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1 Downloaded from by on 02/06/18 from IP address opyright RRS. For personal use only; all rights reserved Imaging of Parapharyngeal Space Lesions: Focus on the Prestyloid ompartment T he parapharyngeal space is a deep potential neck space shaped as an inverted pyramid extending from the base of the skull to the hyoid bone. The differentiation of a prestyloid lesion from a poststyloid lesion is critical for guiding the surgeon in both the differential diagnosis as well as the potential surgical approach. Normal natomy The parapharyngeal space may be divided into two compartments on the basis of its relationship to the styloid process or, more precisely, to the tensor-vascular-styloid fascia (Fig. 1). The importance of the parapharyngeal space also lies in its relationship with the other spaces of the neck [1]. The masticator and parotid spaces are located laterally, the pharyngeal mucosal space is located medially, and the retropharyngeal space is located posteromedially (Fig. 1). The contents of the prestyloid compartment include the minor or ectopic salivary gland, branches of the mandibular division of the trigeminal nerve, internal maxillary artery, ascending pharyngeal artery, and pharyngeal venous plexus, whereas those of the poststyloid compartment include the internal carotid artery, internal jugular vein, cranial nerves IX XII, cervical sympathetic chain, and glomus bodies. Ji Hoon Shin 1, Ho Kyu Lee 1, Sang Yoon Kim 2, hoong Gon hoi 1, Dae hul Suh 1 ongenital or Developmental Lesions ranchial left yst The parapharyngeal space is a rare location for a branchial cleft cyst. The pharyngeal attachment and lack of deformity of the derivatives of the first branchial apparatus support the view that parapharyngeal space cysts originate in the second branchial apparatus. rapidly growing, infected branchial cleft cyst can present with lower cranial nerve palsies [2] (Fig. 2). ystic Lymphangioma (ystic Hygroma) Lymphangiomas form from errors in the development of the lymphatic system and can have variable vascularity [3]. Most lymphangiomas occur during early childhood because the greatest lymphatic development occurs between birth and 2 years. MR imaging usually shows the signal intensity of a multiloculated cystic lesion that does not displace adjacent soft-tissue structures because of the lesion s compressibility (Fig. 3). Neoplastic Lesions Tumors of the parapharyngeal space account for less than 0.5% of head and neck neoplasms [4]. However, various neoplastic lesions can involve the prestyloid parapharyngeal space. Intrinsic tumors are minor or Pictorial Essay ectopic salivary gland tumors and neurogenic tumors arising from the branches of the mandibular division of the trigeminal nerve. On the other hand, extrinsic tumors are most commonly parotid tumors of deep lobe origin, neurogenic tumors arising from the vagus nerve, or various tumors originating from the other surrounding spaces. Minor or Ectopic Salivary Gland Tumors Pleomorphic adenomas comprise the majority of minor or ectopic salivary gland tumors and are the most common neoplasms to originate in the prestyloid parapharyngeal space [5]. Malignant tumors, such as mucoepidermoid carcinoma or adenoid cystic carcinoma, are uncommon. Furthermore, several rare tumors, including basal cell adenoma, can originate from the minor salivary gland (Fig. 4). Preservation of the fat plane between the mass and the parotid gland strongly suggests an extraparotid origin. Neurogenic Tumors Neurogenic tumors are the second most common neoplasms originating from the prestyloid parapharyngeal space and are the most common poststyloid parapharyngeal space tumors. Most neurogenic tumors arise from the trigeminal nerve in the prestyloid parapharyngeal space and arise from the va- Received February 5, 2001; accepted after revision May 31, Department of Radiology, University of Ulsan ollege of Medicine, san Medical enter, Poongnap-Dong, Songpa-Ku, Seoul , South Korea. ddress correspondence to H. K. Lee. 2 Department of Otolaryngology, University of Ulsan ollege of Medicine, san Medical enter, Songpa-Ku, Seoul , South Korea. JR 2001;177: X/01/ merican Roentgen Ray Society JR:177, December

