A picture is worth a thousand... differential diagnosis: lumbar cystic schwannoma

Clinical History

Magnetic Resonance examination was carried out to evaluate a CT incidental finding of a lumbar lesion in a 60 year-old male patient with rectal cancer, during a preinterventional assessment at the Emergency Department.

Imaging Findings

Intraforaminal soft tissue, round in shape, mass with maximum diameter of 20mm at L4 level, widening neural exit foramina with vertebral body scalloping.
Pre-contrast CT: density varies from hypodense to slightly hyperdense (Figure 1).
Post-contrast CT: homogeneous slight contrast enhancement (Figure 2).
Pre-contrast MRI: hypointense in T1-weighted images, hyperintense in T2-weighted images (Figure 3).
Post-contrast MRI: marked peripheral ring-like enhancement with central area of low signal (Figure 4).

Discussion

Nerve sheath tumours are the most common spinal neoplasms accounting for approximate 40% of extramedullary tumours of the spinal column. The majority of these lesions are purely intradural (50-80%) or intradural with extradural extension (10-20%). Purely extradural schwannomas account for 1-10% of all spinal schwannomas and are more often seen in the cervical region. Lumbar extradural schwannomas have accounted for 2.4-3.2% of all nerve sheath tumours and have not often been described in the literature [1]. They are well-described slow growing benign tumours of the peripheral nervous system, arising from Schwann cells. Peak presentation is in the 5th-6th decades. There is no sex predilection.
Presentation depends on location of the tumour. Any cranial nerve may be involved, except CN I and CN II, which lack sheaths composed of Schwann cells. The most commonly involved nerves are: CNVIII (acoustic neuroma), CNV, CNVII, spinal nerve roots and intercostal nerves.
Schwannomas arise eccentrically from their parent nerve. They are composed of two cell types: Antoni A and Antoni B. The Antoni A cells are densely packed and arranged in fascicles. Acellular areas lie between opposing rows of parallel nuclei (Verocay bodies). The Antoni B cells are less compact and are prone to cystic degeneration [2]. It has been described that a schwannoma may display variable degenerative changes such as fibrosis, cytological atypia, calcification, haemorrhage or cystic formations. Various theories have been hypothesized to explain the cystic change occurring in schwannomas. Degeneration of the Antoni B portion of a neuroma can result in cyst formation and may then progress to form a larger cyst [3-5]. Central ischemic necrosis, thrombosis of the vessels with resultant necrosis plus haemorrhage or tumour neovascularity also can be caused by tumour growth, resulting in cyst formation within the tumour[6].
MRI has been considered as the best tool to investigate the spinal cystic schwannomas. Generally, they appear as hypointense on T1-weighted MR images and of various intensity on T2-weighted images, based on the different components within the schwannoma. The hypointensity on T2-weighted images may often correspond to haemorrhage, dense cellularity or collagen deposition, whereas the hyperintensity may represent cystic changes [4]. A contrast study is preferred to differentiate schwannoma from other lesions. Peripheral ring-like enhancement of an extradural extramedullary tumor on MRI should be considered diagnostic of schwannoma, when alternative diagnosis of disk fragment is excluded. Surgical excision was needed when the neurological deficits became progressive. Postoperative histopathological examination of the tissue forms the mainstay of differentiation.

Differential Diagnosis List

Final Diagnosis

Lumbar cystic schwannoma

URL:	https://www.eurorad.org/case/13239
DOI:	10.1594/EURORAD/CASE.13239
ISSN:	1563-4086