title: MR imaging and HMPAO scintigraphy in conjunction with balloon test occlusion: value in predicting sequelae after permanent carotid occlusion.
abstract: OBJECTIVE
  Permanent occlusion of the internal carotid artery may be required for en bloc resection of a neck tumor or to treat certain aneurysms. The risk of ischemic infarct is usually assessed with carotid balloon test occlusion and concurrent distal arterial pressure measurement. However, up to 20% of patients who tolerate the test occlusion have delayed neurologic sequelae. We propose enhanced MR imaging and hexamethylpropyleneamine oxime (HMPAO) scintigraphy to detect subclinical signs of ischemia and hypoperfusion as adjuncts to the balloon test occlusion to identify patients at risk for delayed sequelae.
  
  
  METHODS
  We prospectively examined 12 patients referred for balloon test occlusion of the carotid artery. Serial measurements of distal occluded internal carotid pressure were recorded. 99mTc-HMPAO was injected IV after 2 min of asymptomatic test occlusion, and single-photon emission computed tomographic (SPECT) data acquisition was done 1-6 hr later. Contrast-enhanced MR imaging was performed 1-8 hr after completion of the 30-min test occlusion. Signs of decreased perfusion or ischemia on these tests were compared with the mean distal arterial pressure and neurologic status of the patient during test occlusion.
  
  
  RESULTS
  Seven (58%) of 12 patients had abnormal findings on HMPAO scintigraphy or contrast-enhanced MR imaging. Only one patient had neurologic deficits that corresponded to abnormal MR enhancement. The other 11 patients (92%) remained asymptomatic during the 30-min test occlusion. Of these 11 asymptomatic patients, five (45%) had areas of decreased perfusion on scintigraphy and three (27%) had abnormal MR contrast enhancement suggesting residual focal ischemia as a result of the test occlusion. Mean arterial pressures in the distal occluded artery did not correlate well with the imaging results.
  
  
  CONCLUSIONS
  HMPAO scintigraphy can show clinically silent areas of decreased perfusion, while enhanced MR shows signs of acute ischemia (i.e., significant hypoperfusion) associated with asymptomatic balloon test occlusion. Theoretically, such patients would be at increased risk for permanent sequelae after permanent carotid occlusion.
authors.affiliation: Department of Radiology, University of Iowa College of Medicine, Iowa City 52242.
authors.forename: T M
authors.initials: TM
authors.lastname: Simonson
authors.forename: T J
authors.initials: TJ
authors.lastname: Ryals
authors.forename: W T
authors.initials: WT
authors.lastname: Yuh
authors.forename: G P
authors.initials: GP
authors.lastname: Farrar
authors.forename: K
authors.initials: K
authors.lastname: Rezai
authors.forename: H T
authors.initials: HT
authors.lastname: Hoffman
mesh_terms: D000328:Adult; D000368:Aged; D001921:Brain / Q000000981:diagnostic imaging / Q000473:pathology; D002545:Brain Ischemia / Q000175:diagnosis / Q000453:epidemiology*; D002343:Carotid Artery, Internal; D002404:Catheterization; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003097:Collateral Circulation / Q000502:physiology; D005260:Female; D006258:Head and Neck Neoplasms / Q000601:surgery; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015609:Organotechnetium Compounds; D010091:Oximes; D011183:Postoperative Complications / Q000517:prevention & control; D011446:Prospective Studies; D012307:Risk Factors; D019690:Technetium Tc 99m Exametazime; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D015609:Organotechnetium Compounds; D010091:Oximes; D019690:Technetium Tc 99m Exametazime