Imaging of Infratentorial brain tumors.

1. INFRATENTORIAL BRAIN TUMORS

2. ANATOMY OF POSTERIOR CRANIAL FOSSA
Posterior Fossa
Medulla
Pons
Cerebellar
hemispheres
Vermis
CSF containing
spaces
Postero-
laterally

14. INFRATENTORIAL TUMORS
 Common in children.
 In children:
 Cerebellar astrocytoma (1/3rd) and Medulloblastoma(1/3rd) > Brain stem
gliomas(1/4th) > Ependymoma(1/8th)
 Adults:
 Mostly extra-axial.
 Schwannoma> Meningioma > Epidermoid.
 Intra-axial neoplasm: Metastasis>Hemangioblastoma>Glioma

15. IMAGING
 Primary imaging modality : Magnetic resonance imaging (MRI).
 Superior delineation of the extent of tumor.
 Computed tomography: Better demonstration of small or subtle calcifications within
tumors.

16.  Determine whether the mass is intra-axial or extra-axial in location.
 Features suggesting that the mass is extra-axial include:
Bone and meninges
• Dural tail sign.
• Erosion, invasion or
destruction of adjacent
bone.
• Hyperostosis.
Brain parenchyma
• Absence of claw sign.
• Intervening cortex
between mass and
white matter.
Subarachnoid space:
• CSF cleft sign.
• Widening of adjacent
subarachnoid space/cistern.
• Intervening pial
arteries/veins.

17. CLASSIFICATION OF INFRATENTORIAL TUMORS
Location Tumors
Cerebellar hemisphere and vermis Medulloblastoma
Ependymoma
Pilocytic Astrocytoma
Hemangioblastoma
Atypical teratoid/rhabdoid tumor
Metastasis
Dysplastic Cerebellar Gangliocytoma
Rare tumors (Glioblastoma multiforme,
Gliosarcoma)
Brainstem and cervicomedullary junction Brainstem Gliomas
Primitive Neuroectodermal Tumor (PNET)
Rare tumors (Ganglioglioma)

18. Location Tumors
Cerebellopontine angle and internal auditory canal Vestibular Schwannoma
Meningiomas
Epidermoid and dermoid
Facial nerve schwannomas
Metastatic disease
Primary exophytic parenchymal neoplasms
Arachnoid Cyst
Rare (endolymphatic sac tumor, lipoma,
chordoma, melanocytoma, paraganglioma)
Fourth Ventricle Medulloblastoma
Ependymoma
Epidermoid
Choroid plexus papillomas
Subependymoma
Posterior Fossa and skull base Paraganglioma
Meningioma
Schwannoma

19. CEREBELLAR HEMISPHERE AND VERMIS

20. MEDULLOBLASTOMA
 Malignant primitive neuroectodermal tumor.
 Midline tumors
 Most common site: Vermis and Inferior medullary velum.
 Less common: Cerebellar hemisphere(Older patients)
 Most common malignant posterior fossa tumor in children(one-thirds of childhood
pediatric tumors).
 Age group: 5-15 years.
 Clinical presentation: With features of raised intracranial pressure.
 CSF seeding and Leptomeningeal metastatic spread +.

21. Histologically Defined Medulloblastomas:
 Classic medulloblastoma and
 Medulloblastoma histopathologic variants:
(1) Desmoplastic/nodular medulloblastoma.
(2) Medulloblastoma with extensive nodularity.
(3) Large cell/anaplastic medulloblastoma.
Genetically Defined Medulloblastomas
• WNT-activated medulloblastoma
• SHH-activated medulloblastomas
○ TP53 mutant
○ TP53 wild-type
• Non-WNT/non-SHH medulloblastomas
○ Group 3 medulloblastoma
○ Group 4 medulloblastoma

22. IMAGING FEATURES
 Well-circumscribed midline mass filling the fourth ventricle.
 Midline extension through the foramen of magendie into the cisterna magna may
occur.
 Lateral extension is uncommon.
 Peritumoral edema.
 Obstructive hydrocephalus with periventricular accumulation of CSF(Best delineated
on FLAIR.)
 Calcification + (in 20%).
 Cystic and necrotic degeneration common in adult MBs.

