Keywords
vestibular schwannoma - facial nerve paresis - false localizing sign
Introduction
Vestibular schwannomas are the most common cerebellopontine angle tumors. These tumors
commonly present with ipsilateral dysfunction of acoustic, vestibular, trigeminal,
and facial nerves.[1] Presentation of the vestibular schwannoma with contralateral facial nerve dysfunction
is quite uncommon, and the contralateral facial paresis has been mentioned as a false
localizing sign for posterior fossa and cerebellopontine angle tumors.[2]
[3]
[4] Among 287 patients with vestibular schwannoma who underwent surgery at our institute
during past 8 years, we encountered one 1 patient with this unusual presentation.
Case Report
A 35-year-old woman presented with history of vertigo, progressive left-sided loss
hearing, and gait ataxia for 1 year, and headache, diplopia, and progressive asymmetry
of the face for 2 months. Neurologic examination showed bilateral grade 3 papilledema,
decreased left-sided corneal sensation, left-sided sensory-neural hearing loss, left-sided
delayed taste sensation, deviation of the face toward left side (House-Brackmann grade
3; right-sided facial palsy), and right-sided sixth nerve paresis ([Fig. 1]). Her cerebellar tests were abnormal on the left side. Magnetic resonance imaging
(MRI) showed a large ((39 × 37 × 39 mm) left cerebellopontine angle mass that appears
hypointense on T1W1 images and hyperintense on T2W1 images with heterogenous enhancement
on gadolinium administration ([Fig. 2A–C]). Hydrocephalus with periventricular lucency and distortion of the brainstem were
also seen. The radiologic impression was suggestive of vestibular schwannoma and the
patient was prepared for surgery.
Fig. 1 Bilateral grade 3 papilledema, decreased left-sided corneal sensation, left-sided
sensory-neural hearing loss, left-sided delayed taste sensation, deviation of the
face toward left side, and right-sided sixth nerve paresis.
Fig. 2 MRI showing a large (39 × 37 × 39 mm) left cerebellopontine angle mass.
A left retromastoid suboccipital craniectomy with near total excision of the lesion
was performed with preservation of facial nerve by using intraoperative nerve monitoring.
Postoperative recovery was uneventful, and postoperative computed tomographic (CT)
scan showed complete excision of the lesion. Histopathologic examination (HPE) of
the specimen confirmed the preoperative diagnosis of vestibular schwannoma. Postoperatively,
double vision subsided but right facial nerve paresis showed no improvement.
Discussion
False localizing signs are unexpected neurologic deficits based on anatomic location
and pathophysiologic processes.[5] Cranial nerve palsies, hemiparesis, sensory features, and muscle atrophy may all
occur as false localizing signs.[6] Review of literature showed various cranial nerve dysfunction as a false localizing
sign, including abducens nerve (most common), trigeminal nerve, facial nerve, vestibulocochlear
nerve, and oculomotor nerve.[2]
[3]
[4]
[5]
[6]
[7] Multiple cranial nerve dysfunction presenting as false localizing signs is very
rare. Concurrent involvement of the trigeminal sensory, abducens, and facial nerves
as false localizing signs was reported by Ro et al.[2] Involvement of both the facial and vestibulocochlear nerves as false localizing
signs was reported by Paillas et al.[3] Our case is distinct from these cases in that we report dysfunction of the contralateral
abducens and facial nerves as false localizing signs.
Multiple cranial nerve palsy associated with cerebellopontine angle and posterior
fossa tumors has been attributed to different factors such as the tumor size, raised
intracranial pressure (ICP), compression and distortion of the brainstem, angulations
and distortion of the nerve roots, and the relationships of cranial nerves and nearby
blood vessels. The direction of displacement is determined by the anatomic variations
of the bony surface and surrounding rigid structures.[8] According to Paillas et al, tumor size (large) and nature (firm) were responsible
for false localizing signs of cranial nerve.[3]
The abducens nerve palsy is most common cranial nerve dysfunction presented as false
localizing sign.[8] The abducens nerve dysfunction in cases of raised ICP was possibly caused by a posterior
shift of the brainstem and stretching of this nerve in its vertical course in a direction
opposite to the brain displacement.[5] The abducens nerve can also be entrapped or strangulated by the branches of the
basilar artery when the pons and medulla are distorted by the posterior fossa tumor.[9] However, it is difficult to determine which mechanism contributed to the clinical
presentation of our case (raised ICP and brainstem distortion both were present).
The facial nerve proper and intermediate and vestibulocochlear nerves leave the brainstem
and pass through the internal auditory meatus along a bony canal, which may make them
subject to compression on the margins of the meatus when the brainstem is displaced.[2] The nervus intermedius is a small bundle that usually leaves the pons closer to
the vestibulocochlear nerve than facial nerve proper and runs between them across
the cerebellopontine angle cistern, moving closer to facial nerve proper as it enters
the facial canal. In our case only the facial nerve proper but not intermediate or
vestibulocochlear nerve is involved as a false localizing sign. The variable vessel-facial
nerve and vessel-vestibulocochlear nerve relationships outside and inside the internal
meatus and the nearby blood vessels might compress or strangulate the nearby facial
nerve only when the brainstem is distorted.[10] In our case, there is a well-maintained cerebrospinal fluid (CSF) subarachnoid space
in right CP angle cistern ([Fig. 2D] asterisk) with no MRI evidence of compression of distorted brainstem onto the adjacent
petrous bone ([Fig. 2D]). Even the right seventh/eight nerve complex also appears intact. Hence a high possibility
of a vascular event in the form of ischemia or strangulation of the nerve by a vessel
loop explains the nonrecovering facial nerve deficit. However, cranial nerve anatomy
can be better delineated with special MRI sequences such as FIESTA/CISS (fast imaging
employing steady-state acquisition/constructive interference in steady state) (not
done in our case). Reports of false localizing seventh nerve palsies suggest that
they most often occur at the same time as, or after, the development of sixth nerve
palsies.[2]
[5]
[11] In our case both palsies were involved at the time of presentation, and hence the
exact cause cannot be ascertained.
Conclusion
Contralateral facial palsy is an extremely rare presentation of vestibular schwannomas
even with brainstem distortion. The causative mechanism is most probably displacement
and distortion of the brainstem, with or without a vascular pathology. A number of
factors are responsible for false localizing sign such as tumor size and consistency
raised ICP, compression and distortion of the brainstem, angulations and distortion
of the nerve roots, and the relationships of cranial nerves and nearby blood vessels.
