Name : Hamidreza
Affiliation : ----------------
Academic Degree: ----------------
Resident : Farhad Niaghi
Gender : Male
Age : 55
Head & Neck Imaging
55 year old man with vertigo and headache
Imaging Procedures and Findings
there is an extra-axial hyperdense mass in prepontine cistern that replaces basilar artery. The mass is well defined but has heterogenous internal signal in T1WI and T2WI with an enhancing portion in T1+gad. Tourtous ectasia and elongation and high termination of basilar artery are noted.
Cerebral aneurysms may be saccular, fusiform, or dissecting. Fusiform aneurysms can be regarded as an extreme form of focal ectasia in arteriosclerotic disease. Intracranial aneurysms can also develop following an arterial dissection. However the majority are saccular aneurysms, which are usually round or lobulated and arise from arterial bifurcations. Giant aneurysms by definition measure over 25 mm in diameter and account for approximately 5 percent of all cerebral aneurysms. They often contain layers of organized thrombus. Aneurysms tend to present with SAH or mass effect on adjacent structures, most commonly a posterior communicating artery aneurysm causing a third nerve palsy. Around 90 percent of intracranial aneurysms arise from the carotid circulation, the remaining 10 percent from vertebral or basilar arteries. The anterior and posterior communicating arteries give rise to approximately one-third each of all intracranial aneurysms, with another 20 percent from middle cerebral arteries and 5 percent from the basilar termination. The remainder arises from other vessel origins and bifurcations.A clot in the septum pellucidum, possibly extending into one or other frontal lobe, is virtually diagnostic of an aneurysm of the anterior communicating artery. Aneurysms of the distal anterior cerebral artery related to pericallosal branches are less common. Aneurysms of the MCA bleed into the Sylvian fissure, sometimes with a clot in the temporal lobe. Aneurysms of the posterior communicating artery (which arise from the internal carotid artery at the origin of this vessel) are a frequent cause of SAH but can also present with isolated third nerve palsy due to pulsatile pressure on the nerve. Other relatively common sites of aneurysms of the internal carotid artery are the origin of the ophthalmic and anterior choroidal arteries and its terminal bifurcation.Aneurysms of the posterior circulation are commonly located at the basilar arterybifurcation and if they rupture blood may be seen in the interpeduncular fossa, brainstem or thalamus; prognosis is frequently poor. The second commonest site in the posterior circulation is at the origin of one of the posterior inferior cerebellar arteries. They often hemorrhage into the ventricular system via thefourth ventricle and downwards into the spinal subarachnoid space. Larger aneurysms are shown on CT and MRI. On CT they appear as rounded enhancing lesions. Giant aneurysms have an enhancing lumen and a wall of variable thickness that often contains laminated thrombus and may be calcified. On spin-echo MRI sequences a patent aneurysm appears as an area of flow void. Areas of increased signal intensity within the aneurysm may representmural thrombus or turbulent, slow flow
Basilar artery aneurysm with internal clot. Dolicoectasia of basilar artery.
Grainger & Allison's Diagnostic Radiology, 5th ed