23. IMAGING FEATURES
CT
• Isodense or moderately hyperdense.
• Strong but heterogeneous
enhancement on CECT.
MRI
• Isointense or hypointense on T1WIs and
T2WIs.
• Signal heterogeneity on T2-WI due to
cysts, hemorrhage, necrosis and clump-like
calcifications.
• Moderate enhancement.
• High signal intensity on DWI.
• Low ADC.
Proton MR spectroscopy: Show taurine,
detectable at short echo time, and a massive
choline peak.

32. EPENDYMOMA
 Age group: 1-5 years.
 Arise from differentiated ependymal cells lining the fourth ventricle and foramina of
Luschka.
 Can present within the cerebellopontine angle.
Clinical features:
 Fill and distend the fourth ventricle, resulting in hydrocephalus and symptoms of nausea and
vomiting.
 Insinuate around and within structures, encasing vessels and lower cranial nerve --> Cause
cranial neuropathies.

33. EPENDYMOMA
4 types:
 Ependymoma (grade 2)
 Anaplastic ependymoma (grade 3)(Greater incidence of CSF dissemination at the time
of diagnosis and a poorer prognosis)
 Subependymoma (grade 1), and
 Myxopapillary ependymoma(grade 1).

34. IMAGING
CT: Irregular and lobulated isodense masses with calcification (up to 45%).
MRI:
 Heterogeneous with T1 hypointensity.
 T2 iso/hyperintensity and heterogeneous enhancement.
 Demonstrate intratumoral microcysts, necrosis or hemorrhage.
 Peritumoral edema usually absent.
 Following contrast administration: Inhomogeneous enhancement +. Rarely,
ependymomas do not enhance.
 CSF seeding is found in small percentage of the cases, less frequent than PNET.

35. Typical feature:
 Extension through the foramina of Luschka into the cerebellopontine angle (15%)
and/or
 Inferiorly through the foramen of Magendie (60%) onto the posterior aspect of the
upper cervical cord.
 MB: More bulbous extension rather than thin tongues of tissue through the foramina
as in ependymomas.
Proton MR spectroscopy:
 Elevated choline
 Reduced N-acetylaspartate (NAA)
IMAGING

37. SUBEPENDYMOMA
 Biologically benign, slow-growing intraventricular tumors.
 Origin: Astrocytes and ependymal cells.
 Mean age ~ 50 years.
Location:
 Fourth ventricle(floor)- MC
 Lateral ventricle(attached to the septum pellucidum)
 Third ventricle and even in the spinal cord.(Rare)
 Rarely produce symptoms.
 Hydrocephalus is the most common presentation.

38. SUBEPENDYMOMA
CT:
 Fourth ventricular subependymomas:
 Variable density compared to gray matter with calcifications(50-100%) and
enhancement.
 Lateral ventricle subependymomas:
 Vary in density.
 More often hypodense.
 Do not enhance and
 Calcifications in less than 10 percent.

39. SUBEPENDYMOMA
MRI:
 Fourth ventricular subependymomas:
 Origin from the floor of the fourth ventricle.
 Extension through the foramina of Luschka or Magendie.
 Hypointense or isointense to gray matter on T1.
 Isointense or hyperintense to gray matter on T2.
 Heterogeneous enhancement.
 Do not demonstrate paraventricular extension, unlike other ventricular tumors.
 PET using 18F-FDG : Hypometabolic tumor (Low cellular density and slow growth.)

40. PILOCYTIC ASTROCYTOMA
 Benign tumors of CNS (WHO Grade 1).
 Specific histologic type.
 Present in first two decades of life.
 Sites:
 Cerebellum(vermis or hemisphere)
 Hypothalamus
 Optic nerve optic chiasm.
 Brain stem
 Cerebral hemispheres.(Less common)

41. IMAGING
 Cystic mass with an enhancing mural nodule or a solid-cystic mass.
MRI:
 Variable and non-specific.
 Solid portion is hypointense on T1WI (higher than CSF intensity) and hyperintense on
T2WI.
 MR with contrast shows enhancement of the solid component.
 Absent accompanying edema or intratumoral calcification.
 Proton MR spectroscopy:Lactate peak.

