1. Usual and unusual lesions of the cerebellopontine angle Juan P. Ovalle R. MD. Diagnostic Neuroradiology Cedicaf Colombia #2613

2. Disclosures Nothing to disclose

3. Purposes Give an easy approach to classify CPA lesions depending if there is enhancement or not after contrast material. To illustrate the main features on MR of usual and unusual cerebellopontine angle (CPA) lesions with MR techniques, basic sequences T1WI, T2WI, FAT-SAT, gadolinium enhancement and DWI.

4. Introduction The CPA cistern is a subarachnoid space containing cranial nerves and vessels bathed in CSF. It is centered by the internal auditory canal (IAC) and extends caudally from the Vth cranial nerve to the IX-X-XIth cranial nerve complex. Vestibular schwannomas and meningiomas account approximately 90-95% of all CPA lesions, but we can see unusual lesions such as epidermoid cyst, aneurysm, metastasis, intra-axial lesion involving the CPA angle like glioma, hemangioblastoma, papilloma, ependymoma, lymphoma and skull base lesions such as paraganglioma or endolymphatic sac tumors.

5. Approach CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1

6. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Vestibular schwannoma Trigeminal schwannoma Facial nerve schwannoma Meningioma Metastasis Aneurysm

7. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lymphoma Glioma Metastasis Hemangioblastoma Medulloblastoma Papilloma Ependymoma

8. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Paraganglioma Chondromatous tumors Chordoma Endolymphatic sac tumor

9. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lipoma Neuroenteric cyst Cholesterol granuloma

10. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Epidermoid cyst Arachnoid cyst

11. Vestibular schwannoma The most frequent tumor in the CPA, accounting for 70% to 80% of all CPA mass. Benign tumor arising from vestibular portion of CN8 at glial Schwann cell junction, rare in cochlear portion CN8. They smoothly erode the posterior edge of the porus acusticus and may give rise to a round or oval component in the CPA cistern, thus giving the typical “ice cream on cone” pattern. On MR, they show T1 isointensity and T2 hyperintensity and enhance strongly after gadolinium injection. On DWI is isointense to the parenchyma. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Vestibular schwannoma Trigeminal schwannoma Facial nerve schwannoma Meningioma Metastasis Aneurysm

12. Vestibular schwannoma T1WIT1WI+G T2 steady state DWI CPA mass with “ice cone cream” shape, enhancing and eroding the porus acusticus CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Vestibular schwannoma Trigeminal schwannoma Facial nerve schwannoma Meningioma Metastasis Aneurysm

13. Vestibular schwannoma T1WI T1WI+G T2WI GRE DWI Left CPA mass with high signal on T1WI due to hemorrhage, low signal on GRE, mass effect and edema on the middle cerebellar peduncle CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Vestibular schwannoma Trigeminal schwannoma Facial nerve schwannoma Meningioma Metastasis Aneurysm

14. Cystic Vestibular schwannoma T1WI+G T2WI T1WI Solid-cystic right CPA mass enhancing with mass effect CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Vestibular schwannoma Trigeminal schwannoma Facial nerve schwannoma Meningioma Metastasis Aneurysm

15. Trigeminal schwannoma Non vestibular schwannomas are rarely present in the CPA. Trigeminal schwannoma is the most frequent lesion among non-vestibular schwannomas. It is located cephalic to vestibular schwannoma, has an anterior-posterior direction in the CPA cistern and may extend into the Meckel´s cave and along trigeminal branches. Is a benign tumor and may be associate to neurofibromatosis. Its size could be small to giant and a dumbbell shape due to constriction at porus trigeminus or skull base foramen. On MR T1 iso or hypointensity, on T2 hyperintensity, and may have variable enhancement, cystic formation is common. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Vestibular schwannoma Trigeminal schwannoma Facial nerve schwannoma Meningioma Metastasis Aneurysm

16. Trigeminal schwannoma T2WI T1WI+G T1WI T1WI+G DWI Solid and cystic left Meckel´s cave lesion expanding with mass effect on the left medial temporal lobe CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Vestibular schwannoma Trigeminal schwannoma Facial nerve schwannoma Meningioma Metastasis Aneurysm

17. Meningioma Is the most common intracranial extra-axial tumor in adults, but is the second most frequent lesion in the CPA after VS representing 10-15% of all tumors in this location. They are usually located at the posterior aspect of the temporal bone or at the premeatal area, without enlarging porus acoustic. There is frequent adjacent bone reaction including hyperostosis. MRI clearly depicts a broad-based dural hemispheric, attached to the petrous dura or the inferior aspect of the tentorium. Isointense on T1WI and T2WI and strongly enhance after contrast. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Vestibular schwannoma Trigeminal schwannoma Facial nerve schwannoma Meningioma Metastasis Aneurysm

