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Radiation and Chemotherapy


KEY FACTS

Terminology

  • Radiation-induced injury may be divided into acute, subacute/early delayed, late injury

Imaging

  • Radiation injury : Mild vasogenic edema to necrosis

  • Radiation necrosis : Irregular enhancing lesion(s)

    • MRS: Markedly ↓ metabolites (NAA, Cho, Cr), ± lactate/lipid peaks

    • Perfusion MR: ↓ relative cerebral blood volume compared with tumor

  • Leukoencephalopathy : T2 white matter (WM) hyperintensity, spares subcortical U fibers

  • Mineralizing microangiopathy : Basal ganglia, subcortical WM Ca++, atrophy

  • Necrotizing leukoencephalopathy : WM necrosis

  • PRES : Posterior circulation subcortical WM edema

  • MRS, MR perfusion, PET, or SPECT may help delineate recurrent tumor from radiation necrosis

Top Differential Diagnoses

  • Neoplasm

  • Abscess

  • Multiple sclerosis

  • Vascular dementia

  • Progressive multifocal leukoencephalopathy

Pathology

  • 2nd neoplasms: Meningiomas (70%), gliomas (20%), sarcomas (10%)

    • More aggressive tumors, highly refractory

    • Incidence: 3-12%

  • Radiation-induced vascular malformations: Capillary telangiectasias ± cavernomas

Clinical Issues

  • Overall incidence of radionecrosis: 3-9%

  • Worse prognosis: Younger patient at treatment

Axial NECT shows extensive calcification in the subcortical white matter (WM)
in a 20-year-old patient. Mineralizing microangiopathy usually results after a combination of radiation therapy and chemotherapy 2 or more years after treatment.

Axial SWI in an adult patient with neurofibromatosis and optic nerve glioma status post radiation therapy in childhood shows innumerable “blooming” hypointense foci
consistent with radiation-induced vascular malformations.

Axial FLAIR MR in a 22 year old with acute leukemia treated with intrathecal methotrexate shows confluent periventricular and deep WM hyperintensities
with sparing of the subcortical WM.

Axial T1 C+ MR in the same patient shows multiple nodular enhancing lesions in the WM
. Findings are consistent with chemotherapy-induced necrotizing leukoencephalopathy. Leukoencephalopathy is a potentially serious complication of chemotherapy.

TERMINOLOGY

Abbreviations

  • Radiation-induced injury (RII)

Synonyms

  • Radiation (XRT) changes, chemotherapy effects, treatment-related changes

Definitions

  • RII may be divided into acute (during or shortly after radiation), subacute/early delayed (typically up to 12 weeks after radiation), and late (months to years after completion of radiation)

  • Includes radiation injury (edema, arteritis), radiation necrosis, leukoencephalopathy, mineralizing microangiopathy, necrotizing leukoencephalopathy, posterior reversible encephalopathy syndrome (PRES), radiation-induced tumors

IMAGING

General Features

  • Best diagnostic clue

    • Radiation injury: Mild vasogenic edema to necrosis

    • Radiation necrosis: Irregular enhancing lesion(s)

    • Leukoencephalopathy: T2 white matter (WM) hyperintensity, spares subcortical U-fibers

    • Mineralizing microangiopathy: Basal ganglia (BG), subcortical WM Ca++, atrophy

    • Necrotizing leukoencephalopathy (NLE): WM necrosis ± Ca++

    • PRES: Posterior circulation subcortical WM edema

  • Location

    • Radiation injury occurs in radiation port

    • Periventricular WM especially susceptible

    • Subcortical U-fibers and corpus callosum spared

CT Findings

  • NECT

    • Acute RII: Usually normal or transient diffuse brain swelling

    • Subacute/early delayed RII: Confluent WM low-density edema

    • Late RII: Focal/multiple WM low density

    • Leukoencephalopathy : Symmetric WM hypodensity

    • Mineralizing microangiopathy : BG, subcortical WM Ca++, atrophy

    • NLE : Extensive areas of WM necrosis, Ca++

    • PRES : Subcortical WM edema, posterior circulation

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