44. ATYPICAL TERATOID/RHABDOID TUMOR
 Extremely rare.
 Highly malignant neoplasm of undetermined histogenesis.
 May arise at any site within the central nervous system.
 Non-specific features.
 Large lesions at presentation, with moderate- to- marked surrounding edema.
 CT:
 Solid(hyperdense) or mixed lesions.
 Areas of necrosis, cyst formation, hemorrhage and calcification may occur with
varying pattern of enhancement.

46. MR:
 Hypointense on T1WI and iso-hypo on T2WI with inhomogeneous enhancement.
 Meningeal enhancement and spinal tumor seeding common.
 Lower ADC values in MB and AT-RT compared with juvenile pilocytic astrocytomas
and ependymomas.
 Restricted diffusion + Not in the midline + CPA involvement: AT-RT > MB

47. HEMANGIOBLASTOMA
 Benign (WHO grade 1) tumor.
 Sporadic or manifestation of von Hipple-Lindau disease (VHL) in 25 percent.
Location
Cerebellum (83-86%)
Brain stem (2-5%)
Spinal cord (3- 13%)
Cerebrum (1.5%).
Other manifestations of VHL:
Retinal angioma
Renal cell carcinoma
Adrenal pheochromocytoma
Benign cysts in the lungs, liver, kidneys, and pancreas.

48. IMAGING
NCCT:
 Well marginated, cystic lesion(hypodense) with a mural nodule(isodense with the
brain parenchyma).
 Edema is usually absent.
 The mural nodule abuts the pial surface - Shows strong homogeneous contrast
enhancement.
 Solid hemangioblastomas - Hyperdense on NCCT with strong homogeneous
enhancement.

49. MRI:
 Cystic component of hemangioblastoma: Iso- or slightly hyperintense relative to CSF
on T1WI and hyperintense on T2WI.
 The nodule - Hypointense on T1WI and hyperintense on T2WI with intense
enhancement.
 DWI: Solid portions give low signal with increased ADC values.
 Extensive hypervascular tumor.
 Flow voids within and at the periphery of the tumor.

50.  Perfusion MR imaging : High rCBV ratios in these lesions (around 11)-
Significantly higher than metastases (around 5).
 Cerebral angiography: Dilated feeding arteries and a prolonged tumoral blush
corresponding to the solid portion.
 Main differential diagnosis –
 Pilocytic astrocytoma- Typically occurs in younger age group.

52. METASTASES
 Most common infratentorial intra-axial neoplasms in the adult population.
 Well-defined round masses.
 Nodular or ring enhancement (due to central necrosis).
 Multiple.
 Primary in adults: Lung and breast carcinoma > Melanoma > Renal cell carcinoma >
Thyroid carcinoma > Gastrointestinal malignancies.

53. CT: Typically hypodense.
MRI:
 Hypointense on T1WI and hyperintense on T2WI.
 Varying pattern of enhancement.
 Edema +
 Areas of hemorrhage and calcification - Variable signal on T2WI.

55. IMAGING
 Increased T1 signal intensity before contrast administration:
 Melanoma, kidney, lung, choriocarcinoma, and bowel (because of the presence of
mucin).
MR spectroscopy:
 Significantly elevated choline and very low NAA (may represent contamination from
adjacent tissues due to partial averaging).
 High lactate and lipids.
 The tissues surrounding the enhancing mass usually are normal by spectroscopy
(unlike high grade gliomas).

56. DYSPLASTIC CEREBELLAR GANGLIOCYTOMA(LHERMITTE-DUCLOS)
 Rare space occupying lesion of cerebellum.
Clinical presentation:
 Headache and hydrocephalus.
 Range in age from newborn to 74 years, with an average age of 34 years.

57. IMAGING
 Reflect the generally benign biologic behavior of these lesions.
NCCT:
 Hypodense
 May be isodense.
 Calcification +/-.
MRI:
 Cerebellar mass typically involving one hemisphere.
 Highly characteristic folial pattern (laminated, corduroy, lamellar, or striated).
 Do not enhance(Majority).

59. BRAINSTEM AND CERVICOMEDULLARY
JUNCTION

60. BRAINSTEM GLIOMAS
 Location: Pons(MC) and less frequently in the medulla.
 Clinical features:
 No sex predilection.
 Age group: 3-10 years.
 Multiple cranial nerve palsies, pyramidal tract signs, ataxia and nystagmus.

