Diagnostic Imaging of Cerebellopontine Angle Masses

1. C.N.S.
Cerebellopontine Angle Masses

2. Mohamed Zaitoun
Assistant Lecturer-Diagnostic Radiology
Department , Zagazig University Hospitals
Egypt
FINR (Fellowship of Interventional
Neuroradiology)-Switzerland
zaitoun82@gmail.com

5. Knowing as much as
possible about your enemy
precedes successful battle
and learning about the
disease process precedes
successful management

6. Cerebellopontine Angle Masses
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

7. 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
& 8th
cranial nerves & AICA
Most lesions of the CPA are extra-axial & located in the CPA cistern itself

9. 1-Vestibular schwannoma (Acoustic Neuroma)
a) Incidence
b) Location
c) Radiographic Features
d) Differential Diagnosis

10. a) Incidence :
-Commonest CPA mass , 80%
-More in females
-Benign tumor of Schwann cell origin
-90% are solitary , multiple schwannomas are
commonly associated with NF2

11. b) Location of Schwannoma :
1-CPA (CN VIII , most commonly from superior
portion of vestibular nerve), 90%
2-Trigeminal nerve (CN V)
3-Other intracranial sites (rare) :
-Intratemporal (CN VII)
-Jugular foramen / bulb (CNs IX , X , XI)
4-Spinal cord schwannoma
5-Peripheral nerve schwannoma
6-Intracerebral schwannoma (very rare)

12. c) Radiographic Features :
1-Mass
2-CT
3-MRI

13. 1-Mass :
->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 may occur and
produce 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. 2-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

17. CT+C

18. CT , Bilateral acoustic neuroma , NF2

19. CT+C , Bilateral acoustic neuroma in NF2

20. 3-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

21. T1

22. T1

23. T1

24. T1

25. T2

26. T2

27. T2

28. T2

29. 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

30. T1+C

31. T1+C

32. T1+C

33. T1+C

34. T1+C

35. T1+C

36. T1+C

37. T1+C

38. d) Differential Diagnosis :
1-From CPA masses
2-From Neurofibroma

39. 1-From CPA masses :
Schwannoma Meningioma Epidermoid
1-Epicenter IAC Dural based CPA
2-CT Density Isodense Hyper/Isodense Hypodense
3-Calcification None Frequent Occasional
4-Porus
acusticus/IAC
Widened Normal Normal
5-T2W signal
intensity relative
GM
Hyperintense 50%isodense Hyperintense
6-Enhancement Dense Dense None

40. Acoustic neuroma Meningioma Epidermoid

41. 2-From Neurofibroma :
-Plexiform neurofibromas are unique to
neurofibromatosis type 1 (NF1)
-They do not occur primarily in the cranial cavity
but may extend into it from posterior ganglia
or as an extension of peripheral tumors

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

43. 2-CPA Meningioma :
a) Incidence
b) Radiographic Features
c) Differential Diagnosis

44. a) Incidence :
-10 % of CPA masses (2nd
most common)
-Age: 40 to 60 years
-Three times more common in females

45. b) Radiographic Features :
1-CT
2-MRI
3-Angiography

46. 1-CT :
a) Signal Intensity
b) Morphology
c) Bony Abnormalities

47. a) Signal Intensity :
-Hyperdense (75%) or isodense (25%) on
noncontrast CT
-Strong homogeneous enhancement (90%)
(hallmark)
-Calcifications , 20%
-Cystic areas , 15%

48. CT

49. CT

50. CT

51. CT

52. CT

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

54. b) 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

55. c) Bony Abnormalities : 20 %
-No changes (common)
-Hyperostosis (common)
-Bone erosion ( rare , if present may indicate
malignant meningioma )

56. 2-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

57. T1

58. T2

59. T1+C

60. T1+C

61. T1+C

62. T1+C

63. T1+C

64. 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

65. 3-Angiography :
-Spokewheel appearance
-Dense venous filling
-Persistent tumor blush ( comes early and stays
late ) = Mother’s in law sign
-Well-demarcated margins
-Dural vascular supply

68. f) Differential Diagnosis : (see before)
-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

69. 3-Epidermoid Cyst :
a) Incidence
b) Location
c) Radiographic Features
d) Differential Diagnosis

70. a) Incidence :
-5 % of CPA masses
-Congenital lesions which account for about 1%
of all intracranial tumours
-They result from inclusion of ectodermal
elements during neural tube closure

71. -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

72. b) Location :
*Intradural (90 %) >>
1-CPA, 40 %
2-Suprasellar region
3-4th
ventricle
4-Middle cranial fossa
*Extradural ( 10 % ) >>
-Most within the skull

73. c) Radiographic Features :
1-CT :
-Lobulated lesion with CSF density
-No enhancement

75. 2-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 epidermoids)
*T2 :
-Usually isointense to CSF (65%)
-Slightly hyperintense (35%)
*T1+C :
-No enhancement
-Thin enhancement around the periphery may
sometimes be seen

76. *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

77. T1

78. T1

79. T2

80. T2

81. T1+C

82. T1+C

83. FLAIR

84. FLAIR

85. DWI

86. DWI

87. ADC

88. ADC

89. **N.B. : 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

90. -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

91. d) Differential Diagnosis :
1-From Dermoid cyst :
-See table

92. Epidermoid Dermoid
Content Squamous epithelium,
keratin, cholesterol
Also has dermal
appendages (hair,
sebaceous fat, sweat
glands(
Location Off midline
CPA most common
Parasellar, middle fossa
Intraventricular, diploic
space (rare(
Midline
Spinal canal most common
Parasellar, posterior fossa
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 5-10times more common
than dermoid
Less common

93. 2-From Arachnoid cyst : (See table)
-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

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

95. 4-Trigeminal Schwannoma :
-Similar in appearance to vestibular
schwannoma but arising from the V cranial
nerve

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

97. Trigeminal Schwannoma of right gasserian ganglion , relatively low
signal on T1 ( A ) and high heterogeneous signal intensity on T2 ( B )
, note normal Meckel’s cave ( curved arrow ) on ( C )

98. 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

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

100. 5-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

101. Arachnoid cyst (a) T1 shows an arachnoid cyst with signal intensity similar to
that of CSF stretching the left seventh and eighth cranial nerve complex
(arrow) , (b) T2 shows the cyst displacing the vascular structures of the
CPA (arrowheads)

102. 6-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 etiology would be
flow void and pulsation artifacts , MRA or CTA
are diagnostic

103. 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

104. 7-Metastases :
-See Brain Tumors
8-Skull Base / Temporal Bone Tumors :
-e.g. Glomus tumors & cholesterol granuloma
9-Skull Base Infection :
-Gradenigo's syndrome (osteomyelitis of the petrous
apex) and malignant otitis externa
10-CPA Lipoma :
-See brain tumors

105. 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

106. Metastases in a 67-year-old man with lung cancer, (a) T2 shows a metastasis of the
right CPA that mimics a vestibular schwannoma but with unusual associated
middle ear retention ( ) ,∗ (b) T1+C shows intense enhancement of the lesion which
extends into the cochlea (arrow) , note the presence of another enhancing lesion
at the tip of the right petrous bone (arrowhead)

107. 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)

108. 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

109. Apex petrositis in a 50-year-old woman with Gradenigo syndrome at clinical
evaluation , (a) T1 shows an irregular lesion at the tip of the petrous apex
(arrow) , (b) T1+C shows right-sided apex petrositis as an enhancing lesion
along the courses of cranial nerves V and VI (arrow)

110. 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

111. T1 shows CPA lipoma