Primary Brain Neoplasms

Primary Brain Neoplasms

Todd M. Blodgett, MD

Alex Ryan, MD

Marios Papachristou, MD

Axial FLAIR MR shows abnormal signal image in a patient with a glioblastoma multiforme treated with gamma knife. Differential is radiation necrosis vs. recurrent tumor.

Axial PET shows correlative intense FDG activity image, compatible with residual/recurrent tumor rather than radiation necrosis.


Abbreviations and Synonyms

  • Low grade gliomas (LGG)

  • Astrocytomas

  • Glioblastoma multiforme (GBM)

  • Other primary brain neoplasms


  • Imaging of neoplasms of glial or astrocyte origin

  • World Health Organization (WHO) grade I

    • Most are benign

    • Example: Pilocytic astrocytoma

  • WHO grade II

    • Benign to semi-benign

    • Example: Astrocytoma and oligoastrocytoma

  • WHO grade III

    • Semi-benign to malignant

    • Example: Astrocytoma

  • WHO grade IV

    • Malignant

    • Example: GBM

    • Two types

      • Primary (de novo)

      • Secondary (degeneration from lower grade tumors)


General Features

  • Best diagnostic clue

    • MR shows variable amounts of enhancement

      • Most low grade gliomas show little if any enhancement

      • High grade tumors show extensive enhancement

    • MRS shows abnormal choline-to-creatine (Cho:Cr) ratio and decreased N-acetylaspartate (NAA)

    • FDG PET shows little activity in low grade gliomas and increasing amounts of FDG uptake in higher grade tumors

  • Location

    • Intra-axial

    • 2/3 supratentorial and 1/3 infratentorial for low grade gliomas

    • Most anaplastic astrocytomas and GBMs are hemispheric

  • Size

    • Variable, from a few millimeters to several centimeters

    • Smaller tumors < 6 mm often not visualized by FDG PET

  • Morphology

    • Variably sized intra-axial tumor ± enhancement with surrounding vasogenic edema

    • Gliomas tend to be diffuse without sharp border, especially WHO grade II tumors

Imaging Recommendations

  • Best imaging tool

    • MR is first choice to show location and extent of tumor

    • MR

      • Primary tumor usually demonstrates extent of enhancement

      • Low grade tumors may not show abnormal enhancement

      • FLAIR images show extent of vasogenic edema

      • May show mass effect, hemorrhage, necrosis, and signs of increased intracranial pressure

    • FDG PET

      • Increased uptake in pilocytic astrocytomas and higher grade gliomas & astrocytomas

      • Can estimate grade and malignancy of tumor before operation, as well as show tumor extent and heterogeneity

  • Protocol advice

    • FDG PET

      • Minimize auditory and visual stimulation during FDG uptake phase

      • Dynamic acquisition

  • Additional nuclear medicine imaging options

    • SPECT

  • Other PET tracers for neurooncology (investigational)

    • C-11 Methionine: Amino acid transport

    • C-11 Tyrosine: Amino acid transport

    • C-11 Choline: Membrane synthesis, proliferation

    • F-18 Fluorothymidine: Proliferation

  • Correlative imaging features

    • CT: Variable appearance, difficult to see without contrast unless large

    • MR: Most primary CNS tumors will show some enhancement, except low grade gliomas (grade I-II); usually accompanied by vasogenic edema

CT Findings

  • General

    • NECT

      • Ill-defined mass occasionally with calcifications (up to 20% in LGG, rare in anaplastic and GBM)

      • Often mass may not be visible on a noncontrast study

    • CECT

      • Low grade gliomas should have no enhancement

      • GBM will typically enhance and may have necrosis centrally

  • GBM

    • NECT

      • Irregular isodense or hypodense mass with central hypodensity representing necrosis

      • Marked mass effect and surrounding edema/tumor infiltration

      • Hemorrhage not uncommon

      • Calcification rare (related to low grade tumor degeneration)