61. BRAINSTEM GLIOMAS
NCCT:
 Subtle enlargement or morphologic distortion of brainstem on CT.
 Contrast enhancement -patchy, irregular, homogeneous or absent.
 CPA cistern widening due to exophytic component producing extra-axial effect.
MR Imaging:
 Useful for diagnosis and localization of the tumor.
 Diffuse glioma: Poorly defined regions of low intensity on T1WI and high intensity
on T2WI.
 Intratumoral heterogeneity +/-.

62. BRAINSTEM GLIOMAS
 The basilar artery often engulfed by the anterior extension of the tumor.
 Contrast enhancement + in one-half of the cases - Often focal and nodular.
 Focal brainstem gliomas : Well circumscribed/ sometimes markedly exophytic.
 Dorsally exophytic lesions are grossly multicystic and often enhance intensely.
Other subtypes of focal gliomas :
 Tectal plate and cervicomedullary glioma.

67. CEREBELLOPONTINE ANGLE AND INTERNAL
AUDITORY CANAL

68. CPA TUMORS
 Frequent and represent 6–10 percent of all intracranial tumors.
 Most common: Vestibular schwannomas and meningiomas(~ 85–90 percent of all
CPA tumors.)

69. VESTIBULAR SCHWANNOMAS
 Benign and slow growing.
 NF-2 - Bilateral CN VIII schwannomas.
 Malignant degeneration – Rare- Associated with NF-1.
 Arise from the inferior vestibular nerve within the internal auditory canal (IAC).
 Clinical feature: Hearing loss or tinnitus.
Can be:
 Entirely intracanalicular
 Intracanalicular and cisternal components(‘‘Ice-cream cone’’ tumor)
 Purely intracisternal.(Rare).

70.  Histologically:
 Antony type A tissue(Compact)- low T2 signal relative to CSF.
 Antony type B tissue(Loose textured).
 MRI:
 Larger lesions:
 Heterogeneous appearance(internal necrosis/cyst formation).
 Higher signal intensity than CSF(Hemorrhagic byproducts, necrotic material, or
colloid-rich fluid).
 Predominance of Antoni Type B cells.
 Associated Extramural(arachnoid) cysts +.

76.  IAC involvement:
 Flaring of the porous acousticus.
 Expansion of the IAC.
 Acute angle with the dura.

77.  Low T2 signal intensity in vestibule.
 (Larger lesions)
 Small lesions - Homogeneous enhancement.
 Larger lesions:
 Heterogeneous enhancement(cystic spaces).
 Degeneration of the vestibular nucleus.
 Extent into the cochlea and “dural tails” of enhancement.
 After surgery, linear or somewhat nodular enhancement in the IAC may be seen.

78. MENINGIOMAS
 Second most common CPA tumor.
 Extra-axial neoplastic lesion.
 10 percent of all intracranial meningiomas arise in the posterior fossa.
 Origin: Arachnoidal cap cells.
 Arise from the posterior petrous surface or the underside of the tentorium.
 Intense enhancement is the rule.
 Relative T2 hyposignal - Characteristic of most of the lesions(especially transitional
and fibroblastic varieties)

79. IMAGING
NCCT:
 Hyperdense with focal areas of calcification.
 Dural tail(not pathognomonic)
 Bony reaction
 Obtuse angle with the dura.
 Center of the lesion located away from the IAC.
 Necrosis and cystic degeneration uncommon.
 May originate within the internal auditory canal, or even within the labyrinth.
Differentiate from schwannoma

83. EPIDERMOID AND DERMOID
 Congenital/ developmental masses.
 Arises from ectodermal heterotopia.
 Both cysts are lined with stratified squamous epithelium.
 Dermoids: Additional mesodermal elements such as hair, sebaceous and sweat glands
+.

84. EPIDERMOID CYST
 More common.
 Become quite large before becoming symptomatic.
 Extension into the middle cranial fossa results in a dumb-bell shape.
 Spread along the basal surfaces.
 Location: CPA > Parasellar region.
CT:
 CSF density and do not enhance.
 Calcification +
 Can have a faintly enhancing border.

