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 8 th 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

TI WI T2 WI Proton WI 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

 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