2 Shin et al. Downloaded from by on 02/06/18 from IP address opyright RRS. For personal use only; all rights reserved gus nerve in the poststyloid parapharyngeal space. In tumors arising from the poststyloid parapharyngeal space, anteromedial displacement of the carotid sheath structures is frequent because the vagus nerve and sympathetic chain are posterior to the internal carotid artery, whereas posterolateral displacement of the carotid sheath structures is frequent in tumors arising from the prestyloid parapharyngeal space [5]. Malignant peripheral nerve sheath tumors are rare, highly aggressive tumors capable of arising de novo or from preexisting benign neurofibromas or schwannomas; 25 75% of this type of tumor are associated with neurofibromatosis [6] (Fig. 5). D Tumors from the Other Surrounding Spaces Tumors of the skull base or tumors of the vertebrae, such as chordomas or meningiomas, can extend into the parapharyngeal space. Pharyngeal mucosal space lesions, such as nasopharynx carcinoma, may have extensive submucosal and parapharyngeal space extension. The most common extrinsic tumors involving the prestyloid parapharyngeal space are parotid tumors arising from the deep lobe of the parotid gland [5]. Pleomorphic adenomas are the most commonly encountered parotid gland tumors. Occasionally, a dumbbell shape is seen with the waist formation by the narrow stylomandibular tunnel in the deep Fig. 1. Normal anatomy of parapharyngeal space. S = buccal space, I = internal carotid artery, IJV = internal jugular vein, MS = masticator space, PMS = pharyngeal mucosal space, PPS = parapharyngeal space, PS = parotid space, PVS = prevertebral space, RPS = retropharyngeal space, SMS = submandibular space, T = torus tubarius., xial unenhanced T1-weighted spin-echo MR image obtained at nasopharynx level shows fat-filled prestyloid parapharyngeal space (asterisks) located between masticator space and pharyngeal mucosal space. Torus tubarius represents pharyngeal mucosal space at nasopharynx level. Poststyloid parapharyngeal space containing major neurovascular bundle of internal carotid artery and internal jugular vein is located posteriorly., xial unenhanced T1-weighted spin-echo MR image obtained at oropharynx level shows that parotid space containing parotid gland forms posterolateral boundary of parapharyngeal space (asterisks), and retropharyngeal space and prevertebral space form posteromedial boundary of parapharyngeal space (asterisks)., oronal unenhanced T1-weighted spin-echo MR image shows continuity of prestyloid parapharyngeal space (asterisks) with submandibular space. Pharyngeal mucosal space is located medially. D, xial schematic at nasopharynx level shows that parapharyngeal space is divided into prestyloid and poststyloid compartments by tensor-vascular-styloid fascia connecting tensor veli palatini muscle with styloid process. lobe parotid tumors. The loss of the fat line between the mass and the parotid gland suggests a deep lobe parotid origin (Fig. 6). Schwannomas and paragangliomas may arise in the poststyloid parapharyngeal space and extend into the prestyloid parapharyngeal space (Fig. 7). Infiltrative masses involving the parapharyngeal space are soft-tissue sarcomas of fatty, muscular, or fibrous origin, arising mainly from the adjacent spaces (Fig. 8). Usually, associated bone destruction is also present (Fig. 8). Rarely, astleman s disease, arising from the lymph nodes in the adjacent spaces, can involve the prestyloid parapharyngeal space [7] (Fig. 9) JR:177, December 2001