85. EPIDERMOID CYST
MRI:
 Isointense to CSF on both T1 and T2WI.(Cholesterol in solid/crystalline state).
 The adamantinomatous craniopharyngioma typically contains cholesterol in liquid
state.
 Lamellated appearance because of surface desquamation.
 Do not enhance(Minimal rim enhancement occurs in approximately 25 percent of
cases.)
 Malignant transformation of an epidermoid (squamous cell carcinoma) is rare -
Considered if follow-up scans show significant increase in the amount of
enhancement.

87.  ‘‘White epidermoid’’ : Hyperintense on T1WI, and hypointense on T2WI
 High protein content, hemorrhage or the presence of saponified keratinized debris
or cholesterol in the liquid state.
 DD’s:
 Dermoid
 Lipoma.
Chemical shift artifact absent.
Fat saturation pulse sequence will not suppress the high signal in
epidermoid.
E
P
I
D
E
R
M
O
I
D

88.  Arachnoid cysts
Lamellate appearance.
Insinuate rather than displace.
On FLAIR: Mixed iso- to hypersignal intensities, but with poor
demarcation.
DWI: Hyperintense due to restricted diffusion (low ADC)
Useful for detecting postoperative residual epidermoid.
E
P
I
D
E
R
M
O
I
D

89. DERMOID CYST
 Extremely rare.
 Midline lesions.
 Locations: Parasellar, Frontobasal region or posterior fossa (vermis or fourth
ventricle).
 CT: Fat density
 Do not enhance on contrast administration.
 Associated with bone defect in nasofrontal or occipital region- Dermal sinus tract.

90.  MRI:
 Unruptured cysts – Hyperintense.
 Heterogeneous signal intensity on T2WI(hypo- to hyperintense.)
 Chemical shift artifact +
 DD: Lipoma
 Rupture of the cyst --> Chemical meningitis.
 Fat-like leptomeningeal and intraventricular deposits.
Less lobulated than lipomas.
Displace blood vessels and neural structures(encasement in
lipomas.)
D
E
R
M
O
I
D

91. ARACHNOID CYSTS
 Congenital, benign, intra-arachnoid pouchlike lesions filled with normal CSF.
 Origin : Uncertain.
 Usually supratentorial(70 percent in the temporal fossa, mostly on the left
side,anterior to the temporal poles.)
 10 percent in the posterior fossa(CPA).
Clinical presentation:
 Mostly: Asymptomatic and incidental finding.
 Compromise of cranial nerve functions.
 Spontaneous or traumatic intracystic hemorrhage.

92. IMAGING
 Attenuation and signal intensities of uncomplicated arachnoid cysts exactly match
those of CSF on all sequences.
 No enhancement.
 DD: Epidermoid cyst.
Complete suppression of signal intensity on FLAIR sequence.
DWI: Lack of diffusion restriction.
ARACHNOID
CYST

94. FACIAL NERVE SCHWANNOMAS
 Arise anywhere along the course of the nerve from the CPA to the stylomastoid
foramen.
 Arising in the IAC or CPA – Difficult to differentiate from vestibular schwannoma.
Enhancing component extending along the labyrinthine
segment of the facial nerve to the geniculate ganglion.
FACIAL NERVE
SCHWANNOMA

95. CEREBELLOPONTINE ANGLE/INTERNAL AUDITORY
CANAL LIPOMAS
 Rare lesions.
 Mesodermal inclusions.
 MRI: T1 hyperintense.
 DD: Hemorrhagic masses.

96. METASTATIC DISEASE
 Leptomeningeal(Diffuse, nodular or mass-like) OR
 Parenchymal (brainstem, cerebellum).
 Breast and lung primaries predominate.

97. PRIMARY PARENCHYMAL NEOPLASMS
 Infiltrative intraaxial component with an exophytic component resulting in a CPA
mass.
 Childhood neoplasms - MB, astrocytoma(MC), and ependymoma.

98. ENDOLYMPHATIC SAC TUMOR
 Papillary adenomatous tumors.
 Origin: Endolymphatic sac(Distal portion of the vestibular aqueduct of the petrous
bone.)
 Sporadic
 Frequent in von Hippel–Lindau disease.
 Hypervascular tumor.
CT:
 Destruction of retrolabyrinthine petrous bone.
 Geographic or moth-eaten margins.
 Intratumoral spiculated or reticulated bone.

