Brain tumors in children

Imaging protocols and follow-up

The diagnosis of pediatric brain tumors requires mandatory contrast-enhanced MRI of the brain and entire spinal cord. The standard protocol includes acquiring images in various sequences: axial T2-weighted imaging (T2WI), coronal FLAIR, spin-echo (SE) T1WI in three planes before and after contrast administration, as well as diffusion-weighted imaging (DWI) or diffusion tensor imaging (DTI).

The timing of spinal cord MRI is of particular importance—it should be performed prior to surgical intervention. This is necessary to rule out false-positive results caused by blood pooling and artifacts. In emergency cases, the scan is postponed to the postoperative period, but with mandatory T1WI acquisition before and after contrast administration.

Follow-up scanning after tumor resection must be performed within the first 24 hours. Later imaging may show nodular contrast enhancement mimicking residual tumor (linear enhancement within the first 24 hours requires cautious evaluation).

Posterior fossa tumors

The most common intra-axial posterior fossa tumors are medulloblastoma and pilocytic astrocytoma. Ependymomas and atypical teratoid/rhabdoid tumors (ATRT) are less common. Hemangioblastomas are rare in children and are frequently associated with von Hippel-Lindau disease. Extra-axial neoplasms include dermoid cysts, meningiomas, and schwannomas.

Clinically, posterior fossa lesions present with lethargy, vomiting, and headaches due to hydrocephalus or direct compression of the brainstem. Infants develop macrocephaly and the "setting-sun" sign, while older children exhibit ataxia.

Medulloblastoma

A high-grade tumor that progresses rapidly (in less than a month). On CT, it appears as a hyperdense mass in the cerebellar vermis with perifocal edema. On MRI, it is typically hypo- or isointense on T2WI and shows restricted diffusion on DWI (reflecting high cellularity). It is prone to leptomeningeal dissemination, making early scanning of the entire neuroaxis essential.

Astrocytoma and ependymoma

Cerebellar low-grade astrocytoma (CLGA) is a slow-growing tumor (most commonly pilocytic, WHO Grade I). It is characterized by a cystic structure with a contrast-enhancing mural nodule. On MRI, the solid component is hyperintense on T2WI. Unlike medulloblastoma, DWI shows no restricted diffusion.

Ependymoma (WHO Grade II) arises from the fourth ventricle and tends to "spill out" through the foramina of Luschka and Magendie. On MRI, it produces a hypointense signal on T1WI and an iso/hyperintense signal on T2WI, frequently containing microcysts, calcifications, and foci of hemorrhage.

Suprasellar tumors and brainstem gliomas

In the chiasmatic region, craniopharyngioma (WHO Grade I) is the most frequent. It typically has a mixed structure (cystic-solid) and contains calcifications. Clinically, it manifests with endocrine disorders (hypopituitarism) and visual deficits due to compression of the optic chiasm.

Brainstem tumors are divided into diffuse and focal exophytic types. Diffuse gliomas grow along the brainstem, exhibit a hyperintense signal on T2 and FLAIR, show mild contrast enhancement, and carry a poor prognosis (an H3 K27-M mutant form is now recognized). Focal tumors have clear margins, grow dorsally, and frequently enhance with contrast—these are typically Grade I-II astrocytomas with a better prognosis.

Class and exam questions

What else to study on this topic

• Molecular-genetic classification of medulloblastomas (WNT, SHH, groups 3 and 4)
• Signs of leptomeningeal metastasis
• Hypothalamic-optic pathway gliomas
• Atypical teratoid/rhabdoid tumor (AT/RT) and its differential diagnosis
• MR spectroscopy in high-grade tumors

Other Topics in "Pediatric Diagnostic Radiology"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.