18. Meningioma T2WIT1WIDWI T1WI+G Right extra-axial CPA mass well define broad based with enhancement, displacement of the middle cerebellar peduncle, there is not enlarging of IAC CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Vestibular schwannoma Trigeminal schwannoma Facial nerve schwannoma Meningioma Metastasis Aneurysm

19. Vertebrobasilar aneurysm and dolichoectasia can lead to cranial nerves or brain stem compression when are involving the CPA cistern. At MR aneurysm without significant internal thrombus have obvious flow voids on all spin echo sequences, but demonstrate iso to high signal intensities and variable patterns of gadolinium uptake on T1WI when intraluminal thrombus is present. Aneurysm of PICA, AICA, vertebral artery or the basilar artery itself could be depicted on MRA. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Vestibular schwannoma Trigeminal schwannoma Facial nerve schwannoma Meningioma Metastasis Aneurysm

20. Vertebrobasilar aneurysm on the left CPA displacing the cerebellar hemisphere and pons to the right, flow void on T2WI and enhancing after contrast T1WI T2WI T1WI+G CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Vestibular schwannoma Trigeminal schwannoma Facial nerve schwannoma Meningioma Metastasis Aneurysm

21. Intra-axial and intraventricular lesions Anatomic landmarks are not always reliably depicted in the posterior fossa, and the intra- or extra-axial location of a lesion is not always certain, especially when the cistern itself is no longer depicted. Extensive peritumoral edema surrounding and enhancing lesion, centered on a significant mass effect obliterating the CPA cistern is very unlikely in a benign extra-axial tumor. In this circumstance, an intra-axial tumor such as a glioma, lymphoma or a metastasis should be suspected. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lymphoma Glioma Metastasis Hemangioblastoma Medulloblastoma Papilloma Ependymoma

22. Intra-axial and intraventricular lesions Glial tumors of the brain stem, especially pilocytic astrocytomas in young adults, can manifest as asymmetric expansion of the brain stem that can be pedunculated or exophytic, invading the CPA. Glial tumor invading CPA angle do not have a specific imaging features in this location, they appear with T2 hyperintensity, T1 hypointensity and variable enhancement depending on the glioma grade, they are usually surrounded by adjacent edema and DWI depends of the cellularity. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lymphoma Glioma Metastasis Hemangioblastoma Medulloblastoma Papilloma Ependymoma

23. Glioma CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lymphoma Glioma Metastasis Hemangioblastoma Medulloblastoma Papilloma Ependymoma T1WI+G T2WI DWI T1WI Intra-axial pontine mass, expansive, engulfing the basilar artery, involving the CPA angles and displacement of IV ventricle and IAC structures

24. Intra-axial and intraventricular lesions Hemangioblastomas are benign vascular intra-axial tumors preferentially located in the cerebellar hemispheres, with a possible extention into the CPA. They are sporadic in the majority of cases, but could be a manifestation of Von Hipple-Lindau disease in 25%. Usually present as well-circumscribed masses with smooth margins, either entirely solid (40%) or cystic, with hypervascular enhancing mural nodule (60%), hypointensity on T1 and hyperintense on T2 WI, there is strongly enhancement after contrast. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lymphoma Glioma Metastasis Hemangioblastoma Medulloblastoma Papilloma Ependymoma

25. Hemangioblastoma CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lymphoma Glioma Metastasis Hemangioblastoma Medulloblastoma Papilloma Ependymoma T1WI+G T2WI DWI FLAIR T1WI Intra-axial cystic mass lesion on the right cerebellar hemisphere, with an enhancing solid nodule and perilesional edema

26. Intra-axial and intraventricular lesions Medulloblastomas are primary neuroepithelial tumors that occur midline in the posterior fossa of children. Differences in the imaging characteristics of adult medulloblastomas could be involvement of lateral cerebellar hemispheres with a possible extra-axial appearance, or even a primary extra-axial location mimicking either a meningioma or a vestibular schwannoma due to an extent into the internal auditory canal. On MR medulloblastomas are isointense or hypointense on T1 and T2WI and enhance moderately after contrast. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lymphoma Glioma Metastasis Hemangioblastoma Medulloblastoma Papilloma Ependymoma

27. Intra-axial and intraventricular lesions Primary central nervous system lymphomas may be either intra- or extra-axial in the CPA. At imaging they appear with an intermediate to low signal intensity on T1WI that strongly and homogeneously enhances after contrast. Characteristic T2 low signal intensity in about 75% of the cases, it is due to the high cellularity of this tumor, there is high signal intensity on DWI due to restriction diffusion. Metastasis may be extra-axial and mimic a meningioma or a schwannoma in the CPA, may be intra-axial exactly located in front of the IAC, often surrounded by peritumoral edema. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lymphoma Glioma Metastasis Hemangioblastoma Medulloblastoma Papilloma Ependymoma

