Meningocerebral hemangiomatosis resembling Sturge-Weber disease in a horse.

A 3-year-old horse presented with intermittent generalized seizures of 2-month duration. During interictal periods, the horse appeared normal and a cause for the seizures could not be identified. Necropsy revealed opacity of the leptomeninges, covering most of one cerebral hemisphere along with thinning and collapse of the cortex in the ipsilateral pyriform lobe. Histopathology demonstrated leptomeningeal vascular proliferation and meningothelial hyperplasia. Prominent tortuous vessels of the gyri and sulci extended into some regions of the subjacent cortex, where there was neuronal loss, ectopia, and disorganization. Clusters of prominent arterioles were found in the sclerotic choroid plexus of the lateral and fourth ventricles. Milder vascular lesions were present in the leptomeninges of the ventral brain stem, right cerebrum, spinal cord, and in the eye. The left trigeminal nerve was distorted by swollen fasicles containing onion bulb-like structures. Most bulbs contained central axons surrounded by myelin sheaths of variable thickness. Electron microscopy demonstrated concentrically arranged cells with continuous basal laminae and rare pinocytotic vesicles. S-100 immunohistochemistry showed strong positive staining in these cells. This is an unusual combination of lesions to which analogies can be drawn with the human neuroectodermal dysplasias, specifically Sturge-Weber disease. The relationship of the neuropathy to the leptomeningeal hemangiomatosis is unclear, but a compound anomaly in embryological development resulting in dysplasia and neoplasia may be involved.