Multidetector Computerized Tomography for the Evaluation of Cerebrovascular Disease: A Case Study

Case Report

The patient is a 59-year-old hypertensive, diabetic, white male ex-smoker with a history of CABG in 1994. In 1997, he underwent insertion of a pacemaker for bradycardia. In 1999, he presented with hoarseness and was diagnosed with squamous cell laryngeal cancer by biopsy. He underwent laryngeal irradiation from 3/99 to 5/99 and required insertion of a PEG tube relating to his irradiation. He stopped smoking at that time. He did well until 5/03, at which time he complained of some worsening dysphonia, dizziness and diplopia. Workup at that time revealed hypothyroidism that was successfully treated with levothyroxin by 7/03/03. Despite that, he continued to have visual disturbance and changes in his voice. Interestingly, he complained of double vision only in his left visual field. An ophthalmologic exam failed to explain his visual symptoms and a neurological evaluation was suggested. After examination by the neurologist, a craniocervical computerized tomographic angiogram (CTA) and intracranial MRI was ordered. The CTA study was performed using a Philips Mx8000-IDT 16-slice multidetector computerized tomographic (MDCT) scanner. The study identified several relevant findings, including an aberrant origin of the left vertebral artery from the aortic arch with moderate to severe origin stenosis; right internal carotid artery occlusion; 60% stenosis of the left internal carotid artery and severe basilar artery stenosis. MRI demonstrated chronic infarct of the right occipital lobe that was not apparent on a head CT performed 3 months earlier. Further characterization of the vascular anatomy was desired for possible intervention, and a 4-vessel cerebral arteriogram was performed. The angiogram confirmed right internal carotid artery occlusion, left internal carotid stenosis and severe long basilar artery stenosis. Adequate aortic arch views were not obtained to visualize the aberrant vertebral origin. The patient’s basilar artery stenosis was deemed too risky for intervention and he was treated with warfarin and aspirin. Approximately six months later, the patient developed aspiration pneumonia and died

Discussion

Computerized Tomographic Angiography is rapidly gaining a role as a primary tool for the diagnosis of vascular disease. The advancement of 16-slice MDCT in conjunction with spiral CT allows a craniocervical CTA to be performed in less than 10 minutes. From the patient perspective, the diagnostic study is identical to a routine CT of the neck and head. Furthermore, claustrophobia or metallic implants are not contraindications to a CTA. Increasingly, single center trials are demonstrating a high sensitivity and specificity of CTA compared to DSA for multiple vascular beds including, carotid arteries, renal arteries, and lower extremity arteries. The use of 16-detector CT scanners has increased the resolution for arteries as small as 2 mm that previously were equivocally evaluated by the earlier 4-detector or single detector spiral CT scan. Several vendors have introduced scanners with 32, 40 or more detectors and formal evaluation is now underway. Most CTA studies can be performed with 100-150 cc or less of iodine-based contrast. In patients with iodine allergy, premedications are effective in reducing allergic reactions. In patients with renal dysfunction, periprocedural hydration, iso-osmolar contrast and N-acetylcysteine can be employed to decrease the incidence of azotemia. In our experience, diagnostic studies can be achieved with less than 100 cc of contrast if needed. Several studies have demonstrated CTA to be associated with high sensitivity and specificity in identifying significant carotid disease. Near occlusions or 'string sign’ is also accurately identified by CTA when compared to DSA. In the reported case study, CTA clearly identified an occluded R ICA and a L ICA with approximately 60% stenosis. This case report represents the first report of basilar artery stenosis correctly identified on CTA. The long, smooth narrowing of the basilar artery in this patient may be related to the patient’s prior laryngeal irradiation; however, the patient clearly had multiple atherosclerotic risk factors as well, including hypertension, diabetes and tobacco use. The images demonstrating the stenotic origin of the aberrant vertebral artery origin also demonstrate the utility of CTA for the evaluation of suspected vertebrobasilar insufficiency. In clinical practice, many patients undergo carotid duplex as a diagnostic tests; however, CTA imaging of the vertebral arteries routinely includes visualization of the carotid arteries, which may abrogate the need for carotid ultrasound in many patients. This case study demonstrates the utility of MDCT as a primary tool for evaluation of extracranial and intracranial vascular disease. It is anticipated that as additional detectors and software algorithms advance, image resolution will improve and study time will decrease.

The author can be contacted at: Cgoldman@ochsner.org Dr. Goldman has nothing to disclose.