments.

Among these, hemangioma and lymphangioma exhibit a rather peculiar imaging pattern consist- ing of hypodensity on plain CT and hyperintensity

on T2-weighted MR sequences. Dotted calciﬁ cations – better demonstrated on CT – may be seen in hemangiomas; MR may reveal serpiginous ﬂ ow voids representing dilated vascular channels. On the other hand, lymphangioma may exhibit spontaneous T1 hyperintensity, due to highly hyperprotein- aceous or fatty content. Contrast agent application better differentiates the two entities: hemangioma shows bright (though frequently non-homoge- neous) enhancement; lymphangioma, on the other hand, shows no contrast uptake, though enhancement of the multiple subtle septa crossing the lesion is occasionally observed (Figs. 9.16 and 9.17) (Sigal 1998).

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Parapharyngeal abscess is a rare event in the era of broad spectrum antibiotics, generally secondary to head and neck infections (odontogenic, pharyngeal, tonsillar, otomastoideal, or of salivary origin). On CT and MR, the detection of a fl uid fi lled cavity lined by an enhancing peripheral rim rather safely indicates the presence of an abscess, whereas a soft tissue swelling associated with non-homogeneity and ef- facement of fat planes suggests cellulitis. Actually, the discrimination between the two entities, potentially critical for treatment planning, may be hampered by a signifi cant number of false positives, particularly when cellulitis must be differentiated from an early abscess (Elden et al. 2001). Imaging also plays a key role in detecting major complications, more commonly occurring when the infectious process involves the retrostyloid compartment, such as IJV thrombosis, skull base osteomyelitis or extension in the retropharyngeal space (Nicolai et al. 2005).

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