Overshunting-Associated Myelopathy: Flattened Spinal Cord Compressed By Epidural Venous Plexus

A 50-year-old woman presented with a 1-month history of progressive spastic quadriparesis. She had undergone nonprogrammable ventriculoperitoneal (VP) shunt placement after intraventricular hemorrhage due to a ruptured arteriovenous malformation 16 years previously. Neurologically, she had neck extensor weakness (Medical Research Council [MRC] grade 4), symmetrical weakness of her upper extremities (right/left MRC grades 4/4), and weakness of her right proximal lower extremity (MRC grade 4). She also had spasticity and hyperreflexia in all 4 extremities with extensor plantar reflexes. Light touch and vibratory sensation was impaired in the right distal lower extremity. Neck MRI demonstrated that the cervical spinal cord was compressed from both sides by an engorged epidural venous plexus (figure 1). Brain MRI revealed diffuse pachymeningeal enhancement and slit ventricles. Overshunting-associated myelopathy (OSAM) was diagnosed. Her symptoms resolved completely 3 months after VP shunt revision (figure 2).