cerebellopontine angle solitary occupying brain lesion

1. Dr. Shahnawaz Alam
Mch-Neurosurgery
Neuroradiological Discussion
CPA SOL

2. Brief History & examination:
• 60 yrs./F
• C/O: hearing difficulty with on & off headache x 11 months; insidious
onset and progressive
• H/o difficulty in walking ; urinary incontinence & dementia x 3months;
k/c/o HTN x 4 yrs.
• O/E: MMSE 14/30; power B/l UL 5/5, LL 4/5; Reflexes 2+ UL & LL
• Weber lateralized to left ear; Rinne- Lt. AC>BC, Rt. AC>BC

9. Cerebellopontine Angle
Masses
DISCUSSION

10. CPA Masses D/D
1. Vestibular schwannoma (Acoustic Neuroma)
2. CPA Meningioma
3. Epidermoid Cyst
4. Trigeminal Schwannoma
5
. Arachnoid Cyst
6. Aneurysm
7. Metastases
8. Skull base / Temporal bone tumors
9. Skull base infection
10. CPA Lipoma

11. • The CPA is region between the pons & cerebellum and the posterior aspect of the
petrous temporal bone
• Important structures of the CPA includes 5th,7th& 8thcranial nerves & AICA
• Most lesions of the CPA are extra-axial & located in the CPA cistern itself

12. Vestibular schwannoma (Acoustic Neuroma)
• Commonest CPA mass , 80%; More in females
• 90% are solitary , multiple schwannomas are commonly associated with NF2
• CPA (CN VIII , most commonly from superior portion of vestibular nerve), 90%/
Trigeminal nerve (CN V)
• Other intracranial sites (rare) : Intra-temporal (CN VII)/ Jugular foramen / bulb (CNs
IX , X , XI) / Spinal cord schwannoma/ Peripheral nerve schwannoma/ Intracerebral
schwannoma (very rare)

13. Radiological features:
• >2 mm difference between left and right IAC; Erosion and flaring of IAC; IAC > 8
mm
• Extension into CPA ( path of least resistance ) : ice-cream cone appearance
• Marked brainstem compression - obstructive hydrocephalus
• Significant signal heterogeneity with cystic or hemorrhagic areas is more typical
of vestibular schwannoma than meningioma

14. • Intracanalicular component representing
“the cone”
• The CPA component representing
the “ice cream”

15. CT :
• Isodense by CT
• Presents as a solid (small) or complex (large) enhancing mass with an intracanalicular
component that expands the porus acousticus and internal auditory canal
CT+C

16. CT+C , Bilateral acoustic neuroma in NF2

17. MRI :
• T1 : 70% hypointense, 30% isointense; T2 : Hyperintense
• T1+C : Dense enhancement : Homogeneous if small/ Heterogeneous if large
• May contain cystic degenerative areas +/- hemorrhage within large lesions/
Marginal arachnoid cysts

18. T1+C shows a rounded tumour in the right CPA with extension into the internal
auditory meatus , the IAM is expanded , this is the ice-cream cone sign

19. D/D CPA masses :
Schwannoma Meningioma Epidermoid
Epicenter-1 IAC Dural based CPA
CT Density-2 Isodense Hyper/Isodense Hypodense
Calcification-3 None Frequent Occasional
Porus-4
acusticus/IAC
Widened Normal Normal
T2W signal-5
intensity relative
GM
Hyperintense isodense 50% Hyperintense
Enhancement-6 Dense Dense None

20. Acoustic neuroma Meningioma Epidermoid

21. Schwannoma Neurofibroma
Origin-1 Schwann cells Schwann cells and
fibroblasts
Association-2 NF2 NF1
Incidence-3 Common Uncommon
Location-4 CN VIII > other CN Cutaneous and spinal
nerves
Malignant-5
degeneration
No % 5-10
Growth-6 Focal Infiltrating
Enhancement-7 +++ ++
T1W-8 hypointense, 30% 70%
isointense
Isointense with muscle
T2W-9 Hyperintense Hyperintense

