Imaging in sacrococcygeal subcutaneous myxopapillary ependymoma: Sporadically reported from Asian population

INTRODUCTION

Ependymomas outside the spine are uncommon, with most of them being subcutaneous in the sacrococcygeal region. It is uncommonly reported from Asian population, however no race variation is noted.

CASE REPORT

A 11-year-old boy presented at surgical outpatient department with complain of natal cleft swelling with discomfort. Clinical examination revealed a non-tender mobile subcutaneous swelling of approximate size (4 × 8) cm with no apparent abnormality of the overlying skin [Figure 1]. As part of further evaluation local part, ultrasound examination was performed. A well-defined heterogeneously hypoechoic lesion with significant internal vascularity was found [Figure 2]. Pelvic and lumbo-sacro-coccygeal magnetic resonance imaging (MRI) examination was done for lesion characterization and delineation of its extent. MRI examination demonstrated a well-defined, well-circumscribed subcutaneous intermediate T2 and high short tau inversion recovery signal intensity lesion of size (4.8 × 2.9 × 6.5) cm (AP × TRA × CC) with multiple internal hypointense septae, and well-defined hypointense septae capsule in sacrococcygeal region at upper edge of intergluteal cleft. Lesion showed minimal diffusion restriction on diffusion-weighted imaging (with minimal low signal on corresponding apparent diffusion coefficient maps). Intense enhancement on post-contrast T1-weighted MRI with non-enhancing internal fibrous septae and peripheral fibrous capsule was evident [Figure 3]. The lower dural sac, cauda equina, and cone were found to be unremarkable. Radiologically, subcutaneous myxopapillary ependymoma was diagnosed based on MRI features and was confirmed histologically [Figure 4].

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Figure 1:

Clinical examination image showing swelling in intergluteal cleft region.

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Figure 2:

(a) Sagittal gray scale ultrasound image showing well-defined heterogeneously hypoechoic lesion subcutaneously in sacrococcygeal region at upper edge of intergluteal cleft (b) lesion demonstrated internal vascularity on color Doppler ultrasound.

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Figure 3:

Magnetic resonance images (a-f): Lesion in subcutaneous plane in sacrococcygeal region at upper edge of intergluteal cleft shows intermediate signal on (a) T2W sagittal image, (b) high signal on short tau inversion recovery axial image, with hypointense capsule and septa. Minimal diffusion restriction with low signal on corresponding apparent diffusion coefficient maps (c and d) and intense enhancement with non-enhancing capsule and septa on T1W post-contrast images (e) sagittal and (f) coronal.

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Figure 4:

Histology images (a and b) H and E-stained sections show tumor tissue arranged in papillary pattern, Papillae show central fibrovascular core, at places stroma show bluish myxoid like areas. Papillae are lined by cells having round nuclei with elongated cytoplasm. No evidence of mitosis, necrosis or microvascular proliferation is seen. Overall findings suggest histology of myxopapillary ependymoma. H and E: Hematoxylin and eosin.

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DISCUSSION

The rare occurrence of ependymoma outside the spine is probably due to heterotopic sites having the ependymal cells. Four general scenarios exist for the ependymomas outside the spine. (i) As metastasis from a primary central nervous system (CNS) ependymoma, (ii) primary spinal cord, cauda equina, or filum terminale ependymoma extending directly into the sacrococcygeal soft tissues, (iii) primary cutaneous and subcutaneous neoplasm without spinal cord communication, and (iv) primary tumor of abdominal, pelvic, or presacral region.^[1,2] The third scenario holds true in our case. Myxopapillary ependymomas are now classified as the World Health Organization Grade II CNS neoplasms instead of Grade I because the prognosis is now similar to traditional ependymomas.^[3] The myxopapillary variant of ependymoma is an extremely rare type of ependymoma. These well-circumscribed tumors with slow growth rate can occur at any age mainly in young adults with the mean age of diagnosis being 36 years.^[4] Ependymomas outside the spine in the sacrum are presacral or retro sacral masses. The most likely extraneural pathways for ependymal tumors are likely to be the lymphatic or hematogenous spread.^[5] A presacral mass can cause mass effect on the bladder or bowel, and a post-sacral mass can present as swelling of the buttocks.^[6] The diagnostic technique of choice for the diagnosis, grading, and staging of these tumors is MRI. The management of the ependymoma is determined according to the grading and the tumor site. Metastases were more frequent in very rare extrathecal post sacral (18%) than in presacral ependymomas (7%). Pulmonary, skeletal, and regional nodal and hepatic metastasis occurs in sacrococcygeal myxomapillary ependymoma.^[5] Complete surgical removal is the key to curative treatment. Metastatic disease, incomplete removal, and coccygeal involvement require coccygectomy and post-surgical radiotherapy.^[7,8] Due to risk of metastasis and local recurrence, long duration close follow-up is required. Complete removal at the initial operation provides the best survival outcome in patients with these tumors.^[9] We report a case of a subcutaneous sacrococcygeal myxopapillary ependymoma in a young boy. As far as we know, rare previous sporadic reports have been there in Asian patients.

DIFFERENTIAL DIAGNOSES

Pilonidal disease

Sacrococcygeal teratoma

Lipoma

Neurogenic tumor

Soft tissue sarcoma

Metastases

CONCLUSION

Subcutaneous myxopapillary ependymoma in sacrococcygeal region is extremely rare tumor with a tendency to affect children and adolescents. MRI is the imaging modality of choice for the detection, grading, and staging of this condition. Important treatment consideration is complete surgical excision at the initial operation. Long-term and close follow-up is required because this tumor may recur locally or become metastatic.

TEACHING POINTS

1. Although subcutaneous myxopapillary ependymoma is extremely rare entity but based on its sacrococcygeal location and characteristics seen on MRI, it should be considered as an important differential diagnosis and evaluated further.

2. Long-term post-operative, follow-up is suggested for evaluation of metastases.

MCQs

1. Which of the followings characterize subcutaneous myxopapillary ependymoma?

   1. World Health Organization grade II tumor

   2. Tends to affect children and adolescents

   3. Complete surgical excision is recommended treatment approach

   4. All the above

   Answer Key: d

2. MRI findings in case of myxopapillary ependymoma include:

   1. Intermediate/high T2 signal intensity lesion

   2. Intense post-contrast enhancement

   3. Well-defined non-enhancing fibrous capsule with multiple internal non-enhancing fibrous septae

   4. All the above

   Answer Key: d

3. Which of the following is true regarding myxopapillary ependymoma?

   1. Slow growing tumor

   2. No recurrence

   3. No distal spread

   4. Very high incidence

   Answer Key: a