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By: Nour-Eldin A Mohammed Referrence:Stephan Chapman 2003 Extra-axial area lateral to the prepontine cistern containing CSF, arachnoid tissue, cranial nerves and their associated vessels. Borders Medial: lateral surface of the brainstem Lateral : petrous bone Superior : middle cerebellar peduncle & cerebellum Inferior : arachnoid tissue of lower cranial nerves Posterior : cerbellar peduncle 1. Vestibular Schwannoma (acoustic neuroma). Most Common Cause 2. Meningioma 3. Epidermoid cyst 4. Trigeminal neuroma 5. Vertebrobasilar system aneurysm 6. Metastases 7. Skull base/temporal bone tumours:eg, glomus tumors,metastases,cholesterol granuloma 8. Skull base infection:osteomyelitis of the petrous apex (Gradengo’s syndrome) , Malignant otitis externa Comprises 60-92% of CPA lesions Involve the vestibular division of the 8th cranial nerve Features of Acoustic Neuroma: 1. Centered over the petrous bone 2. Acute angle with the petrous bone 3. Extension into the internal auditory canal 4. Homogenous enhacement 5. No dural tail 6. No calcifications Second most common CPA lesion 3-7 % Arise from cap cells near arachnoid villi which are more prominent near cranial nerve foramina and venous sinuses. Usually arise from posterior surface of the petrous bone and usually do not extend into IAC Features of Meningioma: 1. Broad base over the petrous bone 2. Homogenous signal 3. A small toungue extension into the internal auditory canal without widening it 4. Homogenous enhacement 5. dural tail 6. Calcifications , psammoma bodies 7. Hyperostosis Accounts for 2-6 % of CPA masses Congenital lesions that present in adulthood Rests of ectodermal tissue containing stratified squamous lining and keratin May arise within the temporal bone or in the CPA Features of Epidermoid: 1. Low density Cyst with lobulated margin 2. CSF like signal (with high signal in diffusion,flair and proton seq 3. May exert extensive mass effect 4. Also occur parasellar and rarely itra diploic T2 WI TI WI Proton WI Similar to vestibular neuoma but arises from the trigeminal nerve 1. Vertebrobasilar dolichoectasia: Enlongation and dilitation of the vertebrobasilar artery. Symptomas : Facial spasm, trigeminal neuralgia 2. AICA loop May loop over, under, or between CN VII & CN VIII. Symptoms - vertigo 3. Giant Aneurysms 4. Hemangioma 5. Paragangliomas (may extend to CPA) Glomus Jugulare Glomus Tympanicum Anterior inferior cerebellar artery Giant aneurysm