Answer for BIR CoW 21 Mar 2021
ATYPICAL RHABDOID TERATOID TUMOR
Findings
Well defined lobulated T1 hypointense and T2 heterointense lesion measuring 5.4x4.2x3.5 cm with patchy areas of intra tumoral hemorrhage noted with significant perilesional edema causing mass effect over the lateral ventricles and transfalcine herniation to the left side. The lesion shows areas of low ADC values with peritumoral cysts in the medial parasagittal region. On contrast administration the lesion shows heterogenous enhancement with areas of necrotic components.
Discussion
Atypical teratoid/rhabdoid tumours (AT/RT) are an uncommon WHO grade IV tumour, which in the vast majority of cases occurs in young children less than two years of age. It most frequently presents as a posterior fossa mass. AT/RT often resembles medulloblastoma by imaging and even H&E microscopy, and the diagnosis requires cytogenetic analysis of the tissue.
Epidemiology They present in young children (median age is less than 2-3 years ), whereas medulloblastomas typically occur in mid-childhood (median age 6 years). Pathology Microscopic features Rhabdoid cells are the hallmark of AT/RT, but only comprise a fraction of the tumour. Other portions of the tumour are indistinguishable on imaging and histology from a medulloblastoma or embryonal tumour with multilayered rosettes. According to 2016 WHO classification scheme, a diagnosis of AT/RT requires confirmation of specific genetic aberration (loss of INI1 tumour suppressor gene on chromosome 22 or BRG1 gene); otherwise, a descriptive diagnosis of CNS embryonal tumour with rhabdoid features is used. Immunophenotype • EMA: positive • vimentin: positive • smooth muscle actin: positive Radiographic features Atypical teratoid/rhabdoid tumours are usually large and very heterogeneous masses. They may be difficult to distinguish from a PNET by imaging. Location • infratentorial: ~50% o cerebellum (most common) o brainstem • supratentorial o cerebral hemispheres o pineal gland region (see pineal mass differential diagnosis) o septum pellucidum o hypothalamus CT • often isodense to grey matter • may demonstrate heterogeneous enhancement • calcification is common • may show associated obstructive hydrocephalus MRI Can show necrosis, multiple foci of cyst formation and sometimes hemorrhage: • T1: iso- to slightly hyperintense to grey matter (haemorrhagic areas can be more hyperintense) • T2: generally hyperintense (haemorrhagic areas can be hypointense) • T1 C+ (Gd): heterogeneous enhancement • MR spectroscopy o Cho: elevated o NAA: decreased • DWI o almost all restrict diffusion Leptomeningeal seeding has been described in up to 15-30% of cases and so post-contrast imaging of the entire neuroaxis should be considered in suspected AT/RTs. Differential diagnosis • supratentorial CNS PNET • medulloblastoma • intracranial teratoma
Findings
Well defined lobulated T1 hypointense and T2 heterointense lesion measuring 5.4x4.2x3.5 cm with patchy areas of intra tumoral hemorrhage noted with significant perilesional edema causing mass effect over the lateral ventricles and transfalcine herniation to the left side. The lesion shows areas of low ADC values with peritumoral cysts in the medial parasagittal region. On contrast administration the lesion shows heterogenous enhancement with areas of necrotic components.
Discussion
Atypical teratoid/rhabdoid tumours (AT/RT) are an uncommon WHO grade IV tumour, which in the vast majority of cases occurs in young children less than two years of age. It most frequently presents as a posterior fossa mass. AT/RT often resembles medulloblastoma by imaging and even H&E microscopy, and the diagnosis requires cytogenetic analysis of the tissue.
Epidemiology They present in young children (median age is less than 2-3 years ), whereas medulloblastomas typically occur in mid-childhood (median age 6 years). Pathology Microscopic features Rhabdoid cells are the hallmark of AT/RT, but only comprise a fraction of the tumour. Other portions of the tumour are indistinguishable on imaging and histology from a medulloblastoma or embryonal tumour with multilayered rosettes. According to 2016 WHO classification scheme, a diagnosis of AT/RT requires confirmation of specific genetic aberration (loss of INI1 tumour suppressor gene on chromosome 22 or BRG1 gene); otherwise, a descriptive diagnosis of CNS embryonal tumour with rhabdoid features is used. Immunophenotype • EMA: positive • vimentin: positive • smooth muscle actin: positive Radiographic features Atypical teratoid/rhabdoid tumours are usually large and very heterogeneous masses. They may be difficult to distinguish from a PNET by imaging. Location • infratentorial: ~50% o cerebellum (most common) o brainstem • supratentorial o cerebral hemispheres o pineal gland region (see pineal mass differential diagnosis) o septum pellucidum o hypothalamus CT • often isodense to grey matter • may demonstrate heterogeneous enhancement • calcification is common • may show associated obstructive hydrocephalus MRI Can show necrosis, multiple foci of cyst formation and sometimes hemorrhage: • T1: iso- to slightly hyperintense to grey matter (haemorrhagic areas can be more hyperintense) • T2: generally hyperintense (haemorrhagic areas can be hypointense) • T1 C+ (Gd): heterogeneous enhancement • MR spectroscopy o Cho: elevated o NAA: decreased • DWI o almost all restrict diffusion Leptomeningeal seeding has been described in up to 15-30% of cases and so post-contrast imaging of the entire neuroaxis should be considered in suspected AT/RTs. Differential diagnosis • supratentorial CNS PNET • medulloblastoma • intracranial teratoma
Note:
We do not discourage differential diagnosis. But all the differentials must satisfy the findings noted in the case.
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Did you Know?
The order in which the names appear in this winner's list is based on the time of submission. The first person to send the correct answer gets his/her name on top of the list!
We do not discourage differential diagnosis. But all the differentials must satisfy the findings noted in the case.
If you feel you have answered rightly but cannot find your name in the above list, please call 09551942599.
Did you Know?
The order in which the names appear in this winner's list is based on the time of submission. The first person to send the correct answer gets his/her name on top of the list!