Extra spinal ependymoma at level of coccyx, subcutaneous type

Findings

A well-defined low density mass which is adherent to the coccyx bone and extends posteriorly to the skin. No rectal invasion. No bony destruction.

Differential diagnosis
- Sacrococcygeal teratoma.
- Lipoma.
- Pilonidal cyst.
- Extraspinal ependymoma
- Coccygeal chordoma
- Rhabdomyosarcoma


Diagnosis: Extra spinal ependymoma at level of coccyx, subcutaneous type


Discussion

Ependymomas are the most common tumors of glial origin in the spinal cord and are usually located in the cauda equina or filum terminale. Extra spinal medullary ependymomas are rare. There are two types, the subcutaneous type and the presacral type. The subcutaneous type can occur due to residual ependymal tissue present at the coccygeal medullary vestige, which is a remnant of the caudal portion of the neural tube. This ependymal-lined structure is present at the post-anal pit, in the subcutaneous soft tissues over the end of the coccyx. This patient has a subcutaneous type. The presacral type is thought to arise from extradural remnants of the filum terminale or as an extension of intradural filum terminale.

This patient had the myxopapillary type of tumor, which is the most common subcutaneous type of extra spinal ependymoma. Papillary and subependymal types also exist. Immunohistochemical stains can aid in the diagnosis with positive stains for glial fibrillary acidic protein, S-100 and vimentin.

These tumors are slow-growing and tend to present late, with a mean age of 17 years of age. There is equal male and female distribution. The mass is usually asymptomatic, located at the intergluteal fold. These masses are frequently misdiagnosed as a pilonidal cyst.

Surgical resection is curative. The survival rate is 85-100%. Metastases occur in about 20%, including pulmonary, pleural, osseous, and inguinal nodal metastases have been documented. Distant metastases can occur up to 10-20 years after the initial presentation. For presacral ependymomas, local recurrence occurs in 71% if the coccyx is not excised. Radiotherapy is recommended for incomplete resection or local metastases. Chemotherapy is not currently recommended.