Isolated abducens nerve palsy caused by contralateral vertebral artery dolichoectasia.

hematological investigations were all within normal limits. Magnetic resonance (MR) imaging and MR angiography of the brain and orbit demonstrated compression of the right abducens nerve superiorly and laterally by dolichoectatic left VA. No other abnormal signals were seen in brainstem [Figure 1]. Owing to the fact that the right abducens nerve palsy was mild and the patient showed no diplopia in the primary position, no treatment was administered. Six months after the first examination, no changes in neurological findings had been detected. The dolichoectatic VA is the site of marked pathological elongation, widening, and tortuosity. The etiology of dolichoectasia is unclear. Severe arteriosclerotic changes associated with hypertension had been reported as a cause of dolichoectasia of vertebrobasilar system. On the other hand, because of its occurrence in some young people, several congenital factors may contribute to its development. [5] When VA is dolichoectatic, it deviates from its course ventral to the brainstem and may compress the cranial nerves, most frequently as they emerge from the brain stem (root entry zone). The facial and trigeminal nerves are the mostly affected ones. In addition DVA can produce ischemic stroke, transient ischemic attacks, and intracerebral hemorrhage. The abducens nerve is one of the longest nerves in its peripheral course that predisposes this cranial nerve to involvement at all levels, from the brain stem and base of the skull, through the petrous tip and cavernous sinus, to the superior orbital fissure and orbit. Because of this, the sixth nerve is more liable to injury by some conditions such as trauma or inflammatory lesions. Abducens nerve palsy usually results from brainstem ischemia, hemorrhage, infiltration of tumor or vascular compression, and is always associated with facial weakness and pyramidal signs in the central lesions. After emerging from the brainstem, occasionally, the abducens nerve may be compressed by vascular structures such as an enlarged ective observation or surgical evacuation of the clot can be the treatment options.