DIAGNOSIS Traumatic Neuroma
Common lesions in the differential diagnosis for extramedullary, intraparenchymal masses at the lumbosacral level include schwannoma, ependymal neoplasms, paraganglioma and meningioma. Less common entities to be considered include metastasis, hemangioblastoma, neurofibroma, perineurioma, and traumatic neuroma. Microscopically, this lesion is composed of interlacing bundles of myelinated axons, ruling out non-peripheral nerve lesions. The presence of abundant axons with thin myelin sheaths and absence of hypertrophic/onion bulb features rule out schwannoma, neurofibroma and perineurioma. Based on the histology, location and history of hemipelvectomy the diagnosis is traumatic neuroma. Traumatic neuroma is a non-neoplastic, disorganized proliferation of axons with accompanying Schwann and perineurial cells set in a collagenous stroma, occurring at the site of partial or complete nerve transection (1). When the nerve is transected and if the severed ends are in close approximation, the regenerating and sprouting axons can traverse the narrow gap and reestablish the continuity of the nerve. However, when the gap is wide or filled with inflammatory cells or collagenous scar, the attempt at regeneration is unsuccessful and results in a mass known as traumatic neuroma. Unlike most distally located traumatic neuromas seen in general surgical pathology, in this case, the relative paucity of connective tissue elements in spinal nerve rootlets has eliminated the typical scarred background.
Traumatic neuromas may also arise as a post-surgical complication involving somatic and/or visceral nerves (1,2). Examples include amputation neuromas and those following visceral surgeries such as cholecystectomy. They present as firm, slow growing and often painful masses at the site of injury. Grossly they are firm, demarcated, fusiform to bulbous masses arising at the proximal stump, measuring 1-2 cm and rarely approaching 5 cm (1). Microscopically, the hallmark of traumatic neuroma is a haphazard arrangement of regenerating axons in a background of Schwann cells, perineurial cells and connective tissue elements. Compared to an intact nerve, the myelination of axons is generally scant. Formation of a traumatic neuroma is usually prevented by close approximation of the nerve at the time of surgery to promote reinnervation. Placement of a nerve graft across the site of injury may also facilitate regeneration. Resection of the neuroma is curative of pain. In this case, review of the patient's medical record has not revealed a history of pain related to the distribution of left lumbar nerve rootlets.
Contributed by Andrew R. Virata; Padmini V. Holla; M. Shahriar Salamat