Tumors & Cysts

Astrocytomas

• • A slow-growing astrocytic tumor composed of bipolar “hair-like” (pilocytic) cells.
  • Most common glioma in children.
  • Associated with tuberous sclerosis, neurofibromatosis type 1 (NF1), and Li-Fraumeni syndrome.
    • Optic nerve and chiasm glioma are associated with NF1.
  • Often presents with symptoms of increased ICP (headache, nausea/vomiting), vision loss, ataxia, or cranial nerve deficits depending on location.
  • Imaging: Cystic mass with a contrast rim-enhancing nidus or mural nodule with minimal vasogenic edema, dorsally exophytic. Most commonly found in the cerebellum.
    • Also prefers midline structures such as the brainstem, optic chiasm, hypothalamus, and deep gray matter (basal ganglia).

      

  • KIAA1549-BRAF gene fusion is characteristic of this tumor type.

• • 90% 10-year overall survival. It can be treated with surgical resection alone, and rarely progresses to malignant glioma.
  • Classic patient presentation: Child presenting with increased ICP/ataxia, found to have a cerebellar cystic mass lesion with an enhancing mural nodule.

• Subependymal giant cell astrocytoma (SGCA or SEGA)

  • WHO grade 1 tumor almost exclusively seen in pediatric patients with tuberous sclerosis (TS) and before the age of 20.
    • Seen in 5-15% of patients with TS.
  • Often asymptomatic, but when symptomatic presents with obstructive hydrocephalus due to location in the foramen of Monro.
  • Imaging: Well-circumscribed, partially-calcified intraventricular contrast-enhancing mass near the foramen of Monro.

    

• • Generally treated initially with mTOR inhibition with everolimus.
    • If acute symptomatic or growing, can be treated with surgical resection.
  • Tuberous Sclerosis Review: classically presents with seizures, mental retardation, and adenoma sebaceum. Associated with TSC2/tuberin (most cases) or TSC1/hamartin with cortical or subependymal tubers, hamartomas, renal angiomyolipomas, and cardiac rhabdomyomas.

• Pleomorphic xanthoastrocytoma (PXA)

  • Found in young patients who present with temporal lobe epilepsy.
  • Imaging: Supratentorial peripheral cystic and contrast-enhancing mass abutting the leptomeninges with enhancing dural tail sign and scalloping of overlying bone.

• • Associated with BRAFV600E mutations and homozygous CDKN2A/B deletions.
  • Treated with surgical resection. However, local recurrence and malignant transformation are common so post-operative radiation is indicated for grade 3 tumors.

• Adult-type diffuse gliomas

  • • Astrocytoma, IDH-mutant (grades 2-4)
      • Patients present with progressive neurologic symptoms dependent on tumor location and/or with seizures.
      • Imaging: T2-FLAIR mismatch sign is often present, with T2 hyperintensity and relative hypointensity on FLAIR sequences.
        • MR Spectroscopy will have an elevated choline peak, low NAA peak, and elevated choline:creatinine ratio.
      • Pathology:
        • Grade 2: mitotic activity absent or low without microvascular proliferation, necrosis, or genetic markers that would upgrade the tumor (homozygous deletion of CDKN2A/B).
        • Grade 3:  mitotic activity present without microvascular proliferation, necrosis, or genetic markers that would upgrade the tumor.
          • Formally known as anaplastic astrocytoma.
        • Grade 4: microvascular proliferation, necrosis, or genetic markers that would upgrade the tumor present.
    • Glioblastoma, IDH-wildtype (grade 4)
      • Formally known as glioblastoma multiforme (GBM).
      • The most common and also most destructive of the diffuse gliomas.
      • Imaging: Contrast ring-enhancing lesions with significant vasogenic edema. Lesions can also have internal necrosis and can extend through the corpus callosum (butterfly lesion).

• • • • Genetics:
        • IDH-1/2 mutations are associated with secondary GBM arising from a lower-grade glioma.
        • Tumors without microvascular proliferation or necrosis can still be classified as “molecular” glioblastoma if genetic testing shows TERT promoter mutation, EGFR gene amplification, or gain of 7/loss of 10 chromosome copy number alterations.
      • Pathology: Cells with increased mitotic activity with pseudopalisading necrosis and microvascular endothelial proliferation.

• • • • Treatment: Maximal safe resection followed by intensity-modulated radiation therapy (IMRT) plus concomitant temozolomide (alkylating chemotherapy) followed by adjuvant temozolomide.
        • Methylation of the MGMT gene is associated with better treatment response to temozolomide.
        • Bevacizumab, a monoclonal antibody that inhibits vascular endothelial growth factor (VEGF)  can be used in recurrent or progressive GBM.
        • Another alkylating agent, lomustine, is often used as a second-line treatment or in recurrent gliomas.