Chronic Recanalization of Dissection of the Distal Anterior Cerebral Artery: Case Report and Review of the Literature

The natural history of atraumatic idiopathic dissection of the distal anterior cerebral artery is still unclear. We present a 38-year-old man who had dissection of the left A2 segment of this vessel associated with subintimal hematoma and infarction. Because of complete stroke in acute stage, he did not undergo surgery. About three months later, administration of aspirin (100 mg/day) was started. At nine months, magnetic resonance angiography revealed complete recanalization of the A2 dissection. To assess the outcome of dissection, we should observe the patient for at least one year.


Introduction
Atraumatic intracranial dissecting aneurysm mainly occurs in the vertebrobasilar or internal carotid arteries [1]. Although reports about dissecting aneurysms of the distal anterior cerebral artery have been gradually increasing, especially in Japan, the clinical course and treatment of this lesion are still unclear. We report an unusual case of dissection of the distal anterior cerebral artery that showed angiographic recovery by 9 months after the onset with antiplatelet therapy alone. We also review the relevant literature.

Case Report
While urinating, a 38-year-old man suffered from the sudden onset of severe headache, difficulty speaking, and right hemiparesis (the lower extremity was more severely affected). He was taken to a local hospital by ambulance. Computed tomography (CT) showed thin subarachnoid hemorrhage (SAH) on the left side of the interhemispheric fissure (Fisher's group 2 [2]) (Figure 1(a)). Magnetic resonance imaging (MRI) revealed left frontal lobe infarction (Figure 1(b)), and cerebral angiography indicated stenosis (string sign) of the distal left anterior cerebral artery (A 2 segment) (Figure 1(c)). A tentative diagnosis of idiopathic SAH with early spasm of the left A 2 segment was made. After two weeks of medical treatment, repeat cerebral angiography showed no source of SAH and persistent A 2 stenosis. His speech improved, but right hemiparesis persisted. After transfer to a rehabilitation hospital, it was decided to reexamine his condition and he was admitted to our hospital.
On admission, he had right hemiparesis (4/5 for the upper limb on manual muscle testing and 2/5 for the lower limb). MRI showed medial left frontal lobe infarction with poor perfusion of the left A 2 segment (Figure 2(a)). Angiography also revealed severe stenosis (string sign) of the left A 2 segment (Figure 2(b)). Because the string sign without pear appearance (stenosis without dilation) warranted the diagnosis of the dissecting aneurysm by some articles [3][4][5], the final diagnosis was dissection of the left A 2 segment of the anterior cerebral artery. Because his clinical status was stable, he was returned to the rehabilitation hospital.
Two months later, he was reviewed at our outpatient clinic. His right upper limb was recovered but his right lower limb was 3+ ∼ 4/5 on manual muscle testing. Because the left distal anterior cerebral artery did not recanalize at that time, aspirin (100 mg/day) was commenced. Six months later, magnetic resonance angiography (MRA) showed recanalization of the left A 2 segment (Figure 2(c)). Because repeat MRA also showed patency of the left A 2 segment one year later, aspirin therapy was ceased. There have been no new neurological problems during followup.
The combined hemorrhage and infarction group comprised five patients (including ours) with SAH and infarction [10,11,38,39], as well as one patient with ICH and infarction who did not undergo surgery [40]. A 3 -A 3 bypass and trapping was done in one patient with SAH and infarction [39], wrapping was performed in one [38], and three patients (including ours) were managed conservatively [10,11]. Among the last three patients, recanalization of the dissection was confirmed in two, with one receiving no antiplatelet or anticoagulant therapy [10] and the other being our patient. The period from the onset until angiographic confirmation of recanalization was 18 months and 9 months, respectively.
Although anticoagulation and/or antiplatelet medication may be a widely accepted conservative management for intracranial arterial dissection with purely ischemic symp-tom, two patients with infarction onset died of adverse drug reactions. One was administered sodium ozagrel (80 mg/day) for 12 days after infarction, but severe SAH occurred on the 12th day [13]. Another patient received antithrombin therapy in the acute stage, followed by an antiplatelet drug. On day 21 after the onset, he suffered from severe ICH [6]. On the other hand, 11 patients were safely administered urokinase [16], ozagrel [11,[18][19][20], heparin [21,22], argatroban [12], ticlopidine [14], aspirin [12,14,21], or antiplatelet drugs [17] during the acute stage. Three of these 11 patients achieved angiographic cure [14,16,17]. These results suggest that we must pay close attention when using these drugs in the acute stage of distal anterior cerebral artery dissection.

Conclusion
We reported a patient with dissection of the anterior cerebral artery (A 2 segment) who showed recanalization after 9 months with only aspirin therapy. It may be important to monitor such patients for at least one year to determine the clinical outcome.