The term dolichoectasia means elongation and distention. In the vertebrobasilar system this term is appropriately used if the basilar artery courses lateral to the clivus or dorsum sellae or if the bifurcation of the basilar artery occurs above the plane of the suprasellar cisterns. Ectasia implies a basilar artery with a diameter greater than 4.5 mm. The pathogenesis is probably related to marked thinning of the internal elastic lamina and media, most likely a consequence of prolonged systemic arterial hypertension.
The clinical relevance of vertebrobasilar dolichoectasia (VBD) is related to the severity of the elongation and ectasia. Symptoms are related to direct cranial nerve compression, ischemic effects on the brain stem and cerebellar hemispheres as well as symptoms related to hydrocephalus. Direct cranial nerve compression can lead to isolated cranial nerve dysfunction, usually associated with a normal-sized basilar artery that is tortuous and elongated. Isolated cranial nerve dysfunction most commonly involves the VII cranial nerve (hemifacial spasm or paresis) and the V cranial nerve (trigeminal neuralgia). Multiple cranial nerve dysfunction is far more likely to occur if there is dilation (ectasia) associated with a tortuous and elongated basilar artery. Cranial nerves affected in descending order of frequency include: VII, V, III, VIII, and VI. Trigeminal neuralgia associated with hemifacial spasm is one commonly encountered combination.
Ischemia may be caused secondary to direct mass effect and/or hemodynamic changes from marked stasis of flow (more common with larger basilar artery diameters). These patients present with nystagmus, vertigo, dysarthria, ataxia, hemiparesis and/or seizures. They frequently have a rapidly progressive downhill clinical course. Additionally, patients with the largest diameter basilar arteries have an increased incidence of complications from conventional angiography (especially with diameters greater than 1 cm). In the appropriate clinical setting, evaluation of VBD may be performed with CT or MR, usually to the exclusion of angiography.
Film .4 is a series of MR images of a 71-year-old male with bilateral VI and mild left V cranial nerve dysfunction. Additionally, he has left-sided hyperreflexia and urinary and stool urgency. Again noted is severe VBD with the distal basilar artery compressing the hypothalamus and right internal capsule (Film .4 - scan 6) with its terminal bifurcation near the level of the foramen of Monro (Film .4 - scan 3)! Also note mild compression of the medulla by the right vertebral artery, which is also ectatic.
Film .5 is an AP image from a left vertebral angiogram on a 69-year-old male with a right III nerve palsy. What is the cause of this patient's III nerve palsy? Note the deviation of the basilar artery to the right and then back to the left with rotation of the terminal portion such that the proximal right superior cerebellar (SCA) and posterior cerebral (PCA) arteries course cephalad instead of to the right. Recall that the third cranial nerve exits the midbrain and crosses the interpeduncular cistern between the PCA and SCA. In this case, the rotated distal basilar artery has caused the right PCA and SCA to trap and stretch the III cranial nerve, leading to the palsy.
Film .6 is a contrast-enhanced CT scan of a 65-year-old male with dementia. The basilar artery demonstrates anterior deviation and high termination. The basilar tip indents the floor of the third ventricle and appears to lie within it on scan 6. This can be associated with hydrocephalus with obstruction anterior, near the foramen of Monro, or posterior, simulating aqueduct obstruction. The hydrocephalus is often associated with anatomically patent cerebrospinal fluid pathways and normal mean CSF pressures. True obstructive hydrocephalus has also been reported.