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Mapping affected sites of cavernous malformation in the posterior cranial fossa

Dear Editor, Cavernous malformation (CM), previously called cavernous hemangioma or cavernoma, describes clusters of dilated sinusoidal channels lined by a single layer of endothelium. As the second most common intracranial vascular malformation after arteriovenous malformation, it represents 15% of all cases of cerebral vascular malformation. Intracranial is most common in the cerebral hemispheres, while the location of posterior cranial fossa accounts for 10–30% of intracranial cavernous malformations. Additionally, brainstem cavernous malformation may induce vertiginous attacks because of its close proximity to the cranial nerve VIII, resulting in pathological eye movements and ataxia. Although MR imaging can settle the question of posterior fossa involvement, it may overlook the minute brainstem lesion. Alternatively, the latter can be evaluated by the recently developed vestibular evoked myogenic potential (VEMP) test. Stimulation via air-conducted sound or bone-conducted vibration enables recording of vestibular evoked myogenic potential from the cervicalmuscles (called cervical vestibular evoked myogenic potential) and extraocular muscles (called ocular vestibular evoked myogenic potential). A recent investigation showed that the cervical vestibular evoked myogenic potential test assesses the sacculo-collic reflex, descending through the lower brainstem. In contrast, the ocular vestibular evoked myogenic potential test evaluates the vestibulo-ocular reflex, ascending through the upper brainstem. Clinically, the use of ocular and cervical vestibular evoked myogenic potential tests can help differentiate lesions between brainstem and cerebellum. Because cavernous malformation in the brainstem may cause recurrent bleeding, and because minute haemorrhagic foci in the brainstem may not be demonstrated by MR imaging, vestibular evoked myogenic potential testing thus helps identify brainstem integrity. This study applied a test battery comprising audiometry, caloric test and ocular and cervical vestibular evoked myogenic potential tests in patients with posterior fossa cavernous malformation to map affected sites.