Isolated extradural sacrococcygeal ependymoma mimicking teratoma in a 5-year-old boy

Introduction

Ependymoma represents the third most common malignant neoplasm of the central nervous system (CNS) in childhood, accounting for about 10% of cases. They predominantly occur in the posterior fossa and supratentorial area, and only 10% are diagnosed in the spinal cord. However, ependymomas account for 22% of all pediatric CNS tumors in the spinal cord (Ostrom et al., Neuro-Oncol 2016; 18 (Suppl 5): v1-v75). Since 1979, ependymomas have been graded according to the WHO classification on morphological criteria and growth pattern as grade III (anaplastic), grade II (classical), and grade I (myxopapillary; MPE) tumors (Gerstner ER et al., Semin Neurol 2018; 38 (1): 104-111). Localization of ependymomas in the sacrococcygeal region, first reported 120 years ago (Mallory FB, J Med Sci 1902; 8 (1): 1-10), occurs very rarely. Most sacrococcygeal ependymomas have been described as pure MPE with predominance in the posterior suprasacral compared to the presacral region, but mixed forms exist. Due to slow growth and nonspecific symptoms, considerably prolonged intervals to diagnosis have been reported. Many cases are initially misinterpreted as pilonidal cysts, followed by chordomas, teratomas, neurogenic tumors, lipomas, hematoma, abscess, or metastases. The clinical course is considered rather indolent with favorable prognosis in most cases although adverse courses have been published in children and in adults. The largest case series on children and adolescents with extraspinal MPE comprises seven patients with limited clinical details (Cimino PJ et al., Pediatr Blood Cancer 2014; 61 (11): 1969-1971). We here describe another child with an unusual ependymoma manifestation.

Case Report

A 5 ½-year-old boy with an otherwise uneventful medical history was transferred for further diagnostic workup of a firm suprasacral soft tissue swelling of 2 cm diameter, which was noticed by his parents incidentally one month before. He presented in excellent condition without any complaints or restrictions. By ultrasound ([Fig. 1a,b]), the well perfused lesion (volume 11 ml) was seen to be located in close proximity to the coccyx. Blood count and clinical chemistry including α-fetoprotein, beta-human chorionic gonadotropin, catecholamine metabolites, and neuron specific enolase were in normal range. Magnetic resonance imaging (MRI) showed a homogeneous tumor (3 ×3 x 2 cm), hyperintense in T2, intermediate in T1 with diffusion restriction, and with moderate contrast medium enhancement ([Fig. 1c,d]). No infiltration of surrounding structures or additional, suspicious lesions were found. Biopsy was performed and revealed a glial tumor with a myxoid matrix, pseudorosettes, and monomorph tumor cells. Immunhistochemically, tumor cells expressed GFAP, S100, and HOXB13. The proliferation rate was at 5%, but focally considerably higher ([Fig. 2a–d]). Based on these findings, the tumor was diagnosed as MPE (CNS WHO grade 2). By global DNA methylome analysis, the tumor belonged to the methylation class of MPE (www.moleculaneuropathology.org, v11b4, score: 0.99) and, more specifically, to the MPE subgroup A (MPE-A), as recently identified in a comprehensive genome profiling study on 185 MPE tumors (Bockmayr M et al., Neuro-Oncol 2022; 24 (10): 1689-1699). Copy number alterations with gains e.g. in chromosomes 4, 5, 7, 9, 11, 13, 16-18, and 20 and losses in chromosomes 2, 8, 10, and 22 were demonstrated ([Fig. 3]). The MGMT promoter was unmethylated. Additional MRI did not show any evidence of craniospinal metastases. The well encapsulated tumor was resected under neuromonitoring, while the coccyx remained. Histology confirmed MPE but with R1 resection. Postoperative MRI was unremarkable and the boy recovered promptly. Due to the molecular adverse MPE-A profile and R1 resection with relevant relapse risk, adjuvant local radiotherapy with protons (54 Gy) has been performed.

Fig. 1 Axial (a) and sagittal (b) ultrasound of the tumor dorsal and caudal of the coccyx. The tumor is of intermediate echogenicity with suggested lobar but homogenous structure and sharply bounded. Axial T2 weighted MRI (Blade fs, c) shows an hyperintense tumor (*) of homogenous texture without infiltration of the surrounding tissue. Coronal T1 weighted fat saturated MRI (vibe dixon, d) demonstrates a moderate, slightly inhomogeneous contrast medium enhancement of the tumor (^).

Fig. 2 H&E staining (a) reveals typical histomorphological features of MPE with perivascular pseudorosettes, papillary growth and a myxoid matrix throughout the tumor. Immunohistochemistry demonstrates strong expression of GFAP in all tumor cells (b), a low to intermediate number of proliferating cells expressing Ki-67 (c), and nuclear expression of HOXB13 as a hallmark of myxopapillary ependymomas (d).

Fig. 3 Copy number profile. Copy number alterations were inferred from global DNA methylation data and show numerous gains and losses throughout the genome.

Publication History

Article published online:
29 March 2023