Pediatric Astrocytoma Workup

Updated: Aug 18, 2017
  • Author: Lauren R Weintraub, MD; Chief Editor: Max J Coppes, MD, PhD, MBA  more...
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Workup

Imaging Studies

The following studies are indicated in patients with suspected astrocytoma:

  • Head CT imaging with and without contrast

    • CT imaging has higher than 95% sensitivity for the detection of brain tumors.

    • On CT scans, most supratentorial low-grade astrocytomas are hypodense with variable contrast enhancement. Calcifications may be present. High-grade tumors show a more heterogeneous density pattern and a more diffuse contrast enhancement.

    • Patients with cerebellar astrocytomas may demonstrate hydrocephalus and contrast enhancement on CT scans. A prominent cystic component is often present.

    • Brainstem astrocytomas typically enhance poorly after contrast and lack calcifications on CT scans. They may appear isodense or hypodense.

  • Head and spine MRI with and without gadolinium

    • MRI is the imaging modality of choice for brainstem astrocytomas. See the images shown below.

      This MRI shows a pilocytic astrocytoma of the cere This MRI shows a pilocytic astrocytoma of the cerebellum.
      This MRI shows a supratentorial glioblastoma multi This MRI shows a supratentorial glioblastoma multiforme.
    • MRI of the head must be performed in all patients with CT scan or clinical findings consistent with astrocytoma. Other tumors, such as medulloblastoma and ependymoma, may have a similar appearance on CT scans. MRI is useful in such instances by better demonstrating the anatomic origin and extent of tumor.

    • MRI is the imaging modality of choice for detecting primary or disseminated spinal cord lesions. Perform an MRI of the spine in all tumors with malignant characteristics.

    • A postoperative MRI is required to measure the extent of surgical resection and the detection of residual disease. Postoperative MRI evaluation must be performed within 72 hours of surgery in order to delineate residual tumor from the postsurgical inflammatory changes that are visualized on MRI at this time.

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Procedures

See the list below:

  • CSF cytological examination: This examination is useful in malignant astrocytomas for the detection of microscopic leptomeningeal dissemination.

  • Lumbar puncture: CT imaging or MRI must be performed prior to the lumbar puncture (LP) to rule out the presence of hydrocephaly in those patients suspected of having a brain tumor. Hydrocephaly places the patient at risk for herniation as a consequence of the procedure. In general, the LP is deferred as long as 2 weeks postoperatively in order to avoid identifying tumor cells that may have disseminated as a result of surgery.

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Histologic Findings

See the list below:

  • Childhood astrocytomas represent different histopathologic entities, such as pure astrocytoma (commonly pilocytic and fibrillary type in children), oligodendroglioma, and mixed tumors of both cell types. Astrocytomas are composed of glial fibrillary acidic protein (GFAP)–positive bipolar or stellate cells. Oligodendrogliomas are characterized by monotonous collections of spheroidal cells. The classification of gliomas is based primarily on their degree of anaplasia, rather than on histologic type.

  • Tumors that are modestly cellular and contain few or none of the histologic criteria of malignancy are designated low-grade or grade I and II lesions, according to the WHO. Unifying features are their slowly evolving nonaggressive clinical behavior and relatively benign histological appearance.

  • Grade I is primarily designated for the typical pilocytic astrocytoma (see image below), accounting for 85% of cerebellar low-grade gliomas. [7] It is composed of astrocytes interwoven with a fine fibrillary background and often has a characteristic microcystic component and Rosenthal fibers. The newly described pilomyxoid variant of low-grade astrocytoma has unusual histologic features, including abundance of myxoid background, the absence of Rosenthal fibers, and the presence of an angiocentric pattern. Whether or not this is a variant of pilocytic astrocytoma or a distinct entity remains unclear. Grade II is reserved for diffuse astrocytomas composed of moderately cellular astrocytes, oligodendrocytes, or both.

    This section displays the typical biphasic pattern This section displays the typical biphasic pattern of a pilocytic astrocytoma, consisting of dense, relatively anuclear, fibrillar areas alternating with looser cystic fields.
  • High-grade tumors are characterized by the presence of several histologic features of malignancy that include hypercellularity, cytologic and nuclear atypia, mitoses, necrosis, and endothelial proliferation (see top image below). These tumors are clinically aggressive, regionally invasive, and capable of neuraxial dissemination. Grade III refers to anaplastic astrocytoma (see top image below) and grade IV is designated for glioblastoma multiforme (see bottom image below).

    This section displays the high cellularity, mitosi This section displays the high cellularity, mitosis, and nuclear atypia characteristic of an anaplastic astrocytoma (grade III).
    This section displays a typical field of a gliobla This section displays a typical field of a glioblastoma multiforme (grade IV) with pseudopalisading neovascularity, nuclear atypia, numerous mitoses, and areas of hemorrhage.
  • The most common lesions of the brain stem are diffuse midline gliomas (80%), previously referred to as diffuse intrinsic pontine gliomas (DIPGs), and characterized by an H3K27M mutation and carry an extremely poor prognosis. [8] Exophytic tumors arising from the brain stem are more likely to be low-grade.

See Brain Cancer Staging for summarized information.

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