Case of the Month
Section Editor: Nicholas Stence, MD
Children's Hospital Colorado, Aurora, CO
October 2020
Next Case of the Month Coming November 3...
Medulloblastoma (Group 4) with Radiation-Induced Necrosis (Radionecrosis)
- Background:
- Medulloblastoma is a common posterior fossa tumor of childhood (WHO grade IV) and occurs less commonly in adults.
- It has 4 molecular subgroups as follows:
- Wingless (WNT),
- Sonic hedgehog (SHH),
- Group 3, and
- Group 4.
- Of the 4 subgroups, WNT and SHH are more common in adults, while Group 3 and 4 tumors occur predominantly in children.
- They also differ in terms of enhancement characteristics. WNT tumors tend to show homogeneous enhancement, while Group 3 tumors show heterogeneous enhancement and Group 4 tumors show no enhancement.
- Radiation therapy is used in the treatment of various intracranial tumors, including medulloblastoma.
- There are 3 types of radiation injury:
- Acute (during or shortly after radiation),
- Subacute or early-delayed (up to 12 weeks after radiation), and
- Late (months to years after completion of radiation), which includes radionecrosis, radiation-induced glioblastoma, and radiation-induced meningioma.
- Although radionecrosis is more common within 3 years of radiotherapy, it has been reported to occur up to 19 years posttreatment.
- Differentiating radionecrosis from recurrent or progressive tumor poses a challenge, as both entities present with similar imaging findings and clinical features.
- But their differentiation is important, because if radiation-related changes are mistaken for disease, patients may be subjected to unnecessary surgery and the otherwise effective therapy may be discontinued.
- Clinical Presentation:
- Features of primary tumor will depend on the location; however, usually patients present with features of raised intracranial tension.
- No specific clinical presentation of radionecrosis
- Key Diagnostic Features:
-
Imaging features of medulloblastoma depend on the molecular subgroup.
-
Group 4 tumor, which is our case, is seen as a central posterior fossa tumor with T2 iso- to hyperintensity and no enhancement.
-
Medulloblastoma shows restricted diffusion.
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Radionecrosis is often seen as an enhancing lesion with a central area of necrosis (soap bubble appearance).
-
The solid portion may display a T2 low-to-intermediate signal intensity, while the necrotic portion will show increased T2 signal intensity.
-
The "Swiss cheese" pattern is seen on postcontrast imaging when there are scattered areas of necrosis of various sizes.
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Usually, radionecrosis does not show restricted diffusion, unlike our case.
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No raised choline on MR spectroscopy
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No hyperperfusion on perfusion studies
-
- Differential Diagnoses
- Of posterior fossa tumor in adults:
- Hemangioblastoma: Usually seen as a cystic lesion with mural nodule
- Ependymoma: Tends to be heterogeneous; less likely to show restricted diffusion; extends through the foramina of Luschka and Magendie
- Of radionecrosis: Radiation-induced glioblastoma
- Differentiation from radionecrosis is difficult on conventional imaging. Restricted diffusion is more likely in this entity than radionecrosis. This entity shows hyperperfusion on perfusion studies and raised choline on spectroscopy. Radionecrosis shows low perfusion values and a lipid/lactate peak on spectroscopy.
- Of posterior fossa tumor in adults:
- Treatment:
-
Of medulloblastoma: Surgery, usually with adjuvant radiotherapy or chemotherapy
- Of radionecrosis: Corticosteroids. Biopsy may be considered if steroids do not halt the process or improve symptoms.
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