Atypical giant sacral myxopapillary ependymoma with massive osteolysis

Clinical History

29-year-old nulliparous woman with six-month history of sacrococcygeal pain radiating to the right thigh and leg and two-week history of rectal tenesmus and urinary retention. Paravertebral spasm and reduction of several reflexes were noted. Laboratory investigations were normal. Rectal examination revealed a rectum reduced in lumen by extrinsic compression posteriorly.

Imaging Findings

MRI showed a large mass arising from the sacrum, extending into the presacral space (Fig. 1). The mass was hypo-isointense on T1 images (Fig. 2), hyperintense on T2 (Fig. 3a, 3b), marked hyperintense on DWI and hypointense on the corresponding ADC map (Fig. 4a, 4b). After administration of gadolinium, the mass showed little homogeneous enhancement (Fig 5). MRI of the spine above the sacral region did not reveal any abnormality. The lesion seemed to originate from the L5-S1 nerve root sheaths (Fig. 6), which were dislocated laterally without signs of infiltration.
Whole body CT scan revealed marked sacral erosion (Fig. 7), the lesion was isodense compared with the spinal cord and did not enhance after administration of contrast material. There was no evidence of metastases.
The patient was treated with an en bloc sacral resection. A histological diagnosis of myxopapillary ependymoma was made.

Discussion

Myxopapillary ependymomas (MPE) frequently occur in the sacrum during the 40s and may cause bone destruction [1, 2].
On CT, MPE are iso-hyperattenuated compared to the spinal cord. They have calcifications and show enhancement, although in our case these two features were not observed.
On MRI, MPE present T2 iso-hyperintensity, T1 iso-hypointensity and may have haemorrhagic or cystic areas, although not detected in our case. They present enhancement after gadolinium injection [3].
The predilection for the conus medullaris is suggestive of the diagnosis but there are other sacral tumours with bone destruction, such as chordoma, giant cell tumour, chondrosarcoma, aneurysmal bone cyst, plasmacytoma and metastases. On DWI most of sacral solid neoplasms show restricted diffusion; however, the diagnostic value of DWI may be limited in the differential diagnosis [1].
Chordoma have calcifications, and MRI findings may be similar to MPE. However, MPE arise in the spinal canal rather than bone, and they usually present more enhancement than chordomas [1].
Giant cell tumours are bone tumours with no calcifications. T1 and T2 hypointensity, due to presence of fibrosis, may distinguish them from MPE [4].
Chondrosarcomas are osteolytic lesions with ring-and-arc calcifications on CT and heterogeneous signal intensity on T1 and T2 MRI images. They do not present haemorrhage; this helps differentiate them from MPE [5].
Metastases present T2 hyperintensity and strong enhancement. Metastases raise diagnostic problems when they are isolated; however, usually the primary cancer is already known [6].
Aneurysmal bone cysts are rare in the sacrum and present blood-filled cystic areas. The diagnosis is suggested by a regular cortical rim on CT and the absence of a solid tissue component [6].
Plasmacytomas occur in the elderly, are usually eccentric, hypointense on T2 MR images and present as osteolytic lesions although overall sacral structure is usually preserved [6].
Sacral schwannomas usually grow along nerve segments and expand the neural foramina; MRI findings may be similar to MPE but they usually present only minor bone involvement [7].
The frequent presence of haemorrhage and calcifications, the predominantly solid appearance, the strong gadolinium-based contrast enhancement, hypointensity on T1, hyperintensity on T2 and its origin from the spinal canal rather than bone are the most important findings to make a diagnosis of MPE [8]. However, in our case, the absence of cysts, haemorrhage, calcifications and of the typical intense CT enhancement raised diagnostic problems.
However usually both CT and MRI may help limit differential diagnosis in cases of sacral lesions and guide surgery.

Differential Diagnosis List

Final Diagnosis

Sacral myxopapillary ependymoma

URL:	https://www.eurorad.org/case/13332
DOI:	10.1594/EURORAD/CASE.13332
ISSN:	1563-4086