T1 post-gad T1 post-gad R vert angio Towne projection

Diagnosis: Left AICA aneurysm

Aneurysms involving the vertebral basilar system make up 5-10% of all intracranial aneurysms. Those involving the peripheral aspect the anterior inferior cerebellar artery are extremely rare. Symptoms that have been reported due to AICA aneurysm include subarachnoid hemorrhage and mass effect upon the 7th and 8th cranial nerve complex resulting in vertigo, tinnitus, and deafness. Nearly all of the reported AICA aneurysms originated from arterial loops near the acoustic meatus. Erosion of the internal auditory canal has also been reported.

If the angiogram were not available, the differential diagnosis of this lesion would also include hemangioma, meningioma, ependymoma and schwannoma. Although the lesion does lack a dural tail, which would suggest meningioma and it seems somewhat removed from the internal auditory canal which goes heavily against schwannoma. Other remote considerations may include a metastasis or an exophytic astrocytoma. This lesion has a bright rim on T1 pre gad which suggests subacute thrombus in the periphery. This is born out by the angiogram which showed a small lesion measuring approximately 3 mm in diameter. The MRA is somewhat misleading since it was performed after the administration of gadolinium. Most of the subtle signal which is seen on the MRA in the vicinity of the lesion is probably due to the presence of the thrombus whose T1 has been additionally shortened by the administration of gadolinium. The surgical report states that the aneurysm was either a focal fusiform type or a broad based saccular type which was approximately 1 cm in diameter. The aneurysm was seen to be compressing the 7th and 8th cranial nerve complex inferiorly. Related Cases

Uede T, Matsumura S, Ohtaki M, et al. Aneurysm of the anterior inferior cerebellar artery at the internal auditory meatus: report of two cases. No Shinkei Geka, Spe 1986; 14(10): p1263-8.

Dalley RW, Robertson WD, Nugent RA, et al. Computed tomography of anterior inferior cerebellar artery aneurysm mimicking an acoustic neuroma. J Comput Assist Tomogr, Sep-Oct 1986; 10(5):p881-4.

Fukuya T, Kishikawa T, Ikeda J, et al. Aneurysms of the peripheral portion of the anterior inferior cerebellar artery; report of two cases. Neuroradiology, 1987; 29(5):p493-6.

Rinehart R, Harre RG, Roski RA, et al. Aneurysm of the anterior inferior cerebellar artery producing hearing loss. Ann Otol Rhinol Laryngol, Aug 1992; 101(8):p705-6.

Acoustic schwannoma AICA aneurysm