Lumbosacral perineural cysts as a cause for neurogenic muscular hypertrophy.

We report the case of a 40 year-old man with a severe lesion of the anterior rami of the left spinal nerves L5 and S1 who showed hypertrophy of the leg and atrophy of the intrinsic foot and gluteal muscles. In the biopsy of the hypertrophied gastrocnemius muscle, perivascular inflammatory infiltrates were observed, apart from atrophied and hypertrophied muscle fibres. Electromyography revealed no pathologic spontaneous activity but chronic neurogenic changes. The precise site of the lesion was predicted by electrophysiologic investigations. The lesion was caused by two perineural cysts in the region of the upper sacral plexus, as demonstrated by MRI and CT of the small pelvis and confirmed at operation. Three years earlier, when almost only L5 muscles were affected, an intervertebral disc prolapse L5/S1 had been suspected on myelography and CT but could not have been confirmed at operation.