28. Intra-axial and intraventricular lesions Choroid plexus papilloma in adult are located in the posterior fossa. Although they commonly arise from the fourth ventricle, occasionally extend into the CPA through the foramen of Luscka or primarily occur there. They appear either as homogeneous or heterogeneous cauliflower-like tumors, iso/hypointense on T1 and T2WI and strongly enhance after contrast. Ependymomas may be either spinal, supratentorial or infratentorial, with a predilection for the IV ventricle in the latter location. More frequently than papillomas, ependymomas extend into the CPA by means of an exophytic component coming from the fourth ventricle through the foramen of Lushka, a pattern very suggestive of the diagnosis. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lymphoma Glioma Metastasis Hemangioblastoma Medulloblastoma Papilloma Ependymoma

29. Intra-axial and intraventricular lesions Ependymomas appear heterogeneous with T1 hypointensity, T2 iso/hyperintensity and heterogeneous enhancement. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lymphoma Glioma Metastasis Hemangioblastoma Medulloblastoma Papilloma Ependymoma

30. Choroid plexus papilloma CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lymphoma Glioma Metastasis Hemangioblastoma Medulloblastoma Papilloma Ependymoma Intraventricular mass with involvement through left Luscka foramen to CPA angle, low signal intensity on T2WI and GRE due to hemorrhage, mild enhancement after contrast T1WI+G T1WIT2WI FLAIR DWI GRE

31. Ependymoma CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lymphoma Glioma Metastasis Hemangioblastoma Medulloblastoma Papilloma Ependymoma T1WI+G T2WI T1WI Heterogeneous cystic and solid mass involving the right CPA angle with enhancement, mass effect and obliteration of IV ventricle

32. Skull base lesions involving CPA angle CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Paraganglioma Chondromatous tumors Chordoma Endolymphatic sac tumor Most paragangliomas result from the extension from jugular foramen (glomus jugulare) or in the middle ear (glomus tympanicum). On imaging appear as highly vascular soft tissue lesions demonstrating a mix of multiple punctate and serpentine signal void corresponding to high-flow intratumoral vessels and foci of high signal intensity on T1 due to hemorrhages with methahemoglobin, producing the classic “salt and pepper” appearance.

33. Glomus yugulotympanicum CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Paraganglioma Chondromatous tumors Chordoma Endolymphatic sac tumor T1WI+G T2WI DWI T1WI Heterogeneous mass in the left jugular foramen, middle ear, EAC, with permeative and destructive involvement, “salt and pepper” appearance

34. Skull base lesions involving CPA angle CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Paraganglioma Chondromatous tumors Chordoma Endolymphatic sac tumor Endolymphatic sac tumors are aggressive papillary adenomatous tumors that originate from the endolymphatic sac, which is located at the posterior aspect of the petrous bone. These tumors may grow large enough to extend into the CPA and eventually compress the brain stem. At MR, these lesions are hyperintese on T1 and heterogeneous signal on T2WI, with foci of high signal intensity due to intratumoral subacute hemorrhage. At T1 and T2 hyperintense cystic component, rich in blood and proteins, may be present and is suggestive of the diagnosis in this very specific location.

35. Endolymphatic sac tumor CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Paraganglioma Chondromatous tumors Chordoma Endolymphatic sac tumor T2WI T1WI+G T1WI Permeative destructive retrolabyrinthine mass, hyperintense on T1 due to hemorrhage and heterogeneous enhancement after contrast

36. T1WI high signal intensity lesions CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 An intrinsic T1WI high signal intensity of non-enhancing CPA mass lesion favours a fatty or high protein content. T1WI sequence with fat signal suppression should then be performed in order to distinguish the exact nature of the high signal intensity: if it suppressed, the tumor contains fat and is likely to be a lipoma or a dermoid cyst, if it is unchanged, the lesion has a high protein content and may be a neuroenteric cyst or a cholesterol granuloma. Lipoma Neuroenteric cyst Cholesterol granuloma

37. T1WI high signal intensity lesions CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lipomas are benign lesions believed to result from a maldifferentiation of the primitive meninx. Intracranial lipomas may be asymptomatic, incidentally discovered on brain imaging. They can produce symptoms by compressing the adjacent cerebral structures, such as the cranial nerves in the CPA. Lipomas on MRI are homogeneous very high signal intensity on T1WI, which decreases on fat-suppressed image, while no enhancement is observed after contrast. Lipoma Neuroenteric cyst Cholesterol granuloma