3 Imaging of Parapharyngeal Space Lesions Downloaded from by on 02/06/18 from IP address opyright RRS. For personal use only; all rights reserved Infectious or Inflammatory Lesions Most commonly, infections of the masticator space involve the parapharyngeal space and accompany medial displacement of the parapharyngeal space fat. Obliteration of the parapharyngeal space fat plane is also frequently associated with infections of the masticator space. Odontogenic infection is most commonly the source of an inflammatory mass in the masticator space and is frequently associated with facial swelling, pain, and trismus [5]. Fig. 2. Second branchial cleft cyst in 35-year-old woman with multiple lower cranial palsies that subsided after removal of lesion., xial enhanced T1-weighted spin-echo MR image shows well-marginated, nonenhancing mass that is slightly hyperintense to cerebrospinal fluid in right prestyloid parapharyngeal space, displacing internal carotid artery and internal jugular vein to its posterolateral side (arrow)., T2-weighted spin-echo MR image shows mass is slightly hypointense to cerebrospinal fluid. Displacement of internal carotid artery and internal jugular vein to its posterolateral side (arrow) can also be seen., Unenhanced coronal T1-weighted spin-echo MR image shows mass (arrowheads) occupying right parapharyngeal space from below skull base to upper level of submandibular gland. On aspiration, contents contained pus. Fig. 3. ystic lymphangioma in 2-year-old boy with left parotid area swelling., xial enhanced T1-weighted spin-echo MR image shows multiloculated, nonenhancing cystic mass (arrows) in left prestyloid parapharyngeal space and in left parotid space., xial T2-weighted spin-echo MR image shows hyperintense mass (arrows)., oronal short tau inversion recovery MR image clearly shows bilateral multiloculated cystic lesions (arrows). The pharyngeal tonsil and submandibular gland can be another source of infection involving the parapharyngeal space. ellulitis or abscess may form as a complication of acute tonsillitis or sialoadenitis (Fig. 10). On the contrary, infections may readily spread from the parapharyngeal space into other areas of the neck or extend via the retropharyngeal space into the upper mediastinum because of the parapharyngeal space s close attachment and free communication with the other neck spaces [8]. onclusion The majority of lesions, mostly tumors, involving the prestyloid parapharyngeal space are either neurogenic tumors or salivary gland tumors from the deep lobe of the parotid gland or from the minor salivary gland. y observing the direction of displacement or infiltration of the parapharyngeal space, internal carotid artery displacement, and presence or absence of the medial fat plane, it is possible to localize a lesion to one of several spaces in the neck [1, 5]. JR:177, December

4 Shin et al. Downloaded from by on 02/06/18 from IP address opyright RRS. For personal use only; all rights reserved Fig. 4. asal cell adenoma in 61-year-old woman with bulging mass on left oral cavity., xial unenhanced T1-weighted spin-echo MR image shows round, solid and cystic (peripheral high-signal-intensity) (asterisk) mass in left prestyloid parapharyngeal space. ystic contents were hemorrhagic on aspiration. Linear fat line between tumor and parotid gland (arrow) suggests extraparotid origin of tumor., xial T2-weighted spin-echo MR image shows signal intensity of mass is slightly increased. Linear fat line between tumor and parotid gland (arrow) can also be seen., oronal enhanced T1-weighted spin-echo MR image shows moderate enhancement of solid portion. D Fig. 5. Malignant peripheral nerve sheath tumor arising from trigeminal nerve in 35-year-old man with right tinnitus and hearing disturbance., xial unenhanced T1-weighted spin-echo MR image shows ovoid isointense mass (short arrows) in right prestyloid parapharyngeal space. Laterally displaced parapharyngeal space fat suggests its origin in prestyloid parapharyngeal space (long arrow)., xial T2-weighted spin-echo MR image shows tumor (arrows) is slightly hyperintense to muscle., xial T2-weighted spin-echo MR image shows tumor (arrows) extends into eustachian tube (arrowheads). D, oronal enhanced T1-weighted spin-echo MR image shows strong enhancement of mass (arrows). Foramen ovale is widened by tumor (arrowhead), suggesting its perineural extension JR:177, December 2001

