The most common location of medulloblastoma is a dense,
round mass in the fourth ventricle.MB subgroups arise in distinct regions of cerebellum,associated with subgroup-specific genetic aberrations
and cells of origin :
- Midline (4th ventricle) : predominantly (but not exclusively) groups 3 and 4
- Cerebellar/peduncle /cerebellopontine angle cistern: WNT most common
- Cerebellar hemispheres (lateral):SHH (slightly > 50%,
remainder mostly midline).
Imaging findings on non-contrast tomography:
-
Solid mass in the 4th ventricle : 90% hyperdense,
Ca ++ in up to 20%,
rare hemorrhage,
small intratumoral cysts / necrosis may occur in 40-50%;
-
Hydrocephalus (95%).
On contrast tomography findings,
90% improve relatively homogeneously and occasionally unevenly (may fill slowly)
MR Findings :
- T1WI: hypointense to gray matter (GM)
- T2WI : near GM intensity,
or slightly hyperintense to GM
- FLAIR:hyperintense to brain,
good differentiation of tumor from CSF in 4th ventricle
- DWI :restricted diffusion,
low ADC
- T1WI C+ : > 90% enhance (group 4 minimal/no enhancement),
often heterogeneous
- Contrast essential to detect CSF dissemination: linear icing-like enhancement over brain surface:"Zuckerguss",
extensive grape-like tumor nodules common in desmoplastic or medulloblastoma with extensive nodularity (MBEN),
may have dural tail and resemble meningioma (cerebellar hemispheres)
- Contrast-enhanced MR of spine (entire neuraxis) :Up to 1/3 have subarachnoid metastatic disease at presentation,
image preoperatively to avoid postoperative falsepositive: Blood in spinal canal may mimic or mask metastases
MR-Spectroscopia findings: ↓ ↓ NAA,↑ ↑ choline,
lactate usually present,
elevation in Tau (short TE),
Cr/Cho < 0.75 and mI/NAA < 2.1 indicative for MB (resembles ependymoma).
The best imaging tool is Contrast-enhanced on MR.
Typically in medulloblastoma magnetic resonance imaging (MRI) demonstrates a midline/paramedian cerebellar mass that enhances after administration of contrast and can often compress the fourth ventricle (Figure 1).
In some cases,
the clinical presentation can mimic other diseases such as stroke (Figure 2).
Recurrence can occur and leptomeningeal dissemination is an uncommon finding (Figure 3).
Fig. 1: 1a,1b,1c. Typical case of medulloblastoma with midline cerebellar mass that shows enhamce,emte after administration of contrast.
Fig. 2: AVC mimics; 44 yo male, cocaine user, dysarthria and submitted to a thrombolysis. Fig 2a-2b : axial DWI and T1WI post GD: some areas of restride diffusion and enhacement on left insula. Fig.2c and 2d: axial DWI and T!WI post GD: Multiple leptomeningeal nodules with restricted diffusion and enhacement ( orange arrows). Fig 2e- Sagital T1WI post GD: multiple leptomeningeal nodules spread along the neuro axis.
Fig. 3: 35 yo male, recurent medulloblastoma with diffuse osseous metastases and leptomeningeal spread four yaeras after resection and radioterapy. Fig. 3a-3b: Sagittal Spine T1WI and STIR: multiple osseous and leptomeningeal lesions. Fig 3c-3d: Brain axial T1WI post GD -recurrence at site and multiple leptomeningeal lesions.
Differential diagnoses
Atypical teratoid/rhabdoid tumor (AT/RT)
Top differential diagnosis (indistinguishable by imaging)
Atypical rhabdoid teratomas are usually a heterogeneous mass in young child / woman,
moderately large massive tumor with solid cyst mixed components.
The location can be:
- Infratentorial (47%): most off midline,
cerebellopontine angle (CPA),
cerebellum & / or brainstem;
- Supupentorial (41%): hemispheric or suprasellar,
both infra- and supratentorial (12%),
15-20% present with disseminated tumor at the time of initial diagnosis.
The size can be at most 1-3 cm at presentation (can be very large) and the morphology is generally roughly spherical,
irregular / lobulated.
