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Neuroradiology Case of the Week

Case 76

Ravinder Sidhu MD, Leena Ketonen, MD, PhD,
and P-L Westesson MD, PhD, DDS

Clinical Presentation: A 69-year-old male presented with acute seizure.

Radiological Findings:  Non-contrast enhanced head CT showed an ill-defined hypodense area involving the cerebellar hemispheres, part of the brain stem, and occipital lobes. There was mild compression over the fourth ventricle from right side (Fig.1) The basilar artery appeared hyperdense suggestive of acute thrombus within it (Fig. 2).

Diagnosis: Acute basilar artery thrombosis

Discussion:  Thrombosis of the basilar artery is an uncommon but potentially fatal condition characterized by sudden onset of neurological dysfunction including hemi-or-quadriparesis, deficits of lower and upper cranial nerves, respiratory difficulty, altered sensorium, vertigo, and ataxia [1].
     The most common causes of thrombosis of the basilar artery include embolism (secondary to bacterial endocarditis and rheumatic or congenital heart disease), atherosclerosis, vascular malformations involving the base of skull, and vasculitides associated with tuberculosis, and/or fungal infection [2].
     Radiologically, the diagnosis of ischemic cerebral infarction by computed tomography is usually not possible for 12-24 hours after the event. However, there are very subtle changes such as reduced attenuation and slight mass effect. A sign of cerebral infarction that may be present shortly after the ictus is increased density in a major cerebral artery known as “hyperdense artery sign” [1]. This may presumably be caused by the presence of thrombus. MR imaging may show intermediate signal intensity on T1 and low signal intensity on T2-weighted images. This may be due to deoxyhemoglobin within fresh intraluminal thrombus. MR angiography may show lack of flow within the thrombosed artery [3]. MR imaging along with MR angiography is the modality of choice whenever there is strong clinical suspicion of basilar artery thrombosis since artifacts in posterior fossa seen in computed tomography may hinder in picking up subtle changes, thus causing delay in diagnosis and treatment.

References:

1. Schuknecht B, Ratzka M, Hofmann E. The “dense artery sign”- major cerebral artery thromboembolism demonstrated by computed tomography. Neuroradiology 1990; 32:98-103.
2. Castillo M, Falcone S, Naidich TP, Bowen B, Quencer RM. Imaging in acute basilar artery thrombosis. Neuroradiology 1994; 36:426-429.
3. Schwaighofer BW, Klein MV, Lyden PD, Hesselink JR. MR imaging of vertebrobasilar vascular disease. J Comput Assist Tomogra. 1990; 14:895-905.