Motor neuron disease-like syndrome secondary to trapped fourth ventricle and obstruction of cerebrospinal fluid pathway.

The trapped fourth ventricle is caused by occlusion of outlets of fourth ventricle, including cerebral aqueduct and foramina of Luschka and Magendie. It is an uncommon entity that mainly occurs in children with hydrocephalus after successful shunting of lateral ventricles. The most common etiologies of obstruction to outflow of the fourth ventricle are infection and hemorrhage. Typical manifestation of trapped fourth ventricle is posterior fossa syndrome. Here, we report a 22-year-old man with hydrocephalus developed after successful removal of traumatic subdural hemorrhage. After shunting of lateral ventricles, hydrocephalus resolved initially. However, trapped fourth ventricle occurred 9 months later. Unlike previous reports of trapped fourth ventricle, his presentation was motor neuron disease-like syndrome, including hand muscle weakness and atrophy, generalized brisk deep tendon reflexes, and absence of sensory deficits. Imaging study showed isolated dilatation of fourth ventricle and edema of cervical cord from obex to C7 level. After surgical decompression and lysis of adhesion of posterior fossa, neurological deficits well recovered. The pathogenesis of hand muscle atrophy is secondary to cervical cord edema caused by trapped fourth ventricle and obstruction of cerebrospinal fluid (CSF) pathway. Furthermore, the anterior horn cells and lateral corticospinal tract are located in the highly vulnerable region of spinal cord, either possibly due to venous engorgement or arterial insufficiency.