Imaging findings on CT:
- Imaging findings on non-contrast tomography: hyperattenuating mass,commonly contains cysts and/or hemorrhage,
may contain Ca++,
obstructive hydrocephalus common.
- On contrast tomography findings: strong but heterogeneous enhancement typical.
MR Findings :
- T1WI : heterogeneous,
isointense to brain,
± hyperintense hemorrhagic foci,
cysts slightly hyperintense to CSF
- T2WI : heterogeneous,
hypointense foci (hemorrhage),
hyperintense foci (cysts)
- FLAIR: solid tumor isointense to hyperintense,
cysts hyperintense to CSF,
transependymal edema from hydrocephalus,
relatively little edema for size of tumor
- T2* GRE : hypointense "blooming" of hemorrhagic foci
- DWI: may restrict because of cellularity,
decreased apparent diffusion coefficient (ADC)
- T1WI C+ : heterogeneous enhancement,
leptomeningeal spread common (15-20%) is diffuse linear and multiple nodular,"Brain-to-brain" parenchymal metastases
- MRA : may show narrowing of encased vessels
- MR -Spectroscopy: aggressive metabolite pattern,
elevated choline,
low or absent N-acetylaspartate (NAA),
creatine,
lipid/lactate peak common
Entire CNS must be imaged at presentation to identify subarachnoid spread of tumor.
Fig. 4: Male, 2 yo, Atypical teratoid / rhabdoid tumor .5a) FLAIR, 5b) GRE * 5c) T1WI, 5d) T1WI pos-GD, 5e) T2WI axial, 5f) T2WI coronal, 5g) DWI, 5h) ADC -map. Heterogeneous contrast impregnation lesion in the left frontal lobe with diffusion restriction, with hyposinal foci in the Gradient sequence. The lesion causes median line deviation with compression of the III ventricle with hydrocephalus.
Fig. 6: Male, 2 yo.The same patient figure 4- postoperative period of the Atypical teratoid / rhabdoid tumor.5a)FLAIR, 5b) GRE* 5c)T1WI, 5d) T1WI pos-GD, 5e) T2WI axial, 5f) T2WI coronal, 5g) DWI, 5h) ADC-map.
Fig. 5: Male, 2 yo.The same patient figure 4- postoperative period of the Atypical teratoid / rhabdoid tumor on TC.
Ependymoma
Intracranial ependymomas,
including both infra- and supratentorial ependymomas,
generally demonstrate low T1,
high T2,
and intermediate-to-high FLAIR signal intensity relative to both gray and white matter .These characteristics have been attributed to the high proportion of ependymomas with intracellular myxoid accumulation and cyst formation .
They mainly affect the pediatric range with peak incidence between 1 and 15 years of age.
There is a slight predominance in boys (3,
2).
corresponds to about 10% of all pediatric tumors of the CNS,
with a predominantly infratentorial location.
The location can be:
- May arise along entire neuraxis (hemispheres,
hindbrain,
spinal cord)
- 2/3 posterior fossa (most in 4th ventricle): usually from inferior 1/2 of 4th ventricle,
extends anterolaterally through foramina of Luschka,
- 1/3 supratentorial:majority outside ventricles,
in periventricular white matter (WM)
The infratentorial ependymomas usually have a size of 2 to 4 cm.
The infratentorial ependymoma accommodates to shape of ventricle.The typical is lobulated inferior 4th ventricle mass: anterolateral extension through recess(es) into CPA cistern and posteroinferior extension through foramen of Magendie into cisterna magna.
The imaging findings of the infratentorial ependymomas are:
Imaging findings on CT:
- Imaging findings on non-contrast tomography: 4th ventricle mass ○ Ca++ common (50%); ± cysts,
hemorrhage,
Hydrocephalus common
- On contrast tomography findings: variable heterogeneous enhancement
MR Findings
- T1WI: heterogeneous,
usually iso- to hypointense,
cystic foci slightly hyperintense to CSF,
hyperintense foci (Ca++,
blood products) common
- T2WI: Heterogeneous,
usually iso- to hyperintense,
hyperintense cystic foci ○ Hypointense foci (Ca++,
blood products)
- FLAIR: can show sharp interface between tumor,
CSF,
tumor cysts very hyperintense to CSF.
