Giant PICA Aneurysm

Kathleen A. Sorensen, MD; Georgianne M. Snowden, MD


Appl Radiol. 2007;36(11):66-70. 

In This Article


A 43-year-old woman presented to an outside hospital with a 10-month history of progressive headaches, nausea, and vomiting. On physical examination, mild bilateral nystagmus on lateral gaze and rotatory nystagmus were present. Mild ataxia was present.

Magnetic resonance imaging (MRI) of the brain obtained at the outside hospital reported a large posterior fossa tumor within the fourth ventricle as well as obstructive hydrocephalus. The patient underwent a second MRI after being transferred to another hospital for neurosurgical removal of the tumor. The differential considerations for both studies included ependymoma, subependymoma, neurocytoma, giant cell astrocytoma, and metastasis. The patient was scheduled for a craniotomy and surgical excision. In the operating room, the patient was noted to have a large "pulsatile mass," which was determined to be an aneurysm. The aneurysm was successfully clipped. Neither examination was reviewed by a neuroradiologist until an intraoperative consult was given, at which time a correct diagnosis of giant posterior-inferior cerebellar artery (PICA) aneurysm was made.

Giant PICA aneurysm

MRI of the brain with and without gadolinium enhancement showed a 3.4 × 2.6 × 3.0-cm lesion situated within the region of the fourth ventricle. It had a concentric multilaminated appearance (Figure 1). A flow void originating from the right PICA was present on midline sagittal T1-weighted images (Figure 2).  Gadolinium injection revealed central enhancement of the mass (Figure 3) with enhancement of the PICA that was seen directly feeding into it (Figure 4). Pulsation ghosting artifact was also present (Figure 5).

A T1-weighted sagittal noncontrast MR image shows a large multilaminated fourth ventricle mass.

In this T1-weighted midline sagittal MR image without contrast, a flow void can be seen at the anterior edge of this mass, which represents the distal right posteriorinferior cerebellar artery.

A T1-weighted 3-dimensional axial gadoliniumenhanced MR image reveals the enhancement of the central portion of the mass.

The posterior-inferior cerebellar artery is seen to be directly feeding into the mass on this T1-weighted coronal MR image after gadolinium enhancement.

A pulsation artifact, known as phase ghosting, indicates that flowing blood is present within the mass, which suggests that the mass could be an aneurysm.


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