Teaching Case

Casual finding in an asymptomatic young woman.

A 29-year-old female patient presented with a solid mass in a CT performed for cranial traumatism outside our institution. The woman had no symptoms or surgical history. MRI was performed in order to characterize the lesion.
Unenhanced T1-weighted spin-echo MR images revealed a hypointense oval mass located in the right parapharyngeal space, the mass was well delineated and displaced the jugular vein laterally and posterior.
On T2- weighted spin-echo MR images the mass was hyperintense and heterogeneous.
On enhanced T1-weighted spin-echo MR image the mass enhanced strongly and homogeneously except for the centre of the mass.
There were no other lesions, enlarged lymph nodes, signs of peripheral infiltration or bone destruction.
The mass was surgically removed, with a final histological diagnosis of neurinoma, given its location in the anterior PPS, likely of trigeminal nerve origin.

The parapharyngeal space (PPS) is a deep neck space, shaped like an inverted pyramid: the skull base superiorly, and the hyoid bone inferiorly [1].
The medial aspect is made up by the pharynx; anteriorly the pterygomandibular raphe and posteriorly cervical vertebrae and paravertebral muscles.
The lateral aspect is bordered by the mandible, the parotid gland, medial pterygoid muscle and posterior belly of the disgastric muscle.
The PPS is divided in two parts - anterior and posterior - by the tensor-vascular-styloid fascia connecting the tensor veli palatini muscle with the styloid process [1].
This anatomical knowledge is important because masses with origin in the anterior PPS displace the posterior compartment (carotid space) posteriorly and laterally [2]. Precise localisation of a lesion narrows down the differential diagnosis.
The prestyloid PPS (anterior compartment) includes: branches of the mandibular division of the V nerve, internal maxillary artery, ascending pharyngeal artery, pharyngeal venous plexus and minor or ectopic salivary glands. Primary pathology derives from these structures [1]: trigeminal nerve schwannomas, maxillary artery aneurysms, and malignant and benign tumors originating from ectopic salivary tissue.
The poststyloid PPS (posterior compartment) includes the ICA (internal carotid artery), IJV (internal jugular vein), lymph nodes, the IX and XII cranial nerves, and sympathetic chain [1]. The most frequent pathology are adenophaties, although we should keep in mind paragangliomas and neural tumors.
The displacement of adjacent spaces allows to differentiate the origin of a mass in the PPS; a mass of the PPS is expected to displace the visceral space medially, the submandibular space infero-posterior, the masticator space anterolaterally [2].
The differentiation between anterior and posterior PPS masses, especially between trigeminal and glossopharyngeal schwannomas, remains in two clues:
1. Position of the styloid process
2. Posterior displacement of carotid space in anterior masses and anterior
displacement of fat in posterior masses
Schwannomas of the cervical sympathetic chain, that is lying posteromedial to the carotid vessels and is included in the posterior PPS, routinely displace the ICA anteriorly or anterolateraly, but have been reported to occasionaly replace the ICA posteriorly as well [3].
On the other hand extraadrenal paragangliomas (vagal), besides their location in posterior PPS, have a different radiological appearance with typical salt and pepper pattern.
The semiology of schwannoma and benign accessory salivary tumors located in the prestyloid PPS is quite similar and the final diagnosis is surgical.
Malignant tumors of anterior PPS have a more agressive radiological appareance, with ill defined borders and adenopathies.