- T2* GRE:"Blooming" of Ca++,
hemorrhage
- DWI: no restriction (relatively low cellularity),
intratumoral hemorrhage may complicate appearance
- T1WI C+: enhancement – Varies from none to mild/moderate – Typically heterogeneous
- MR-Spetrocopy: ↓ NAA,
↑ Cho – NAA:Cho ratio higher than in primitive neuroectodermal tumor-medulloblastoma (PNET-MB),
↑ lactate.○ MR spectroscopy alone does not reliably differentiate ependymoma from astrocytoma or PNET-MB
Fig. 7: Male, 22 years, Ependymoma. 7a)T1WI pos-GD, 7b)T2WI, 7c) DWI, 7d) ADC map, 7e)T1WI, 7f) T1WI axial pos-GD,g)T1WI sagittal pos-GD, h) T1WI coronal pos-GD.This figure shows an IV lesion in the ventricle, slightly heterogeneous, predominantly hyperintense in T2 / FLAIR and hypointense in T1, with hypointense internal areas T2 gradient (calcification / hemosiderin). Highlights of the contrast medium. No diffusion restriction. This lesion measures approximately 2.6 x 2.1 x 2.1 (CC x LL x AP), previously displaces the bridge, fills the fourth ventricle, deforming it.
Pilocytic Astrocytoma (PA)
Pilocytic astrocytoma accounts for 2% to 6% of all brain tumors.
is the most common pediatric glioma,
80 % occurring in the first two decades of life,
with a peak incidence in the age group 5 to 15 years.
In the brain,
approximately 40% of cases appear in the supratentorial compartment.
In the pediatric age group,
pilocytic astrocytoma occupies second place in frequency among those located in the infratentorial compartment.
However,
it is the most frequent glioma of the supratentorial compartment.
Imaging findings on CT:
-
Imaging findings on non-contrast tomography: Discrete cystic-solid mass ( May have little or no surrounding edema,
Solid component hypo- to isodense to gray matter (GM),
Ca++ in 20%,
hemorrhage uncommon,
often causes obstructive hydrocephalus,
location dependent,on contrast tomography findings: strong but inhomogeneous enhancement,
irregular central nonenhancing area in ⅓.
-
On contrast tomography findings:> 95% enhance (patterns vary),– 50% nonenhancing cyst,
strongly enhancing mural nodule,
40% solid with necrotic center,
heterogeneous enhancement,
10% solid,
homogeneous,
Cyst may accumulate contrast on delayed images,
Cyst wall may have some enhancement
MR Findings
- T1WI :Solid portions iso-/hypointense to GM,
cyst contents iso- to slightly hyperintense to cerebrospinal fluid (CSF)
- T2WI : Solid portions hyperintense to GM,
cyst contents iso-/hyperintense to CSF,
optic pathway hyperintense to GM
- FLAIR : Solid portions hyperintense to GM,
cyst contents do not suppress: Hyperintense to CSF,
margins of chiasmatic/hypothalamic tumors in patients with neurofibromatosis type 1 (NF1) difficult to resolve
- DWI :Solid tumor has similar diffusivity to GM
- T1WI C+: Intense but heterogeneous enhancement of solid portion,
cyst wall occasionally enhances,
Leptomeningeal metastases is rare,
optic pathway: Variable enhancement.
- MR-Spectroscopy: Aggressive-appearing metabolite pattern,
↑ choline,
↓ NAA,
↑ lactate,
paradoxical finding: MRS does not accurately reflect clinical behavior of tumor
Fig. 8: Female, 16 yo, .Pilocytic Astrocytoma (PA). Expanded heterogeneous expansive lesion undefined supra-seal the pituitary stalk, with cranial extension, obliterating the foramina of Monro, in close contact with the supraclinoid internal carotid arteries, anterior cerebral, as well as with the anterior aspect of the basilar artery. The lesion is subsequently insinuated near the interpendicular cistern, significantly displacing and compressing the cerebral peduncles. This lesion is predominantly hyperintense T2, with important peripheral enhancement after administration of gadolinium, suprasellar endovenous contrast medium, without evidence of coarse calcifications or restriction to the diffusion of water molecules.