    • CECT

      • 95% have strong heterogeneous irregular rim enhancement

  • Low grade astrocytoma

    • NECT

      • Ill-defined homogeneous hypo-/isodense mass

      • 20% calcified; cysts are rare

      • Calvarial erosion in cortical masses (rare)

  • CECT

    • No enhancement or very minimal

      • Enhancement should raise suspicion of focal malignant degeneration

MR Findings


    • Typically will show a larger area of involvement representing edema

  • T1 C+

    • No enhancement with low grade tumor

    • Variable amounts of enhancement, mass effect, and central necrosis with GBM

  • MRS

    • Elevated Cho:Cr ratio and decreased NAA

  • CNS lymphoma, high grade glioma, and metastatic tumor show enhancement on MR

Nuclear Medicine Findings

  • Metabolic activity in primary glial and astrocytic tumors correlates with tumor grade and prognosis

  • Low grade gliomas show mild FDG uptake

    • Generally more than normal white matter, much less than normal cortex

  • Higher grade tumors have increasing FDG activity, with GBM being very FDG avid, as much or more than normal cortex

  • PET/CT neuronavigation-guided surgery can achieve total tumor resection in 31% of cases vs. 19% in conventional operation

  • High grade gliomas show significantly higher SUV average and SUV maximum than metastatic tumors

    • However, considerable overlap between these two tumors exists

    • FDG accumulation alone is unlikely to be adequate in clinical setting

  • SUV max of 15 used for cutoff of high grade glioma and lymphoma

  • Using cutoff SUV of 15, lymphoma can be excluded, and differential can be narrowed to high grade glioma vs. metastatic brain tumor

  • SUV max most accurate parameter for distinguishing CNS lymphoma from other brain tumors

    • CNS lymphoma typically has highest uptake of primary brain tumors

  • SUV in primary brain tumor dependent on variety of factors

    • Plasma glucose level, steroid treatment, tumor size and heterogeneity, time after injection, and previous irradiation

    • Steroid treatment may decrease FDG uptake in CNS lymphoma



  • Primary cannot be differentiated from a metastatic lesion by imaging

    • Whole-body FDG PET can help identify primary lesion if outside the brain

  • Multiple ring-enhancing lesions

  • History of malignancy makes this diagnosis the most likely


  • Usually cannot be differentiated by imaging

  • Patients usually have other infectious symptoms such as fever and elevated white blood cell count


  • Little or no FDG uptake

  • May conform to a vascular distribution

Multiple Sclerosis (MS)

  • Tumefactive MS can look similar to an intracranial neoplasm

Radiation Necrosis

  • PET negative in most cases

  • In contrast, high grade tumors tend to have increased levels of FDG uptake


  • Usually multiple smaller areas of involvement

  • Usually no enhancement


General Features

  • Genetics: Loss, mutation, or hypermethylation of tumor suppressor gene TP53

  • Etiology: Variable

  • Epidemiology

    • Gliomas

      • Incidence is 6-8/100,000, with 50% being malignant subtypes

    • GBM

      • 3-4/100,000; ≈ 50% of all gliomas are GBM

    • Younger patients tend to have lower grade gliomas with grade increasing in older age groups

Gross Pathologic & Surgical Features

  • Tumor is difficult to distinguish from normal or edematous brain tissue at operation

    • Percentage of complete removal by routine surgery is disappointing, leading to poor prognosis

    • Genuine total removal of glioma probably impossible because of diffuse growth and location

Microscopic Features

  • Grade depends on

    • Degree of cellularity

    • Cellular pleomorphism

    • Mitotic figures

    • Necrosis

    • Vascular proliferation



  • Most common signs/symptoms

    • Various neurologic symptoms

      • Headaches

      • Seizures

      • Visual disturbances

  • Other signs/symptoms: Other symptoms related to mass effect or hemorrhage


Sep 22, 2016 | Posted by in MAGNETIC RESONANCE IMAGING | Comments Off on Primary Brain Neoplasms
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