Differential involvement of brainstem pathways due to fourth ventricular epidermoid cyst: a case study.

A 66-year-old man presented with progressive dysfunction of bilateral cerebellar hemispheres or its connections, corticospinal tracts and medial longitudinal fasciculus (MLF) due to a 4th ventricular epidermoid cyst for the past 47 years. Sensory, auditory and blink reflex pathways were clinically and electrophysiologically normal as indicated by clinical examination and normal median nerve somatosensory evoked responses (SER), brainstem auditory evoked responses (BAER) and blink reflex (BR) studies. These findings were unchanged fifteen months after removal of the lesion. Our findings suggest that (1) in extraaxial brainstem compression, MLF dysfunction can occur, (2) MLF, corticospinal tracts and possibly cerebellum and its connections appear to be more susceptible to longstanding compression and can be selectively and irreversibly damaged whereas pathways located in their vicinity, subserving SER, BAER and BR are spared, and (3) normal clinical and electrophysiological examination of sensory, auditory and BR pathways in presence of abnormal MLF, corticospinal and cerebellar functions should raise a clinical suspicion of an extraaxial brainstem compressive lesion.