Fig. 9: The same patient figure number 8. Female, 16 yo, .Pilocytic Astrocytoma (PA). 9a) Axial T1WI, 9b)Axial T1WI pos-GD, 9c)Sagittal T1WI, 9d)Sagittal T1WI pos-GD
Fig. 10: Female, 16 yo, .Pilocytic Astrocytoma (PA). The proton spectroscopy study was performed with ROI at the center of the lesion, demonstrating a high lipid / lactate peak, but this location prevents adequate evaluation of the other metabolites.The brain perfusion study showed hypervascularization of the lesion.
Fig. 11: Female, 16 yo, .Pilocytic Astrocytoma (PA). The proton spectroscopy study was performed with ROI at the center of the lesion, demonstrating a high lipid / lactate peak, but this location prevents adequate evaluation of the other metabolites.The brain perfusion study showed hypervascularization of the lesion.
Choroid Plexus Papilloma (CPP)
Choroid plexus papillomas (CPPs) are benign neoplasms of the choroid plexus,
a structure made from tufts of villi within the ventricular system that produces cerebrospinal fluid (CSF).
CPPs are commonly observed in the lateral ventricles of children,
but they can be encountered in adults.
While the vast majority of these neoplasms are benign,
a small percentage can be malignant.
CPPs comprise about 1% of intracranial neoplasms but 2-4% in children.
The most common location is the atrium of the lateral ventricle in children and the fourth ventricle in adults.
[9-13].It mainly affects children from 2 to 4 years of age,
being the most common location in the lateral ventricles.
The symptoms are usually secondary to hydrocephalus.
Most often these tumors (CPP) are located in lateral ventricle atria,
are small (2-8 mm),
rarely large cysts (> 2 cm),
usually multiple and generally bilateral.
Imaging findings on CT:
- Imaging findings on non-contrast tomography: Intraventricular lobular mass,
75% iso- or hyperattenuating,
Ca++ in 25%,
Hydrocephalus ( Overproduction of CSF → obstruction amd can be as much as 800-1,500 mL/day)
- On contrast tomography findings: Intense,
homogeneous enhancement ( Heterogeneous enhancement suggests choroid),
plexus carcinoma (no or minimal parenchymal invasion)
MR Findings
- T1WI : Well-delineated iso- to hypointense lobular mass
- T2WI:iso- to hyperintense mass,± internal linear and branching vascular flow voids,Large CPP may bury itself within brain parenchyma ( extensive invasion suggests CPCa),
hydrocephalus common
- FLAIR : bright periventricular signal,
periventricular interstitial edema due to ventricular obstruction common,
asymmetric ipsilateral T2 hyperintensity may suggest invasion and CPCa
- T2* GRE : ± foci of diminished signal if Ca++ &/or blood products
- are present
- T1WI C+:robust homogeneous enhancement,
occasional cysts and small foci of necrosis,
look for CSF dissemination
- MRA :flow-related signal within mass,
enlarged choroidal artery (trigonal mass)
- MR-Spectrosocpy: NAA absent,
mild ↑ choline,
lactate if necrotic,
Myoinositol (mI) elevation in CPP may help to distinguish from CPCa
Ultrasonographic Findings :grayscale ultrasound,
hyperechoic mass with frond-like projections,
mass echogenicity similar to normal choroid plexus,
hydrocephalus
Angiographic Findings :enlarged choroidal arteries,
prolonged vascular stain,
arteriovenous shunting
Fig. 12: 12a)Coronal T2WI, 12b) Axial T2WI, 12c) DWI, 12d)ADC, 12e)T1WI, 12f) Axial T1WI pos-GD, 12g) Sagittal T1WI pos-GD and 12h) Axial T1WI pos-GD .Shows a heterogeneously hyperintense right lateral ventricle mass with scattered hypointense flow voids indicating vascularity. The lobulated nature of the mass is striking. Axial T1WI C+ MR shows marked enhancement of the lobular mass with frond-like projections, characteristic of CPP.