The case is presented of a 37-year-old man (Lee Stein) with spontaneous thrombosis of a 10-mm left posterior communicating artery aneurysm, following presumed subarachnoid hemorrhage with negative angiography. Sequential magnetic resonance angiography and magnetic resonance source imaging (at 2 weeks, 3 months, 2 years, and 2 years, 5 months) showed progressive shrinkage and disappearance of the aneurysm.

A 37-year-old man complained of a dull ache in the left temporal and posterior ocular area initially felt to represent tension-type headache. He had a history of similar episodes 16 years earlier while under stress in law school. The next day, the headache became incapacitating, to the extent that the patient locked himself in a dark quiet room for 3 days.

Seven days later, the patient returned to the clinic complaining of less severe, but persistent headache. He was seen by a neurologist and referred for MRI. Neurologic exam was negative at that time. MRI performed 3 days later showed a 10-mm left posterior communicating artery aneurysm with bright signal on T1 weighted precontrast images, suggesting either slow flow or thrombosis. MRA was not available at that time.

A three-vessel cerebral angiogram (figure at right) with cut film and digital subtraction was performed, including multiple oblique magnification views. No evidence of a cerebral aneurysm, nor of vasospasm, was seen. The patient elected to have the aneurysm followed by MRA, and was referred to a sister institution for baseline study. A three-dimensional (3-D) phase contrast MRA showed no evidence of flow within an aneurysm. Three-dimensional time-of-flight MRA performed at the same time did show bright signal in the aneurysm, consistent with recent thrombosis.

Repeat MRA 3 months later showed the left posterior communicating artery aneurysm to have reduced in size to 6 mm, with no evidence of flow within the aneurysm. The 3-D time-of-flight MRA source image which had previously shown bright signal within the aneurysm now showed dark signal consistent with thrombus evolution.

Repeat MRA 2 years after the initial presentation showed no evidence of an aneurysm. T1 weighted spin-echo MRI showed a tiny residual nubbin adjacent to the left posterior communicating artery origin, with no evidence of a flow void. Magnetic source imaging (MSI) performed with magnetoencephalography showed diffuse spontaneous slow-wave activity [12,13] over the left hemisphere, indicative of possible cortical dysfunction.

Repeat MRA at 2 years and 5 months after the ictus showed no evidence of an aneurysm on 3-D time-of-flight nor on 3-D phase-contrast MRA, and showed further disappearance of the aneurysm on the source images. The patient has continued to do well 3 years and 2 months after the aneurysm was initially discovered, but he does have occasional mild left-sided headaches. He does not wish to undergo