Rationale and Objectives
Delayed cerebral ischemia (DCI) is a devastating condition that occurs secondary to aneurysmal subarachnoid hemorrhage (A-SAH). The purpose is to compare computed tomography perfusion (CTP) and digital subtraction angiography (DSA) for determining DCI in A-SAH.
Materials and Methods
A retrospective study of A-SAH patients admitted at our institution between December 2004 and December 2008 was performed. CTP and DSA were obtained at days 6–8 after aneurysm rupture. Both qualitative and quantitative analyses of CT perfusion deficits were performed. DSA was categorized as presence or absence of vasospasm. The reference standard for determining DCI was based on clinical deterioration or infarction on CT or MRI. The test characteristics of CTP and DSA were calculated and their graphs of conditional probabilities were constructed using Bayesian analysis.
Results
Fifty-seven patients were included; 79% (45/57) had DCI. Seventy percent (40/57) had CTP perfusion deficits; 80% (36/45) of the DCI and 33% (4/12) of no DCI patients. Sixty-three percent (36/57) had DSA demonstrating vasospasm; 73% (33/45) of the DCI and 25% (3/12) of no DCI patients. Quantitative analysis of the CTP data revealed a significant difference in cerebral blood flow values for the DCI (29.4 mL/100 g/minute) and no DCI groups (40.5 mL/100 g/minute, P = .0213). The sensitivity, specificity, and positive and negative predictive values for CTP were 0.80 (95% CI 0.68–0.92), 0.67 (95% CI 0.40–0.93), 0.90 (95% CI 0.82–0.96), 0.47 (95% CI 0.27–0.62), and for DSA were 0.73 (95% CI 0.60–0.86), 0.75 (95% CI 0.50–0.99), 0.92 (95% CI 0.82–0.98), and 0.43 (95% CI 0.26–0.53), respectively.
Conclusion
CTP and DSA have similar test characteristics and Bayesian analysis for determining DCI in A-SAH patients.
Cerebral vasospasm is a significant cause of morbidity in patients with aneurysmal subarachnoid hemorrhage (A-SAH), occurring in 20%–50% of patients after successful surgical or endovascular treatment of the ruptured aneurysm . Several terms have been used in the literature to describe this entity, including symptomatic vasospasm, angiographic vasospasm, transcranial Doppler vasospasm, and delayed cerebral ischemia (DCI). In the past, the gold standard for vasospasm has been accepted as arterial narrowing documented on digital subtraction angiography (DSA). However, the presence of angiographic vasospasm does not always correlate with neurological deterioration or the development of infarction .
Conversely, DCI has been shown to be the most clinically relevant term because of its strong associations with poor clinical outcome measures such as cognitive impairment and reduced quality of life . DCI is defined as an otherwise unexplained clinical deterioration and/or new infarction demonstrated on imaging examinations. Clinical deterioration may manifest by alterations in consciousness, worsening on Glasgow coma scale, or new neurologic deficits. Other potential causes of clinical deterioration, such as hemorrhage, seizure activity, or hydrocephalus, are not included in this definition. The second component of DCI is the presence of a new infarction documented on imaging examinations. This definition does not include infarctions present on the admission or the immediate postoperative imaging exams . An important limitation to using this definition in clinical practice is that the diagnosis of DCI is retrospectively obtained once a neurologic deficit or infarction has already occurred. As a result, interventions to reduce the subsequent morbidity and mortality may have limited usefulness . It has also been reported that the presence of DCI is associated with a more complicated hospital course resulting in prolonged hospitalization and extended length of stay in the intensive care unit . Thereby, assessing the probability of a patient with DCI prior to developing a permanent neurological deficit and/or infarction is important for identifying patients that will maximally benefit from medical or interventional treatment.
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Materials and methods
Study Population
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Study Design
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CTP Scanning Protocol and Data Processing
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DSA
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Reference Standard
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Statistical Analysis
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Results
Study Population Characteristics
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Table 1
Clinical and Demographic Characteristics of the Study Population
Study Population n = 57 All
n = 57 DCI
n = 45 No DCI
n = 12 Age (years) median
range 51 28–80 55 29–80 48 28–78 Gender % (n) % (n) % (n) Male 25 (14/57) 27 (12/45) 17 (2/12) Female 75 (43/57) 73 (33/45) 83 (10/12) Aneurysm location Anterior 95 (54/57) 93 (42/45) 100 (12/12) Posterior 5 (3/57) 7 (3/45) 0 (0/12) Treatment type Surgical clipping 65 (37/57) 62 (28/45) 75 (9/12) Coil embolization 35 (20/57) 38 (17/45) 25 (3/12) Hunt Hess grade Low (Grades 1 and 2) 46 (26/57) 44 (20/45) 50 (6/12) High (Grades 3, 4, and 5) 54 (31/57) 56 (25/45) 50 (6/12)
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Table 2
Imaging Characteristics of the Study Population
Study Population (n = 57) All
n = 57 DCI
n = 45 No DCI
n = 12 Day of CTP median 7 7 6 Qualitative CTP deficit % (n) 70 (40/57) 80 (36/45) 33 (4/12) Time-frame between symptoms and CTP in days median 0 0 0 Day of DSA median 8 8 9 Timeframe between CTP and DSA in days median 1 1 3
CTP, computed tomography perfusion; DSA, digital subtraction angiography.
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Table 3
Comparison of Test Characteristics for CTP and DSA
CTP DSA Sensitivity 0.80 (95% CI 0.68–0.92) 0.73 (95% CI 0.60–0.86) Specificity 0.67 (95% CI 0.40–0.93) 0.75 (95% CI 0.50–0.99) PPV 0.90 (95% CI 0.82–0.96) 0.92 (95% CI 0.82–0.98) NPV 0.47 (95% CI 0.27–0.62) 0.43 (95% CI 0.26–0.53) LR + 2.4 (95% CI 1.06–5.41) 2.9 (95% CI 1.08–7.94) LR - 0.3 (95% CI 0.15–0.61) 0.4 (95% CI 0.20–0.64) Odds ratio 8.0 (95% CI 1.96–32.6) 8.25 (95% CI 1.91–35.67)
CTP, computed tomography perfusion; DSA, digital subtraction angiography; LR +, likelihood ratio of a positive result; LR -, likelihood ratio of a negative result; NPV, negative predictive value; PPV, positive predictive value.
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Discussion
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Conclusion
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