38. Lipoma CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lipoma Neuroenteric cyst Cholesterol granuloma T1WI+G T2WI T1WI FAT SAT FLAIR T1WI Extra-axial lesion with high signal intensity on T1 and T2WI, with low signal on FAT SAT sequence without enhancement

39. Lipoma CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lipoma Neuroenteric cyst Cholesterol granuloma DWI T2 steady state There is encasement of VII, VIII cranial nerves and AICA loop

40. T1WI high signal intensity lesions CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Neuroenteric cyst are congenital cystic masses lined by a mucin- producing epithelium of endodermal origin, closely resembling gastrointestinal tract mucosa. Intracranial neuroenteric cyst are very unusual, mainly located near the midline in the posterior fossa or in the CPA. The signal intensity depends on its protein content. It can rarely mimic CSF when this content is low. Neuroenteric cysts very rarely show peripheral rim enhancement. On DWI low signal intensity. Lipoma Neuroenteric cyst Cholesterol granuloma

41. T1WI high signal intensity lesions CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lipoma Neuroenteric cyst Cholesterol granuloma Cholesterol granulomas result from the chronic obstruction of air cells and the subsequent accumulation of their secretions. In case of petrous apex origin, they can become large enough to expand in the CPA where they can compromise cranial nerves. They appear as expansil lytic lesions of the temporal bone with sharp and smooth margins, demonstrating a central region of high signal intensity and a peripheral hypointensity rim on both T1- and T2WI, corresponding to the association of the expanded cortical bone and hemosiderin deposits.

42. Cholesterol granuloma CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Lipoma Neuroenteric cyst Cholesterol granuloma T2WI DWI FLAIR T1WI Expansile petrous apex lesion with High T1 and T2 signal, there is not restriction on DWI

43. Non enhancing lesions low T1WI Epidermoid cyst are congenital lesions arising from the accidental inclusion of ectodermal epithelial tissue during neural tube closure in the first weeks of embriogenesis. About half of intracranial epidermoid cyst are located in the cerebellopontine angle, where they represents 5% of overall lesions and the third most common mass behind VS and meningiomas. These kind of lesions insinuate into posterior fossa cisterns, encasing cranial nerves and vessels with a specific irregular lobulated cauliflower-like outer surface. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Epidermoid cyst Arachnoid cyst

44. Non enhancing lesions low T1WI At MR epidermoid cysts have a fluid like low T1 signal intensity and high T2 signal intensity, but they are slightly brighter than CSF on both T1 and T2WI. DWI is specific for extra-axial epidermoid cysts by showing a very high signal. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Epidermoid cyst Arachnoid cyst

45. Epidermoid cyst CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Epidermoid cyst Arachnoid cyst T1WI+G T2WI T1WI DWI FLAIR Mass involving the occipital bone with mass effect, displacement of the left cerebellar hemisphere, CPA, heterogeneous low T1 signal with classic restriction diffusion on DWI

46. Epidermoid cyst CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Epidermoid cyst Arachnoid cyst T2WI DWI T1WI Midline lesion with intra and extra- axial involvement, extending on the left CPA angle with low signal on T1 and high signal on T2, high signal on DWI due to restriction diffusion

47. Non enhancing lesions low T1WI Arachnoid cyst are congenital, benign, intra-arachnoid puch-like lesions filled with CSF. 10% of arachnoid cyst are located in the posterior fossa, where they most commonly develop in the CPA. The large majority of arachnoid cyst are asymptomatic and found incidentally at imaging, but they can compromise cranial nerve functions in the posterior fossa by stretching them. At imaging, attenuation and signal intensities of uncomplicated arachnoid cyst exactly match those of CSF on all sequences, do not enhance after contrast media administration. On DWI there is not restriction diffusion. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Epidermoid cyst Arachnoid cyst

48. CPA lesionsEnhancingExtra-axial Intra-axial and intraventricular Skull baseNon enhancingHigh T1Low T1 Epidermoid cyst Arachnoid cyst DWI T2WI T1WI+G T1WI FLAIR Extra-axial lesion on the right CPA angle with CSF signal and without enhancement

49. Summary The vast majority of lesions involving CPA angle are VS, meningiomas, arachnoid cyst, epidermoid cyst, but there are unusual lesions that could be challenging. These kind of lesions could be incidentally but sometimes may be associated to symptoms of posterior fossa and cranial nerves involvement. Basic sequences and fat suppressed sequences and DWI must be analyzed for an adequate approach. Lesions involving CPA angle could be classified according if there is enhancement or not, intra and extra-axial location of a lesion must be considered for differential diagnosis.

50. Thank you

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