Object: Noninvasive neuroimaging techniques are increasingly identifying unruptured intracranial arterial dissections (IADs) at examination for headache or ischemic symptoms. Approximately 3% of cases of aneurysmal subarachnoid hemorrhage (SAH) are caused by IADs in Japan, but the natural history of unruptured IADs is not known.
Methods: Clinical data obtained in 190 patients with 206 IADs were retrospectively analyzed on the basis of long-time follow-up of geometry and clinical event. The IADs were divided into an unruptured group and SAH group depending on the patient's clinical status at the initial diagnosis. Day 0 was defined as the day preceding diagnosis of IAD-that is, the day of symptom onset. This was retrospectively determined from the clinical history.
Results: The 206 IADs included 98 unruptured lesions and 108 SAH. In both groups, the vertebral artery was the most frequent site. In the unruptured group, 93 IADs were followed for a mean of 3.44 years. The mean interval between symptom onset (Day 0) and neuroimaging diagnosis was 9.8 days. Subsequent geometry change was seen in 78 (83.9%) of 93 IADs. Major change was almost completed within 2 months, and complete normalization was seen on neuroimaging in 17 (18.3%) of 93 IADs, with the earliest on Day 15. Rupture of the IAD in the unruptured group occurred in only 1 patient on Day 11. In the SAH group, 84 of the 108 patients complained of preceding headache before onset of SAH. In 81 (96.4%) of the 84 patients, SAH occurred on Day 0-3 with the latest on Day 11. In all patients in the unruptured and SAH groups, the latest day of SAH from the onset of preceding headache was Day 11.
Conclusions: Most IADs causing SAH bleed within a few days of occurrence. Most IADs that are unruptured already have little risk for bleeding at diagnosis because of the repair process. Intracranial arterial dissections may be much more common than previously thought, and the majority may occur and heal without symptom manifestation.