The imaging demonstrates a lesion in Meckel's cave that is low on T1, dark on T2 and enhances. There is denervation atrophy of the pterygoid muscles on the right and opacification of the right mastoid air cells.
With imaging like this, you need to think of peritumoral spread along the cranial nerves. This is an odd example in that biopsy revealed Lymphoma.
- Perineural spread - tumor or other pathology spreads along tissues of neural sheath
- Common in head and neck cancer
- In head and neck cancer - major negative prognostic indicator
- Most common malignancies - salivary, mucosal and cutaneous
- Adenoid cystic frequently spreads by perineural tumor spread
- SCC of mucosal and cutaneous can
- Desmoplastic melanoma is common
- Often present at time of diagnosis; rarely present prior to detection
- Can present as recurrence or occur at the same time as recurrence
- Common hx - new cranial neuropathy
- Any tumor that are adjacent the skull base foramina are at risk of Perineural tumor spread; esp - masticator space, Meckel's cave, cavernous sinus and Pterygopalatine fossa
- Perineural spread - can be retrograde (toward CNS) or antegrade (away from CNS)
- Benign - some benign disorders spread along cranial nerves (essentially like PNS or similar to it by imaging) - schwannoma/neurofibroma, meningioma, rhinocerebral mucormycosis, sarcoidosis etc.
- Signs and Symptoms - pain and paresthesias
- V3 - weakness and denervation of muscles of mastication
- Facial - variable weakness or paralysis
- Most commonly affected - trigeminal and facial
- V2 (maxillary) and V3 (mandibular) - most common branches of CN V involved
- V1 - sensory to eye, lacrimal gland, conjunctiva, some nasal mucosa and upper face
- V1 - often from cutaneous lesion in supraorbital region; rare for intraorbital process to spread to V1
- V2 - sensory to mid and upper lateral face, mucosa of palate, sinonasal region, maxillary gingiva and maxillary teeth
- V2 - to spread along V2 from nasopharynx - must access pterygopalatine fossa (PPF) - often by nasal cavity then sphenopalatine foramen
- V2 - from skin along maxillary distribution - infraorbital nerve or zygomatic nerve
- Pterygopalatine fossa - Pterygopalatine ganglion, internal maxillary artery; bounded posteriorly by pterygoid plates, medially by palatine bone, anteriorly by maxillary sinus
- PPF - communicates laterally with infratemporal fossa with pterygomaxillary fissure
- PPF - communicates w/ intracranial space by foramen rotundum
- PPF - communicates with nasal cavity (medially) via sphenopalatine foramen
- PPF - Vidian nerve provides preganglinonic parasympathetic component of pterygopalatine ganglion
- PPF - communicates with greater and lesser palatine foramina inferiorly through the palate
- V3 - sensory innervation to skin of lower face and pre-auricular/temporal region, mandibular teeth, mucosa of mandibular gingiva, floor of mouth, ant 2/3 of tongue, buccal mucosa
- V3 - motor to musscles of mastication, mylohyoid and anterior digastric
- V3 - PNS - travel through foramen Ovale to Meckel's cave
- Facial Nerve (CN VII) - typically only 2 branches are affected - descending facial nerve (from parotid malignancies or lesions that involve the parotid) and the GSPN (greater superficial petrosal nerve)
- Descending facial nerve - can travel to geniculate ganglionand even through labyrinthine segment to involve internal auditory canal
- GSPN - small branch that leaves geniculate ganglion and exits superior surface of temporal bonte through facial hiatus to become intracranial; courses anteromedially beneath Meckel's cave to foramen Lacerum to join deep petrosal nerve (carotid sympathetic plexus) and become the Vidian nerve through Vidian canal
- Imaging - minimum need axial T1, axial T2, and 3 plane postcon T1 (with at least one in fat-suppressed form)
- T1 - look for loss of normal fat
- Look for widening of foramina - foramen ovale, mandibular foramen, foramen rotundum, PPF, foramen and canal for infraorbital nerve, vidian canal, palatine foramen, stylomastoid foramen, descending facial canal
- Look for enhancement
- Look for involvement of Meckel's cave
- Indirect findings - denervation of masticator muscles, anterior digastric, mylohyoid
- Early denervation - T2 bright and enhancement with post con
- Late - atrophy and fatty infiltration
Reference - MR Imaging of Perineural Tumor Spread by Lawrence E. Ginsberg; Neuroimaging Clinics of North America 14 (2004) 663-667
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