Presentation
The patient presented with vertigo, ataxia, and a right third nerve palsy.
Patient Data
Multiplanar and multiaxial MR imaging confirmed the presence of a large right trigeminal schwannoma.
Typical intermediate-to-low T1 signal intensity and associated intermediate-to-high T2 signal intensity. Heterogeneous appearance on SWI, suggesting intralesional hemorrhage. No evidence of diffusion restriction, with shine-through artifact. Avid heterogeneous post-contrast enhancement.
The lesion presents as a tri-lobular extra-axial space-occupying lesion straddling the posterior and middle cranial fossae and the right infratemporal fossa. Specifically, the lesion straddles the right cerebellopontine angle (CPA) cistern, arising from the nerve root entry zone to Meckel's cave and further extends into the right infratemporal fossa and masticator space.
It is multifocal, consisting of preganglionic, ganglionic, and postganglionic segments, with consequent trilobular shape. There is no intracanalicular extension within the right internal auditory canal (IAC). Significant asymmetric mass effect on the midbrain, pons, and superior medulla with no associated edema or ischemia. Mass effect on the third ventricle and Sylvian aqueduct; however, no obstructive hydrocephalus. Displacement and asymmetry of the optic chiasm and hypothalamus.
Displacement of the basilar artery towards the left, draping of the right posterior cerebral artery (PCA) and the right posterior communicating artery (PCom). No vascular encasement or regional thrombosis.
Abutment to the right petrous intracranial internal carotid artery within the infratemporal fossa; however, with no encasement or thrombosis.
Cystic component present within the infratemporal fossa.
The lesion measures:
Cisternal: 30.1x 30.8x 39.5 mm's (oblique ap x oblique width x craniocaudal)
Right temporal: 29.3x 27.8x 30.1 mm's (oblique ap x oblique width x craniocaudal.)
Infratemporal: 23.7x 19.1x 17.4 mm's ( oblique ap x oblique width x craniocaudal).
Contrast-enhanced MR Imaging of the brain is otherwise normal. Specifically, no vestibular schwannomas bilaterally, no meningiomas and a normal left cavernous sinus.
Images with a superimposed dumb-bell demonstrate the waisting at the porus trigeminus and foramen ovale.
Histology:
The H&E stains confirm typical Antoni A (highly cellular with nuclear palisading) and Antoni B (hypocellular) areas with hyalinised and thrombosed vessels consistent with a benign spindle cell neoplasm (schwannoma). No atypia or mitotic activity was present.
Appropriate immunohistochemical stains have been performed on the tissue submitted and in the presence of adequate and positive controls, these stains have proved as follows:-
1. S100 protein – strongly positive in the spindle cell proliferation with both nuclear and cytoplasmic positivity present supporting the morphological diagnosis of a schwannoma
2. GFAP (Glial Fibrillary Acidic Protein) – shows some background staining but the impression is that this represents a population of reactive astrocytic cells
3. CD34 – negative
4. SMA – negative, although prominent staining of blood vessel
5. MSA – negative
6. Ki-67 – very low proliferative index, mainly staining up into the interwoven inflammatory cells
COMMENT: Overall, the immunohistochemical features, particularly the strong diffuse S100 positivity within the lesional cells is supportive of a diagnosis of a trigeminal nerve neurilemmoma/schwannoma.
Histology: Dr SJ NAYLER MB BCh (Wits), MMed (Wits), FC Path (SA)
(Drs Gritzman and Thatcher Inc, Randburg, South Africa)
The MRI study post first surgical resection/debulking demonstrates residual tri-lobular trigeminal schwannoma with a reduced volume of the cisternal or preganglionic segment in the right CP angle. Reduced but persistent regional mass effect on the brainstem. Post-surgical intralesional hemorrhage evident on T1WI and SWI. There is blooming on SWI along the surgical tract from the posterior fossa craniotomy. The ganglionic and postganglionic segments appear static and untouched. The mass effect on the optic chiasm, the hypothalamus, third ventricle and aqueduct is reduced and no progressive obstructive hydrocephalus is present. The diffusion study remains normal post-surgery.
New right mastoid effusion.
Case Discussion
This young female patient presented to the ophthalmologist due to a third nerve palsy (diplopia/ptosis/dilated pupil) with a history of acute progressive ataxia and vertigo. These symptoms are due to the mass effect of the large trigeminal schwannoma on the midbrain, pons and medulla and additionally, due to mass effect within Meckel's cave affecting the right third cranial nerve.
The lesion has a waist at the porus trigeminus, giving rise to the typical dumb-bell shape of a bi-lobed lesion straddling the posterior fossa (CP angle) and middle cranial fossa (Meckel's cave/temporal lobe). In this instance, the lesion has a third lobule within the right infratemporal fossa (masticator space), and consequent additional waisting at the foramen ovale. This gives it a trilobular shape due to extension and spread along the course of the mandibular division (V3) of the right trigeminal nerve. This is well identified on the coronal and sagittal sequences.
Trigeminus means "thrice twinned" referring to the dual right and left nerve having 3 major branches (ophthalmic-V1, maxillary-V2 and mandibular-V3).
Multiple surgical attempts to excise/debulk the schwannoma are planned. The initial procedure was performed through a right posterior fossa craniotomy and there is a reduced volume of the cisternal component and significantly improved midbrain mass effect on the post-surgical follow up scan. There are expected post-surgical changes of intralesional and surgical tract hemorrhage. MRI brain is otherwise normal.
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