giovedì 1 giugno 2006
Giant paraclinoid ICA aneurysm
Noncontrast CT: Peripheral calcifications. High density lumen (Figure 1) representing nonthombosed blood in the aneurysm lumen.
T1-weighted MRI (Figure 2), T2-weighted MRI (Figure 3): Hemorrhage of varying ages in aneurysm wall including T1 bright, T2 bright crescent-shaped hyperacute periluminal blood in wall (Figure 2 and Figure 3) representing methemoglobin. Pulsation artifact due to blood flow in patent lumen (Figure 2 and Figure 3).
Diagnosis: Giant paraclinoid ICA aneurysm
Giant cerebral aneurysms, defined as cerebral aneurysms greater than 2.5 cm in size, typically occur in the fifth to seventh decade with slight female preponderance. These aneurysms commonly present with symptoms related to subarachnoid hemorrhage – severe headache, nausea, vomiting, and loss of consciousness – or progressive neurologic dysfunction due to mass effect. Patients may also present with signs and symptoms caused by cerebral ischemia secondary to dislodged intramural thrombus.
Partially thrombosed giant aneurysms have a characteristic MRI appearance due to its dual component nature (thrombosed portion with layering clot, and patent portion with flowing blood). Typically, they appear as well-circumscribed mass lesions with mixed signal intensities and varying ages of clot in the thrombosed portion of the aneurysm. The patent portion will demonstrate evidence of flow including signal void, enhancement, and pulsation artifact.
Giant aneurysms are classified as saccular, fusiform, or serpentine giant types:
1) Saccular aneurysms are believed to arise from smaller saccular aneurysms. Proposed mechanisms include turbulent flow, which induces endothelial damage from turbulent flow that induces recurrent scarring, and mural thrombus formation. Another theory is that there are recurrent hemorrhages in the aneurysm wall, causing expansion.
2) Fusiform aneurysms develop from artherosclerotic degeneration of the arterial wall and involve longer segments of intracranial arteries.
3) Serpentine aneurysms are a type of fusiform aneurysm with irregular, tortuous lumen. Development is not well understood.
Treatment options are varied and are dependent on each individual case, including direct clipping of the neck (particularly for narrow-necked saccular aneurysms), surgical ligation, endovascular treatment, and surgical bypass