22. CPA Meningioma :
• 10 % of CPA masses (2ndmost common); 40-60 years; 3 times more common in females
• CT:
1. Signal Intensity :Hyperdense (75%) or isodense (25%) on noncontrast CT; Strong
homogeneous enhancement (90%) (hallmark); Calcifications , 20%; Cystic areas ,
15%
2. Morphology :Round unilobulated sharp margin (most common); Dural tail :
extension of tumor or dural reaction along a dural surface; Edema is absent in 40%
because of the slow growth
1. Bony Abnormalities : 20 %; No changes (common); Hyperostosis (common); Bone
erosion ( rare , if present may indicate malignant meningioma )

23. CT+C , left CPA homogeneously enhancing meningioma
with a broad base against the petrous bone

24. CT

25. MRI :
• T1&T2 :Tumors are typically isointense with GM
• T1+C :Strong gadolinium enhancement; Dural tail (60%) is suggestive but not
specific for meningioma; Increased vascular flow voids
T1+C shows the typical appearance of a
meningioma with the flat surface against
the petrous bone and the dural tails , this
tumor is arising anterior to the left IAM ,
it may extend into the IAM as seen here.

26. Angiography :
• Spoke-wheel appearance; Dense venous filling
• Persistent tumor blush ( comes early and stays late ) = Mother’s in law sign
• Well-demarcated margins; Dural vascular supply

27. Differential Diagnosis
• CPA meningiomas can be differentiated from vestibular schwannomas by virtue
of their broad-based attachment to the petrous bone and more homogeneous
signal
• They are typically less bright on T2 and enhance uniformly
• A small tongue of tissue may extend into the internal auditory canal but there is
usually no expansion
• Peripheral (dural tail) and hyperostosis suggests meningioma

28. Epidermoid Cyst :
• 5 % of CPA masses
• Congenital lesions which account for about 1% of all intracranial tumours; result from
inclusion of ectodermal elements during neural tube closure
• Although predominantly congenital, epidermoid cysts are usually very slow growing
and as such take many years to present, typically patients are between 20 and 40
years of age
• An uncommon association exists with anorectal anomalies, sacral anomalies and pre-
sacral mass and is known as the Currarino triad
• Intradural (90 %): CPA, 40 %/ Suprasellar region /4thventricle/ Middle cranial fossa
• Extradural ( 10 % ): Most within the skull

29. CT :
Lobulated lesion with CSF
density; No enhancement

30. MRI : CSF-like signal
• T1 :Usually isointense to CSF; Higher signal compared to CSF around the periphery of
the lesion is frequently seen; Rarely shows high T1 signal (white epidermoid)
• T2 :Usually isointense to CSF (65%); Slightly hyperintense (35%)
• T1+C :No enhancement; Thin enhancement around the periphery may sometimes be
seen
• FLAIR :Often heterogeneous /dirty signal ; higher than CSF
• DWI :Useful for differentiation from arachnoid cysts due to increased signal (due to a
combination to true restricted diffusion and T2 shine through) which isn’t seen with
arachnoid cyst

31. T1 T2 T1+C

32. FLAIR DWI ADC

33. T2 shine through:
• Refers to high signal on DWI images that is not due to restricted diffusion but rather to
high T2 signal which (shines through) to the DWI image, T2 shine through occurs
because of long T2 decay time in some normal tissue
• This is most often seen with subacute infarctions due to vasogenic edema but can be
seen in epidermoid cyst
• To confirm true restricted diffusion one should always compare the DWI image to
the ADC
• In cases of true restricted diffusion the region of increased DWI signal will
demonstrate low signal on ADC
• ADC is a value that measures the effect of diffusion independent of the influence of T2
shine- through, ADC maps thus portray restricted diffusion such as in ischemic injury ,
as hypointense lesions relative to normal brain
• In contrast , in cases of T2 shine-through , the ADC will be normal or high signal

34. Epidermoid Dermoid
Content Squamous epithelium, Also has dermal
keratin, cholesterol appendages (hair,
sebaceous fat, sweat
(glands
Location Off midline Midline
CPA most common Spinal canal most common
Parasellar, middle fossa Parasellar, posterior fossa
Intraventricular, diploic
(space (rare
Rupture Rare Common (chemical
(meningitis
Age Mean 40 years Younger adults
CT density CSF density May have fat
Calcification Uncommon Common
Enhancement Occasional peripherally None
MRI CSF-like signal Proteinaceous fluid
Incidence times more common 5-10 Less common
than dermoid

