Large demyelinating lesions: a neurosurgical perspective

OBJECT/ BACKGROUND: Large demyelinating lesions (LDLs) may present with unusual features like seizures and significant mass effect and often masquerade a tumour. Even radiological features are confusing. With clinical signs of increased intra-cranial pressure (ICP), decompressive surgery becomes life-saving. However, resection of the involved nervous tissue is unnecessary and may lead to permanent residual deficits that otherwise can be avoided.

We present a series of eight patients with focal deficits and/or raised pressure symptoms wherein a diagnosis of tumour was made preoperatively. The clinico-radiological picture and outcome has been described.

Clinically, all these patients had focal deficits and five had raised ICP. Three patients had seizures. Two patients had long standing visual deterioration in one eye. Radiology showed irregular enhancement in two and concentric rings in one. The deep grey matter was involved in one and cortex in four. Biopsy/decompressive surgery and resection of lesion improved the sensorium in all, but focal deficits persisted. Two patients died after being discharged in a conscious state, and one died in hospital.

High index of suspicion is required to diagnose demyelination prior to surgery. Unexplained long standing clinical features, radiology that has contrast enhancement patterns and mass effect (dissociation between contrast enhancement and mass effect) that is unusual for glioma should raise the suspicion of such non-neoplastic lesions. For patients with minimal mass effect with focal deficits, open/stereotactic biopsy from multiple areas of the lesion is preferable for diagnosis. Those presenting with mass effect, decompressive craniectomy and biopsy from the lesion is preferable than attempting complete resection especially in and around the eloquent areas. A second look surgery to resect the lesion can always be undertaken once histopathology suggests a neoplastic etiology and rules out a demyelinating lesion.