Laboratory Studies
Lab tests are not helpful in the diagnosis of embryonal tumors affecting the CNS.
Imaging Studies
Diagnosis of embryonal tumors of the CNS is confirmed or excluded by CT scan and, more importantly, MRI. For the possible diagnosis of leptomeningeal spread, obtaining an MRI of the entire CNS early on in the diagnosis process and a lumbar puncture that will allow sending the CSF for cytology is essential. In case of a large brain mass, it is advisable to avoid early lumbar puncture before surgical resection to minimize the risk of possible herniation.
Clinical diagnosis of these tumors is not possible. Radiologic features unique to each type of tumor may be helpful, but the only possible absolute confirmation is by pathologic examination of the surgical specimen.
Magnetic resonance imaging
Non-medullobllastoma embryonal tumors are usually diagnosed when they have reached a considerable size. This is partly because of the early age at which these tumors are usually diagnosed (in children younger than 2–3 years old). In some patients, the anterior fontanelle is still open, which allows for some pressure release, which can lead to a sizeable growth of the tumor before symptoms start. This is usually the case for large hemispheric cerebral tumors; however, for posterior fossa tumors, the presentation can be much more acute because of obstructive hydrocephalus. The tumor appears large, nicely delineated from the surrounding brain, as a solid mass featuring patchy or no contrast enhancement. Surrounding edema is common, with significant mass effects and possible radiographic herniation signs. Some tumors can show cystic components and microcalcifications.
MRI sequences:
- T1: decreased intensity
- T2: increased intensity
- T1 with contrast (gadullinium): patchy or no contrast enhancement
- DWI: usually, some areas will have diffusion-restricted areas and dark on ADC
- Spectroscopy shows features suggesting hypercellularity (a choline peak and a high ratio of choline/aspartate).
Large supratentorial mass on a toddler. This tumor pathology was of non-medulloblastoma embryonal tumor with final diagnosis of ETMR. On this image, axial T2 with slight hyper intensity
Typical findings include moderate tointense enhancement of the tumor, which is not homogenous (see image below).
DWI sequence shows restricted diffusion. Matched ADC map (not shown) correlated with dark signal
T1 with contrast of large right frontal tumor, shows very slight patchy enhancement (ETMR)
In case there is a posterior fossa mass, accompanying hydrocephalus is common (see image below), and associated cystic changes can occur (see image below).
Cerebellar medulloblastoma. This sagittal view MRI without contrast demonstrates characteristic midline cerebellar location with mild obstructive hydrocephalus.
The entire neuraxis should be imaged to detect spinal metastases, which may occur via subarachnoid dissemination.
CT scan
In emergent situations, a CT scan is preferred over MRI because of its easy accessibility. However, CT scan resolution is inferior to that of MRI. CT myelogram may rule out spinal dissemination in cases in which MRI is contraindicated. It is important to mention that most of the emergencies related to large embryonal tumors are secondary to either large mass effect or obstructive hydrocephalus. In most cases, measures for alleviation of mass effect, such as steroids, will help to allow MRI scan prior for intervention. For obstructive hydrocephalus, measures for either permanent (shunt, ETV) or temporary (EVD) solutions can be used to allow a more through preoperative workup, including MRI.
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Cerebellar medulloblastoma. This MRI (axial view, T2-weighted image) demonstrates the heterogeneity of the tumor.
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Cerebellar medulloblastoma. This sagittal view MRI without contrast demonstrates characteristic midline cerebellar location with mild obstructive hydrocephalus.
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Cerebellar medulloblastoma. This axial view CT scan with contrast shows a partially enhancing mass arising in the midline from cerebellum and filling the fourth ventricle.
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Large supratentorial mass on a toddler. This tumor pathology was of non-medulloblastoma embryonal tumor with final diagnosis of ETMR. On this image, axial T2 with slight hyper intensity
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DWI sequence shows restricted diffusion. Matched ADC map (not shown) correlated with dark signal
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T1 with contrast of large right frontal tumor, shows very slight patchy enhancement (ETMR)
