Posterior vertebral scalloping in a long-standing Schwannoma

Clinical History

The patient presented with aggravating back pain. He had a known spinal lesion at the L4 level, that had been diagnosed as a Schwannoma by CT-guided fine needle aspiration 8 years before. Surgical removal had been refused by the patient.

Imaging Findings

On CT, there was a lesion eroding the borders of the right neuroforamen and especially the dorsal contour of the L4 vertebral body. Its diameter was reduced by half and there was marked rim sclerosis indicating a non-aggressive lesion (Fig. 1). MRI showed a T2-hyperintense, somewhat heterogeneous lesion, that enhanced avidly, but only at the periphery. On native T1 images, the lesion was completely isointense to muscle (Fig. 2).

Discussion

Posterior vertebral scalloping is an exaggeration of the normal concavity of the posterior contour of one or more vertebral bodies. It can be seen on conventional lateral radiographs of the spine and on sagittal and transverse CT or MR images. Scalloping in contrast with osteolysis is characterised by a smooth margin with rim sclerosis towards the spinal canal. It is caused by a mismatch between intra-spinal pressure and bone stability. Systemic disorders, that may lead to vertebral scalloping are connective-tissue diseases, mucopolysaccharidoses, neurofibromatosis type I or ankylosing spondylitis. Occasionally, scalloping may also be caused by local slowly-growing intraspinal masses, such as ependymoma, intra- and extradural spinal cysts, lipoma or Schwannoma [1].
Schwannomas or neurilemmomas are typically benign neoplasms arising from the myelin sheath of spinal nerve roots, cranial or peripheral nerves. In the spine, they may be located intradurally, extradurally or both (dumb-bell type). Most lumbar intradural extramedullary tumours are Schwannomas [2]. Intramedullary location is exceptional [3]. Purely intraosseous Schwannomas of the spine have also been reported, but they represent only less than 0.2% of all primary bone tumours [4]. Due to their slow growth, benign spinal Schwannomas cause little symptoms and may become quite large before they are detected [5]. The most typical radiographic sign is widening of the interpedicular distance, that usually precedes the development of posterior vertebral scalloping in intra-extradural tumours [1]. However, the diagnosis can usually be secured by MRI before bony changes have developed. Characteristic MRI features of Schwannomas besides their anatomic location are hyperintense and heterogeneous signals on T2-weighted as well as contrast-enhanced T1-weighted images [2]. Uncommon presentations may be caused by infarction, cystic degeneration, haemorrhage or melanin content of these neoplasms [6].

Differential Diagnosis List

Final Diagnosis

Schwannoma (Neurilemmoma)

URL:	https://www.eurorad.org/case/9312
DOI:	10.1594/EURORAD/CASE.9312
ISSN:	1563-4086