A Case of Desmoplastic Medulloblastoma Initially Misdiagnosed as Lymphoma in a 54-year Female Patient

By Ahmet Mesrur Halefoglu¹, Canan Tanik²

Affiliations

1. Department of Radiology, Sisli Hamidiye Etfal Training and Research Hospital, Istanbul, Turkiye
2. Department of Pathology, Sisli Hamidiye Etfal Training and Research Hospital, Istanbul, Turkiye

doi: 10.29271/jcpsp.2026.08.1101

Sir,

Medulloblastoma (MB) is a highly aggressive and invasive embryonal tumour that occurs in the cerebellum.¹ They are classified as the World Health Organization (WHO) grade 4 tumours and were historically grouped within the primitive neuroectodermal tumour (PNET) family.² MBs are among the most common malignant brain tumours in children; however, they are rarely encountered in adults, accounting for less than 1% of all central nervous system (CNS) neoplasms.³

A 54-year female was admitted to the hospital with complaints of severe headache, intermittent vertigo, and imbalance over the preceding week. On non-contrast computed tomography (CT), a hyperdense, intra-axial mass lesion measuring 41 x 37 mm was identified in the right cerebellar hemisphere (Figure 1A). For further evaluation, magnetic resonance imaging (MRI) was performed, revealing a right cerebellar hemispheric intra-axial mass measuring 45 x 42 x 32 mm. The lesion demonstrated a hypointense signal on T1-weighted and T2-weighted images. Following intravenous gadolinium DTPA administration, the mass exhibited strong, solid contrast enhancement (Figure 1B).

Diffusion-weighted imaging (DWI) showed marked restrictive diffusion within the lesion with corresponding hypointensity on the apparent diffusion coefficient (ADC) map (Figure 1C and D). Based on these imaging findings, primary CNS lymphoma was initially considered in the differential diagnosis. A comprehensive systemic workup with PET-CT to exclude metastatic disease was negative. The patient subsequently underwent a right-sided suboccipital craniotomy with gross total resection of the cerebellar mass. Postoperative imaging demonstrated no residual pathological contrast enhancement consistent with complete tumour resection (Figure 1E). Histopathological examination revealed a WHO grade 4 medulloblastoma, with extensive nodular architecture, an uncommon histological subtype in this age group. Immunohistochemical analysis was performed to determine the molecular subtype, which was classified as an Sonic Hedgehog (SHH)-activated, TP53-wildtype medulloblastoma (Figure 2A and B).

Adult MB is an extremely rare entity, accounting for approximately 0.4%-1% of all adult brain tumours, with an annual incidence of 0.6 cases per million individuals.⁴ In the imaging evaluation of MB, CT is often used as the initial modality to detect or confirm the presence of a tumour. In routine MRI protocols, DWI is strongly recommended because of the hypercellular nature of  MBs,  which  typically  results  in  restricted  diffusion.

Figure 1 (A,B,C,D,E): (A) Axial non-contrast CT scan shows a hyperdense, intra-axial mass lesion located in the right lateral cerebellum. (B) Axial gradient-echo T1-weighted contrast-enhanced image, showing strong and solid enhancement of the mass with surrounding oedema. (C) Axial DWI reveals marked hyperintensity in the mass lesion. (D) Axial ADC map, obvious hypointensity is seen, indicating a severe restrictive diffusion. (E) Axial post-operative CT scan shows post-operative changes, including haemorrhage within the tumour bed without evidence of residual mass lesion.

According to the 2021 WHO classification of CNS tumours, MBs are categorised into four main histological patterns: classic, extensive nodularity, desmoplastic/nodular, and large cell/ anaplastic. On a molecular level, they are further classified into four distinct subgroups:  SHH-activated, TP53-wildtype; wingless-type (WNT)-activated; SHH-activated, TP53- mutant; and non-WNT/non-SHH.⁵ As surgery alone is associated with a high recurrence rate, adjuvant therapy is needed. Radiotherapy is beneficial in adult MB patients and should be initiated within 90 days following surgery. In high-risk patient groups, additional chemotherapy is recommended.

Figure 2 (A,B): (A) Haematoxylin and eosin (H&E)-stained section show-ing malignant tumour infiltration composed of small, round cells form-ing Hommer-Wright rosettes in a diffuse distribution within the fibrovascular stroma ( H&E, × 200). (B) Immunohistochemical staining demonstrating diffuse cytoplasmic positivity for synaptophysin (synaptophysin, x 200).

In conclusion, this case highlights that although rare, MB should be included in the differential diagnosis of posterior fossa tumours in older patients presenting with characteristic imaging findings.

COMPETING  INTEREST:
The  authors  declared  no  conflict  of  interest.

AUTHORS’  CONTRIBUTIONS:
AMH: Designed the study, analysed the data, drafted the manuscript, and supervised the study.
CT:  Revised  the  manuscript  critically.
Both  authors  approved  the  final  version  of  the  manuscript  to  be  published.

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