Resolution of acquired tonsillar herniation after resection of supratentorial meningioma. Case illustration.

Abstract

This 51-year-old woman presented with neck pain, right homonymous hemianopsia, weakness, hyperreflexia, and extensor plantar responses. A magnetic resonance (MR) study demonstrated a large left parietooccipital meningioma without hydrocephalus (Fig. 1 left). We observed herniation of the cerebellar tonsils to C-1, with obliteration of the subarachnoid space (Fig. 1 center), which we believed was responsible for the patient’s symptoms. A left parietooccipital craniotomy was performed for gross-total resection of the meningioma with the patient prone. Somatosensory evoked potentials (SSEPs) were used to assess spinal cord function because of concern about head position and prolonged immobilization in the presence of tonsillar herniation. The SSEPs decreased significantly after the patient’s head was placed in the initial (neutral) position, and then recovered with moderate flexion of the patient’s neck from the neutral position. The patient made an uneventful recovery, with resolution of her symptoms. Her neck and occipital pain were markedly improved. A follow-up MR image demonstrated complete resection of the meningioma with ascent of the cerebellar tonsils to the level of the foramen magnum (Fig. 1 right). Acquired tonsillar herniation in adults has been well documented in conjunction with tumors, hydrocephalus, intracranial hypertension, serial lumbar punctures, and lumboperitoneal shunt placement. 1‐5 This syndrome has been called the “acquired Chiari I malformation.” In the present case, treatment of the supratentorial tumor resulted in reduction of the tonsillar herniation as seen on radiography, with clinical resolution of the neck pain and spasticity attributed to medullary compression. Posterior fossa decompression was not necesssary in this patient. We recommend that the intracranial pathology be treated first in similar cases, with radiographic imaging 3 to 6 months postoperatively to document any changes in tonsillar position. If possible, head and neck position should be maintained in neutral alignment during surgery. Spinal cord monitoring using SSEPs is critical to confirm safe intraoperative positioning.