title: Intracranial metastatic disease spares the limbic circuit: a review of 697 metastatic lesions in 107 patients.
abstract: OBJECTIVE
  We report the incidence of metastatic involvement of the limbic circuit in a retrospective review of patients treated at our institution. This review was performed to assess the feasibility of selectively sparing the limbic system during whole-brain radiotherapy and prophylactic cranial irradiation.
  
  
  METHODS
  We identified 697 intracranial metastases in 107 patients after reviewing contrast-enhanced CT and/or MR image sets for each patient. Lesions were localized to the limbic circuit or to the rest of the brain/brain stem. Patients were categorized by tumor histology (e.g., non-small-cell lung cancer, small-cell lung cancer, breast cancer, and other) and by total number of intracranial metastases (1-3, oligometastatic; 4 or more, nonoligometastatic).
  
  
  RESULTS
  Thirty-six limbic metastases (5.2% of all metastases) were identified in 22 patients who had a median of 16.5 metastases/patient (limbic metastases accounted for 9.9% of their lesions). Sixteen metastases (2.29%) involved the hippocampus, and 20 (2.86%) involved the rest of the limbic circuit; 86.2% of limbic metastases occurred in nonoligometastatic patients, and 13.8% occurred in oligometastatic patients. The incidence of limbic metastases by histologic subtype was similar. The incidence of limbic metastases in oligometastatic patients was 4.9% (5/103): 0.97%, hippocampus; 3.9%, remainder of the limbic circuit. One of 53 oligometastatic patients (1.9%) had hippocampal metastases, while 4/53 (7.5%) had other limbic metastases.
  
  
  CONCLUSIONS
  Metastatic involvement of the limbic circuit is uncommon and limited primarily to patients with nonoligometastatic disease, supporting our hypothesis that it is reasonable to selectively exclude or reduce the dose to the limbic circuit when treating patients with prophylactic cranial irradiation or whole-brain radiotherapy for oligometastatic disease not involving these structures.
authors.affiliation: Department of Radiation Oncology, Rush University Medical Center, Chicago, Illinois, USA. james_marsh@rush.edu
authors.forename: James C
authors.initials: JC
authors.lastname: Marsh
authors.forename: Arnold M
authors.initials: AM
authors.lastname: Herskovic
authors.forename: Benjamin T
authors.initials: BT
authors.lastname: Gielda
authors.forename: Frank F
authors.initials: FF
authors.lastname: Hughes
authors.forename: Thomas
authors.initials: T
authors.lastname: Hoeppner
authors.forename: Julius
authors.initials: J
authors.lastname: Turian
authors.forename: Ross A
authors.initials: RA
authors.lastname: Abrams
mesh_terms: D001932:Brain Neoplasms / Q000453:epidemiology / Q000517:prevention & control / Q000556:secondary*; D001943:Breast Neoplasms / Q000556:secondary; D002289:Carcinoma, Non-Small-Cell Lung / Q000556:secondary; D016371:Cranial Irradiation / Q000379:methods*; D005240:Feasibility Studies; D005260:Female; D006624:Hippocampus; D006801:Humans; D015994:Incidence; D008032:Limbic System; D008175:Lung Neoplasms / Q000473:pathology; D008297:Male; D012189:Retrospective Studies; D055752:Small Cell Lung Carcinoma / Q000556:secondary