Every year in the United States, more than three quarters of a million people have a stroke, and approximately every 3 minutes someone dies from a stroke. A significant portion of stroke victims are young, and left with a devastating handicap for the rest of their lives. The monetary and societal costs of stroke represent a major economic challenge to the healthcare system.  With stroke – as with heart attack – rapid treatment is essential to limit the extent of irreversible brain injury (“time-is-brain”), and rapid determination of the cause and degree of existing brain injury can be critical in deciding treatment.

CT perfusion imaging is a quick, widely available test that displays information about blood flow to the brain that can help diagnose, treat, and predict outcome in stroke patients.  When MRI is not readily available or contraindicated, CT perfusion imaging provides the best possible estimate of brain tissue likely to die without urgent, advanced therapies, including arterial “clot busting” drugs and blood clot retrieval devices.  CT perfusion imaging can also help classify reversible brain injury (“transient ischemic attacks”) that – like cardiac angina – may not require such immediate, aggressive treatment, as well as evaluate brain injury caused by arterial spasm due to bleeding from aneurysm rupture.

Published protocols for performing CT perfusion imaging at “as low a radiation dose as reasonably achievable” – a principle endorsed by the American College of Radiology and American Society of Neuroradiology – have circulated in the medical community for over a decade.  Strict protocol rules and oversight radiation protection personnel at most medical centers ensure that optimal image quality is maintained with a total radiation exposure often considerably lower than the current FDA recommended maximum dose.  Indeed, in an early, highly quoted study that compared different scanning protocols, it was shown that image quality is actually improved when CT perfusion is obtained at a lower average X-ray beam energy than is standard for routine CT imaging.

In all of medicine – and especially for stroke – the potential risks of any diagnostic test or therapeutic procedure (however rare) must be weighed against the very real benefits of preventing death or severe disability.  We believe, and the medical literature supports, that CT perfusion imaging, when appropriately performed, is justified and provides safe, valuable information that can substantially contribute to the management of acutely ill patients in an emergency setting.  Recent advances in scanner hardware and software, and the ongoing efforts of industry, offer the promise of further, significant reductions in CT radiation dose. The radiology community is committed to work hard towards this goal of reducing CT radiation dose, and continuing to offer the best imaging care to our patients.

References:

Janet C Miller, D. Phil., et al. CT Perfusion Imaging of the Brain. Radiology Rounds: A Newsletter for Referring Physicians from the Massachusetts General Hospital Department of Radiology. Volume 8, Issue 6, June 2010. http://www.mghradrounds.org/index.php?src=gendocs&ref=2010_june

Wintermark M, Lev MH. FDA investigates the safety of brain perfusion CT. AJNR Am J Neuroradiol. 2010 Jan;31(1):2-3.

Latchaw RE, Alberts MJ, Lev MH, Connors JJ, Harbaugh RE, Higashida RT, Hobson R, Kidwell CS, Koroshetz WJ, Mathews V, Villablanca P, Warach S, Walters B; American Heart Association Council on Cardiovascular Radiology and Intervention, Stroke Council, and the Interdisciplinary Council on Peripheral Vascular Disease. Recommendations for imaging of acute ischemic stroke: a scientific statement from the American Heart Association. Stroke. 2009 Nov;40(11):3646-78.

Wintermark M, Rowley HA, Lev MH. Acute stroke triage to intravenous thrombolysis and other therapies with advanced CT or MR imaging: pro CT. Radiology. 2009 Jun;251(3):619-26.

Wintermark M, Maeder P, Verdun FR, Thiran JP, Valley JF, Schnyder P, Meuli R. Using 80 kVp versus 120 kVp in perfusion CT measurement of regional cerebral blood flow. AJNR Am J Neuroradiol. 2000 Nov-Dec;21(10):1881-4.

Broad expert consensus on the minimum requirements for CT perfusion scan acquisition can be found in Table 2 (page E25) of the following paper, which can be freely downloaded from PubMed:

Wintermark M, Albers GW, Alexandrov AV, Alger JR, Bammer R, Baron JC, Davis S, Demaerschalk BM, Derdeyn CP, Donnan GA, Eastwood JD, Fiebach JB, Fisher M, Furie KL, Goldmakher GV, Hacke W, Kidwell CS, Kloska SP, Köhrmann M, Koroshetz W, Lee TY, Lees KR, Lev MH, Liebeskind DS, Ostergaard L, Powers WJ, Provenzale J, Schellinger P, Silbergleit R, Sorensen AG, Wardlaw J, Wu O, Warach S. Acute stroke imaging research roadmap. AJNR Am J Neuroradiol. 2008 May;29(5):e23-e30.

Before surgery, a chest radiograph was obtained and showed bilateral hilar nodularities.  Surgery was postponed and a chest CT confirmed the hilar abnormalities and showed parenchymal abnormalities (see below).  Based on the findings a work up for sarcoidosis was performed and was positive.  The patient received steroids and her vision improved.  Follow-up brain MRI showed the lesion to be smaller.

Sarcoidosis is more common in younger (average age: 35 years) African American women.  Over one half of patients will have neurological complaints, generally longstanding.  In about 10% of patients, sarcoidosis is isolated to the CNS.  The most common symptoms are headaches and cranial nerve palsies (mostly affecting the V, VII, VIII and III).  Approximately 15% of patients have dural disease (which is often accompanied by leptomeningeal involvement).  Dural disease responds well to treatment.  Conversely, intra-axial disease leads to seizures and is more difficult to control.  Angiotensin converting enzyme test is positive in 50% of patients.  The MRI findings on our case are typical of sarcoidosis.  The very low T2 signal can be seen in up 20% of meningiomas (particularly of the fibroblastic or transitional types).  Remember that most meningiomas are isointense to gray matter on T2WI (see below).

Suggested readings:

Chirstoforidis GA, Spickler EM, Recio MV, Mehta BM. MR of CNS sarcoidosis: correlation of imaging features to clinical symptoms and response to treatment. AJNR Am J Neuroradio 1999; 20: 655-669

Shag R. Roberson GH, Cure JK. Correlation of MR imaging findings and clinical manifestations in neurosarcoidosis. AJNR AM J Neurodiol 2009; 30: 953-961

Smith JK, Matheus MG, Castillo M. Imaging manifestations of neurosarcoidosis. AJR 2004; 182: 289-295

A 41-year-old female with history of migraine presented to the ED with acute onset of aphasia. In addition to the aphasia, there was numbness and tingling in the right arm and face. Patient demonstrated expressive aphasia and was not able to answer questions posed in the ED. Gadolinium MR perfusion images demonstrated decreased relative cerebral blood flow (top) in the left parietal/occipital lobes and increased time-to-peak (bottom) in the contralateral cerebellar hemisphere. Although crossed cerebellar diaschisis (CCD) is seen mostly on radiotracer studies (hypometabolism on PET studies), it was nicely demonstrated in our patient. CCD occurs more often after supratentorial infarctions but has been reported in the setting of migraine. This phenomenon occurs immediately after brain injury due to the large number of functional connections between cerebrum and cerebellum. In reverse CCD, the brain abnormality is due to injury of the cerebellum. Because of the limited number of slices on perfusion MR studies, particularly when using ASL techniques, it is important to keep in mind that the cerebellum may be involved in several supratentorial abnormalities and needs to be included in the study.  I would be interested in finding out if anyone else has seen this type of migraine-associated CCD.