35. Arachnoid cyst :
• Benign CSF-filled lesion that is usually congenital; Although most
arachnoid cysts are supratentorial , the CPA is the most common
infratentorial location
• Arachnoid cyst will follow CSF signal on all sequences including complete suppression
on FLAIR , unlike epidermoid cyst , arachnoid cyst doesn’t have restricted diffusion
• DWI allows differentiation of epidermoid and arachnoid cysts :
The ADC of an epidermoid cyst is significantly lower than that of an arachnoid cyst ,
therefore , epidermoid cysts have high signal intensity on DWI , whereas arachnoid cysts ,
like CSF , have very low signal intensity

36. Arachnoid Epidermoid
Signal intensity-1 Isointense to CSF on T1 Mildly hyperintense to CSF
Isointense to CSF on PD Hyperintense to CSF on PD
Isointense to CSF on T2 Isointense to CSF on T2
Enhancement-2 No No
Margin of lesion-3 Smooth Irregular
Effect on adjacent-4
structures
Displaces Engulfs , insinuates
Pulsation artifact-5 Present Absent
Diffusion imaging-6 Follows CSF Hyperintense to CSF
FLAIR imaging-7 Suppresses like CSF Hyperintense to CSF
Calcification-8 No May occur

37. Trigeminal schwannoma of right gasserian ganglion with smooth margins ,
relatively low signal in T1 ( A) and high homogenous signal intensity on T2 ( B )

38. T1+C shows normal non-enhancing Meckel’s cave on the right side (arrow) ,
in the left Meckel’s cave , a heterogenous enhancing mass (arrow head) is
seen extending in the cavernous sinus , trigeminal schwannoma

39. A homogeneous , enhanced , dumbbell-shaped right trigeminal schwannoma
involving the cisternal part of the nerve and Meckel cave

40. CPA Aneurysm :
• Large aneurysms arising from the vertebrobasilar system (PICA , AICA , vertebral artery
or basilar artery) may appear as well- defined avidly enhancing CPA lesion and may be
initially mistaken for a schwannoma or meningioma on CT+C
• On MRI , clues to a vascular aetiology would be flow void and pulsation artifacts , MRA
or CTA are diagnostic
Aneurysm in a 75-year-old man with hypoglossal nerve palsy , (a) T2 shows a thrombosed aneurysm of the right PICA with focal
calcification (arrowhead) , note the normal right hypoglossal canal (arrow) , a finding inconsistent with a schwannoma , (b) T1+C
shows homogeneous enhancement of the organized thrombus which completely fills the aneurysm

41. Others:
• Metastases
• Skull Base / Temporal Bone Tumors : Glomus tumors & cholesterol granuloma
• Skull Base Infection: Gradenigo's syndrome (osteomyelitis of the petrous apex) and
malignant otitis externa
• CPA Lipoma
Melanoma in a 58-year-old woman with a left cerebellar syndrome , (a) CT shows a hyperattenuating
melanoma of the left CPA , (b) T1 shows a well- defined extraaxial mass at the posterior edge of the
petrous bone , the high signal intensity is suggestive of melanin , (c) T1+C shows a normal left internal
auditory canal (arrow) and lack of dural tail enhancement

42. Paraganglioma (a) T2 shows a huge paraganglioma destroying the petrous bone
and invading the right CPA , massive flow voids (arrowheads) reflect the
hypervascularity of the lesion , note the thin layer of trapped CSF (arrow) between
the mass and the brainstem which indicates an extraaxial origin , (b) T1 shows the
suggestive salt-and-pepper appearance of the paraganglioma , (c) T1+C shows
intense enhancement of the lesion along with unusual dural tail enhancement of
the meninges (arrows)

43. CPA lipoma (a) Axial CT scan shows a well-defined hypoattenuating
lipoma of the left CPA , (b) T1 shows that the lipoma has signal
intensity similar to that of subcutaneous fat

44. Cholesterol granuloma , (a) T1 shows a cholesterol granuloma at the apex of the right
petrous bone with typical high signal intensity , an additional suggestive feature is the
thin hypointense rim (arrowheads) which represents expanded cortical bone of the
petrous apex , (b) T2 shows that the granuloma has heterogeneous signal intensity
surrounded by a hypointense rim (arrowheads) , (c) T1+C shows the normal right
trigeminal nerve (arrow) at the top of the mass

45. THANK YOU
References:
• Osborn Brain Imaging ; 2nd edition