Spinal intradural extramedullary cystic (IDEM) schwannoma mimicking myxopapillary ependymoma

A 29-year-old female with complaints of backache with pain radiating to left lower limb since 1 year, gradually increasing in severity. No history of trauma. No history of limb weakness. No bowel / bladder complaints.

MRI of the dorso-lumbar region reveals a well defined intradural extramedullary ovoid lesion in the spinal canal filling the thecal sac. It is seen extending from D11 to D12 vertebral levels. It appears hypointense on T1WI sequence and heterogeneously hyperintense on T2WI sequence. On post-contrast imaging, it shows heterogeneous enhancement of the mass with peripheral rim as well as septal enhancement.

Few foci of blooming are seen on gradient sequences denoting hemorrhagic areas. 

It is seen intradurally, predominantly on the left side with compression and displacement of  the conus medularis, filum terminale and cauda equina towards the right side.

No obvious associated vertebral osseous erosions seen. No extension into neural foramina seen.No paraspinal muscle involvement.

After surgical excision, the histological evaluation characterised the lesion as Schwannoma.

Schwannomas are benign, encapsulated, slow-growing tumours of Schwann cell origin (peripheral nerve sheath) and the most common tumour of peripheral nerves, including cranial nerves. They commonly arise from dorsal sensory roots of cervical and lumbar spine, rarely thoracic. Any cranial nerve may be involved, except CN I and CN II, which lack sheaths composed of Schwann cells. [1]

They are composed of two cell types: Antoni A and B. A cell shows a highly cellular area and Antoni B shows loosely organized myxoid tissue. B cells show predisposition to degenerative changes, such as cyst formation, calcification, haemorrhage. [2]

Peak presentation is in the 5th-6th decades. Clinical presentation varies with the site of lesion, however, most spinal schwannomas typically present with the radiculopathy followed by motor weakness.

MRI is the best modality to investigate the spinal cystic schwannomas. Generally, they appear as hypointense on T1-WI sequences and of various intensity on T2WI sequences, based on the different components within the schwannoma.T2WI hypointensity thus may often correspond to haemorrhage, increased cellularity, whereas the hyperintensity may represent cystic changes.

A cystic schwannoma has a well defined ring-like enhancement of the cyst wall in contrast-enhanced images. However final diagnosis is always histopathological.

Surgical excision is needed when the neurological deficits became progressive.

A definitive understanding of the MRI features of spinal schwannomas, especially the typical enhancement, that is well defined thick walls with septations that show intense enhancement helps in diagnosis. [3]