5 Imaging of Parapharyngeal Space Lesions Downloaded from by on 02/06/18 from IP address opyright RRS. For personal use only; all rights reserved Fig. 6. Mucoepidermoid carcinoma of deep lobe parotid gland in 40-year-old man with left soft palate area swelling., ontrast-enhanced T scan shows inhomogeneously enhancing mass (asterisk) in left prestyloid parapharyngeal space. Stylomandibular tunnel (arrows) is widened by tumor, suggesting deep lobe parotid tumor. Medial fat line (arrowhead) between mass and pharyngeal mucosa is displaced but preserved., xial unenhanced T1-weighted spin-echo MR image shows low-signal-intensity mass (asterisk). Medial fat line (arrowhead) between mass and pharyngeal mucosa is displaced but preserved, whereas lateral fat line between mass and parotid gland is not seen, indicating parotid origin., xial enhanced T1-weighted spin-echo MR image shows inhomogeneously enhancing mass (asterisk). Preservation of medial fat line (arrowhead) between mass and pharyngeal mucosa can also be seen. Fig. 7. Paraganglioma in 61-year-old woman with left submandibular area swelling., xial unenhanced T1-weighted spin-echo MR image shows slightly inhomogeneous low-signal-intensity mass in left parapharyngeal space. nteromedial displacement of internal carotid artery (arrow) indicates poststyloid parapharyngeal space origin of tumor., xial T2-weighted spin-echo MR image shows slightly inhomogeneously hyperintense mass. nteromedial displacement of internal carotid artery (arrow) can also be seen., oronal enhanced T1-weighted spin-echo MR image shows location of tumor on carotid bifurcation with clear splaying of internal and external carotid arteries (arrowheads). These findings are highly specific for carotid body tumor. Fig. 8. Rhabdomyosarcoma in 10-year-old boy with left infraauricular area swelling., xial unenhanced T1-weighted spin-echo MR image shows lobulated, bulky low-signal-intensity mass involving left masticator, parotid, prevertebral, and parapharyngeal spaces. Medial margin of mandible (arrow) was partially destroyed by tumor., xial enhanced T1-weighted MR image shows inhomogeneous dense enhancement. Partial destruction of medial margin of mandible (arrow) is also seen. JR:177, December

6 Shin et al. Downloaded from by on 02/06/18 from IP address opyright RRS. For personal use only; all rights reserved Fig. 9. astleman s disease arising from retropharyngeal space in 34-year-old woman with painless swelling on right side of oropharynx., xial unenhanced T1-weighted spin-echo MR image shows well-marginated, isointense mass in right parapharyngeal space. Parapharyngeal space fat is displaced anteriorly (short arrow), and posterolateral displacement and separation of internal and external carotid arteries are seen (long arrows)., xial T2-weighted spin-echo MR image also clearly shows posterolateral displacement and separation of internal and external carotid arteries (arrows). Linear hypointense signal is seen in mass (arrowheads), which was revealed to be perivascular lamellar fibrosis on pathologic correlation., oronal enhanced T1-weighted spin-echo MR image shows moderate enhancement of mass. References 1. hong VF, Fan YF. Radiology of the parapharyngeal space. ustralas Radiol 1998;42: Shin JH, Lee HK, Kim SY, et al. Parapharyngeal second branchial cleft cyst manifesting as cranial nerve palsies: MR findings. JNR 2001; 22: Mra Z, Emami J, Simpson GT II. Parapharyngeal lymphangioma mimicking a peritonsillar abscess. Ear Nose Throat J 1996;75: atsakis JG, Sneige N. Parapharyngeal and retropharyngeal space diseases. nn Otol Rhinol Laryngol 1989;98: Tom M, Rao VM, Guglielmo F. Imaging of the parapharyngeal space: anatomy and pathology. rit Rev Diagn Imaging 1991;31: Lee JH, Lee HK, hoi G, Suh D, Lee KS, Khang SK. Malignant peripheral nerve sheath Fig. 10. bscess associated with sialoadenitis of submandibular gland in 33-year-old woman with painful swelling of left submandibular area., ontrast-enhanced T scan shows abscess formation with air in left parapharyngeal space (arrows)., ontrast-enhanced T scan obtained from lower level clearly shows left submandibular gland enlargement (arrowheads) with surrounding fluid collection. tumor in the parapharyngeal space: tumor spread through the eustachian tube. JNR 2001; 22: Shin JH, Lee HK, Kim SY, et al. astleman s disease in the retropharyngeal space: T and MR imaging findings. JNR 2000;21: ass RM. pproaches to the diagnosis and treatment of tumors of the parapharyngeal space. Head Neck Surg 1982;4: JR:177, December 2001