99. ENDOLYMPHATIC SAC TUMOR
MRI:
 Heterogeneous on both T1 and T2WIs.
 Focal high signal intensity due to subacute hemorrhages.
 Low signal intensity due to calcification or hemosiderin.
 Blood-filled cysts and protein-filled cysts - Hyperintense on T1 and T2WIs.
 Heterogeneous enhancement.
 Flow voids within and around(> 2 cm in diameter) - Hypervascular.

101. PARAGANGLIOMA
Extension of paragangliomas arising at :
 Jugular foramen (glomus jugulare tumor) or
 Middle ear (glomus tympanicum tumor)
 Benign, locally aggressive tumor
CT:
 Destroy the bones of the skull base with a moth-eaten erosion pattern.

102.  MRI:
 Highly vascular soft tissue lesions.
 Mix of multiple punctuate and serpentine signal voids
(High-flow intratumoral vessels)
 Foci of high-signal intensity
(Intratumoral hemorrhages with methemoglobin).
 Perfusion MR imaging:
 High vascularity patterns with high rCBV.
 Conventional angiography:Intense tumoral blush with enlarged feeding arteries.
Salt-and-pepper appearance

104. FOURTH VENTRICLE

105. CHOROID PLEXUS PAPILLOMA
 Origin: Choroid plexus epithelium.
 Most frequent in first year of life.
 Hydrocephalus.
 Common site of origin : Lateral ventricles.
 Commonest site of adult CPP: Fourth Ventricle

106. CHOROID PLEXUS PAPILLOMA
 Well-defined lobulated masses.
 Enlargement of the involved ventricles.
 Foci of small hemorrhages and calcification may be found.
 Anaplastic papillomas, frequently invade the brain – Difficult to differentiate from
carcinomas.
 Metastasis through CSF pathways is common for both anaplastic papillomas and
carcinomas.

107. CHOROID PLEXUS PAPILLOMA
NCCT: Typically isodense to hyperdense with occasional foci of calcification.
 Homogenous enhancement is seen following intravenous contrast.
 Anaplastic CPP:
 Invade the ependyma and grow into the surrounding white matter, producing
vasogenic edema.
 Irregular in outline and closely resemble CPC.
 Hydrocephalus.

108. CHOROID PLEXUS PAPILLOMA
MRI:
 Either homogeneous or heterogeneous cauliflower-like tumors.
 Iso/hypointense on T1 and T2WI and strongly enhance after contrast injection.(Unless
highly calcified).
 Areas of low signal intensity(Calcifications).
 Foci of high signal intensity(Intratumoral hemorrhage).
 Flow voids(high flow vessels).

110. CHOROID PLEXUS CARCINOMA
 More aggressive than papillomas.
 Irregular in contour.
NCCT:
 Mixed density on pre-contrast study.
 Variable enhancement.
 Cysts and hemorrhage is frequent.
 Grow through the ventricular wall into the brain with associated edema.

111. Posterior fossa tumor
Location
Cerebellar hemispheres Brainstem Fourth ventricle Foramen of Luschka/CPA
What is
the ADC
What is
the ADC
What is
the ADC
Low ADC High ADC Low ADC High/Intermediate ADC Low ADC
Almost
extraaxial
Extra-axial +/-
multiple enhancing
nodules
Medulloblastoma
SHH
Desmoplastic
Medulloblastoma
SHH
Solid and
/or cystic
areas
Pilocytic
astrocytoma
Not
enhancing
<3 years
Multiple
enhancing
nodules
Enhancing
>3 years
Cystic/Hemorrhagic
/Calcific areas
Age < 3
years
Group 4 MB
or AT-RT
Desmoplastic
Medulloblastoma
SHH
Medulloblastoma
all the subgroups
Ependymoma AT-RT
Medulloblastoma
WNT
Yes No

112. REFERENCES
 AIIMS-MAMC-PGI IMAGING COURSE SERIES DIAGNOSTIC RADIOLOGY Neuroradiology Including
Head and Neck Imaging.
 OSBORN’S BRAIN IMAGING, PATHOLOGY, AND ANATOMY, SECOND EDITION.

113. THANK YOU