= GBM

Most malignant form of all gliomas / astrocytomas; end stage of progressive severe anaplasia of preexisting Grade I / II astrocytoma (not from embryologic glioblasts)

Incidence: most common primary brain tumor; 50% of all intracranial tumors; 1–2% of all malignancies; 20,000 cases per year

Age: all ages; peak incidence at 65–75 years; M÷F = 3÷2; more frequently in whites

Genetics: Turcot syndrome, neurofibromatosis type 1, Li-Fraumeni syndrome (familial neoplasms in various organs based on abnormal p53 tumor-suppressor gene)

Path: multilobulated appearance; quite extensive vasogenic edema (transudation through structurally abnormal vascular tumor channels); deeply infiltrating neoplasm; hemorrhage; necrosis is essential for pathologic diagnosis (HALLMARK)

Histo: highly cellular, often bizarrely pleomorphic / undifferentiated multipolar astrocytes; common mitoses + prominent vascular endothelial proliferation; no capsule; pseudopalisading (= viable neoplastic cells form an irregular border around necrotic debris as the tumor outgrows its blood supply)

Subtypes:

1. giant cell GBM = monstrocellular sarcoma
2. small cell GBM = gliosarcoma = Feigin tumor

Location:

1. hemispheric: white matter of centrum semiovale: frontal >temporal lobes; common in pons, thalamus, quadrigeminal region; relative sparing of basal ganglia + gray matter
   DDx: solitary metastasis, tumefactive demyelinating lesion (“singular sclerosis”), atypical abscess
2. callosal: “butterfly glioma” may grow exophytically into ventricle
3. posterior fossa: pilocytic astrocytoma, brainstem astrocytoma
4. extraaxial: primary leptomeningeal glioblastomatosis
5. multifocal: in 2–5%

Spread:

1. direct extension along white matter tracts:
   corpus callosum (36%), corona radiata, cerebral peduncles, anterior commissure, arcuate fibers
   • readily crosses midline = “butterfly” glioma (clue: invasion of septum pellucidum)
   • frontal + temporal gliomas tend to invade basal ganglia
   • may invade pia, arachnoid and dura (mimicking meningioma)
2. subependymal carpet after reaching surface of ventricles
3. via CSF (<2%)
4. hematogenous (extremely rare):
   • osteoblastic bone lesion

NECT:

• inhomogeneous low-density mass with irregular shape + poorly defined margins (hypodense solid tumor / cavitary necrosis / tumor cyst / peritumoral “fingers of edema”)
• considerable mass effect → compression + displacement of ventricles, cisterns, brain parenchyma
• iso- / hyperdense portions (= hemorrhage) in 5%
• rarely calcifies (if coexistent with lower-grade glioma / after radio- or chemotherapy)

CECT:

Enhancement pattern: contrast enhancement ← breakdown of blood-brain barrier / neovascularity / areas of necrosis

1. diffuse homogeneous enhancement
2. heterogeneous enhancement
3. ring pattern (occasionally enhancing mass within the ring)
4. low-density lesion with contrast-fluid level ← leakage of contrast

• almost always ring blush of variable thickness: multiscalloped (“garland”), round / ovoid; may be seen surrounding ventricles (= subependymal spread); tumor usually extends beyond margins of enhancement
• sedimentation level ← cellular debris / hemorrhage / accumulated contrast material in tumoral cyst

MR:

• poorly defined lesion with some mass effect / vasogenic edema / heterogeneity
• hemosiderin deposits (gradient echo images)
• hemorrhage (= hypointensity on T2WI and T2*WI)
• T1WI + gadolinium-DTPA enhancement separates tumor nodules from surrounding edema, central necrosis and cyst formation

Angio:

• wildly irregular neovascularity + early draining veins
• avascular lesion

PET:

• increase in glucose utilization rate

Rx: surgery + radiation therapy + chemotherapy

Prognosis: 16–18 months postoperative survival (frequent tumor recurrence ← during surgery uncertainty about tumor margins)