Paediatric medulloblastoma: Atypical CT features at presentation in the SIOP II trial

Abstract

A review of cranial CT studies of 233 patients for the Second Medulloblastoma Trial of the International Society of Paediatric Oncology showed "typical" CT appearances in only 30% of patients. The varied appearances encountered are described with particular emphasis on atypical CT features.

Neuroimaging of pediatric posterior fossa tumors including review of the literature

“…Because of their high cellularity, tumor cells with scant cytoplasm and dense, hyperchromatic nuclei, MBs are almost always hyperdense or isodense compared to the surrounding tissue. A peritumoral vasogenic edema is reported in 90–95% of patients and is mostly mild to moderate (19). Following contrast administration, most MBs enhance diffusely and homogeneously, but patchy enhancement has been reported (20).…”

“…Contrast enhancement is usually present, but may be variable in degree, ranging from diffuse and homogeneous to focal and patchy (24). Lack of enhancement is uncommon and is reported in approximately 7.5% of the tumors (19). Leptomeningeal enhancement mimicking meningioma can be found in eccentric hemispheric MBs of the desmoplastic type because of a desmoplastic reaction of the overlying meninges (20).…”

Neoplasms of the Posterior Fossa

“…Iso-to hypointensity compared to white matter on T1-weighted images and variable signal intensity compared to white matter on T2-weighted images is typical [31]. Virtually all (97%) show at least some enhancement on post-contrast imaging studies [27] (Fig. 2).…”

“…Most (89-95%) of all medulloblastomas demonstrate at least some hyperattenuation compared to normal cerebellar attenuation on nonenhanced CT and have marginal vasogenic edema [13,25,27] Heterogeneity, with cyst formation (59%) and calcification (22%), are commonly [27]. Atypical features include ill-defined margins, absence of vasogenic edema or hydrocephalus, hypoattenuation, hemorrhage, absence of enhancement on post-contrast images, and the appearance of "primary" leptomeningeal dissemination [13,25,[27][28][29]. The presence of falcine calcification in children with medulloblastoma may be a marker for nevoid basal cell carcinoma [30].…”

“…Post-operative evaluation of such spread is hampered by the presence of hemorrhage within the cerebrospinal fluid (CSF) and may lead to false-positive results in the first 2 post-operative weeks, either from the presence of methemoglobin or from leptomeningeal irritation caused by subarachnoid blood [34] Corroboration with clinical and cytopathologic CSF findings is crucial to substantiate the diagnosis of CSF dissemination [35]. In contrast to ependymoma and choroid plexus tumors, foraminal extension by a medulloblastoma from the fourth ventricle to involve the cerebellopontine angle (CPA), cisterna magna, and other cisternal compartments is not common [27,36].…”