CNS tumor with BCOR internal tandem duplication

Last revised by Richard Gagen on 10 Mar 2023

CNS tumor with BCOR internal tandem duplication (BCOR-ITD) is a rare and relatively new brain tumor type that has been added to the WHO classification of CNS tumors 5th edition as part of the embryonal family of tumors. Originally identified through molecular analysis of tumors classified as primitive neuroectodermal tumors of the CNS 1, they share similar clinical and imaging characteristics and are primarily an intra-axial tumor of young children occurring in the cerebral and cerebellar hemispheres 2. As yet only a small numbers of cases that include imaging findings have been reported in the literature 3.

Tumors showing BCOR-ITD are more common in males (male to female ratio of 1.5) with an average age at diagnosis of 4.5 years 4. While the majority of cases occur in children, some cases in young adults have been reported 5.

Genetically related tumors with BCOR fusion (rather than the tandem duplication) appear to occur with a more even gender distribution and with an older age at presentation 4.

Clinical symptoms are those of an intracranial mass lesion and include headaches alongside other symptoms of raised intracranial pressure, seizures and focal neurologic deficits 2,3.

The causative recurrent internal tandem duplication occurs within exon 15 of the BCOR transcriptional co‐repressor gene 1. Somatic alterations in BCOR are associated with a variety of tumor types, with internal tandem duplications thought to be the driving mutation behind clear cell sarcomas of the kidney and the sarcoma with BCOR genetic alteration 2.

CNS tumors showing BCOR-ITD are typically densely cellular and well-circumscribed from the normal brain parenchyma 2,3,5, though occasionally showing infiltration at their interface with the surrounding brain 2. Tumor cells have round to oval nuclei. Ependymoma-like perivascular pseudorosettes, palisading necrosis and a dense capillary network without microvascular proliferation have been described as features 2,5.

  • BCOR: strong and diffuse positive expression 5

  • OLIG2: positive in most tumors with variable labeling of cells 2,5

  • GFAP: majority of tumor cells negative 2,5

  • NeuN: positive in most tumors with variable labeling of cells 2

  • synaptophysin (Syn): negative 2,5

  • epithelial membrane antigen (EMA): negative 2,5

Currently, only a few short case series have been published describing imaging findings in CNS tumors with BCOR-ITD. As such it is likely the imaging findings associated with this tumor type will evolve with further publications.

A case series of 10 patients published by Cardoen et al 3 described peripheral well-defined intra-axial masses occurring in both the cerebral and cerebellar hemispheres. The tumors were large at presentation and commonly abutted the dura without invasion. Areas of central necrosis were common, with some of the masses showing calcifications or areas of hemorrhagic change. The masses demonstrated minimal to no surrounding vasogenic edema and only mild heterogenous enhancement. In 9 of 10 cases, large vessels draining to overlying cortical veins were seen within the tumor. Similar imaging findings were described in a case series of 10 additional patients published by Ferris et al 2.

Approximately 8% show CNS dissemination at the time of diagnosis 4.

  • T1: hypointense to grey matter

  • T2/FLAIR: slightly hyperintense to grey matter

  • T1 C+ (Gd): mild heterogenous enhancement

  • DWI/ADC: reduced diffusivity, with similar ADC values to that of cortex.

  • perfusion: relatively low cerebral blood flow (CBF) values compared to normal parenchyma

Treatment consists of gross total resection where possible and a regimen of chemotherapy with or without radiotherapy 2.

  • embryonal tumor with multilayered rosettes

    • similar imaging features, including intra-tumoral veins, restricted diffusion, minimal or absent edema and frequent calcifications

    • do not demonstrate frequent central necrosis

  • atypical teratoid / rhabdoid tumor (AT/RT)

    • more commonly show peripheral cystic components, mild surrounding edema and more marked enhancement of solid components

    • CNS dissemination is common at the time of diagnosis

  • medulloblastoma

    • SSH subtype are typically peripherally located but show a more diffuse nodular pattern of growth

    • group 3 and 4 subtypes typically arise from the vermis

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