CNS nontumor
Toxic and metabolic disorders
Radiation injury

Author: Kymberly A. Gyure, M.D. (see Authors page)

Revised: 18 August 2017, last major update November 2014

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Radiation injury CNS [title]

Cite this page: Gyure, K.A. Radiation injury. PathologyOutlines.com website. http://pathologyoutlines.com/topic/cnsradiationinjury.html. Accessed September 26th, 2017.
Definition / general
  • Radiation therapy is commonly used as adjuvant therapy for both primary and secondary malignant CNS neoplasms
  • Causes a spectrum of toxic CNS effects ranging from subclinical white matter injury to overt brain necrosis
Terminology
  • CNS lesions secondary to radiation therapy are typically classified based on their chronicity
    • Acute and subacute forms of radiation injury are due to blood brain barrier disruption and are generally reversible
    • Late or delayed radiation necrosis (develops months to years after irradiation) is a potentially disabling complication and is generally considered irreversible
Sites
  • White matter in field of previous radiation therapy
Pathophysiology
  • Primary mechansim of radiation necrosis is thought to be microvascular injury resulting in tissue hypoxia and necrosis
Clinical features
  • Neurologic symptoms depend on location of lesion and are essentially indistinguishable from symptoms due to a mass of any kind
  • In patients who have received radiation therapy for neoplasm, the principal clinical differential diagnosis is recurrent tumor
Diagnosis
  • Advanced imaging techniques including PET can suggest a diagnosis of radiation necrosis but biopsy / resection of questionable lesions is often performed to rule out recurrent tumor
Radiology description
  • Imaging studies demonstrate well demarcated, peripherally contrast enhancing lesions in white matter which are often difficult to distinguish from recurrent tumor
Radiology images

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Radiation necrosis of pons

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Abnormal enhancement in left occipital lobe

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Irregular enhancement around surgical cavity

Case reports
Treatment
  • Anti-VEGF therapy has been used successfully in some cases of CNS radiation necrosis but this is considered experimental
Gross description
  • Firm, ill defined mass or soft, friable lesion with cystic degeneration involving white matter
Microscopic (histologic) description
  • Fibrinoid necrosis or hyalinization / fibrosis of blood vessels, dystrophic calcification and an inflammatory infiltrate consisting predominantly of macrophages
  • Radiation induced cytologic atypia
Cytology description
  • As in other nonneoplastic CNS lesions, the presence of macrophages on intraoperative cytologic preparations should suggest the diagnosis of radiation necrosis over recurrent tumor
Differential diagnosis
  • Recurrence of the tumor for which the patient received radiation therapy (typically glioblastoma): features which favor radiation therapy effect include a lack of peripheral pseudopalisading of cells around areas of necrosis, the presence of associated microcalcifications and hyaline thickening of blood vessels