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1. Conventional and Advanced
MRI Features of Pediatric
Intracranial Tumors: Posterior
Fossa and Suprasellar Tumors
MODERATOR:DR.BHAGYALAKSHMI M.D
PRESENTOR:N.LAKSHMI CHAITANYA

2. Posterior Fossa Tumors

3. Pilocytic Astrocytoma
• Cerebellar astrocytomas account for 30% of all posterior fossa
tumors in children, with the most common histologic subtype
being JPA.
• The majority of JPAs, 60%, arise from the cerebellum.
• Five percent of patients with neurofibromatosis type 1 (NF1) will
develop a cerebellar JPA, although the most common location for
pilocytic astrocytoma in NF1 patients is the optic nerve or optic
chiasm.

4. • The classic imaging appearance of a JPA, is of a large cyst with
a solid mural nodule within one of the cerebellar hemispheres.
• less commonly, JPA may present on imaging as a predominantly
solid mass with little to no cyst like component.
• On MRI, the cystic portion is hypointense relative to gray matter
on T1-weighted images and hyperintense relative to gray matter
on T2-weighted images.
• JPA is a low-grade neoplasm (GRADE-1)

5. • Enhancement patterns may vary, but JPA most commonly (46%)
appears as a cyst with an enhancing wall and an intensely
enhancing mural nodule.
• Diffusion-weighted imaging (DWI) of JPAs shows no restricted
diffusion, which is consistent with the characteristics of a low-
grade tumor.
• MR spectroscopy (MRS) performed on the solid portion of
pilocytic astrocytomas shows elevated choline-to–N-acetyl
aspartate (NAA) ratios and elevated lactate levels, which is an
aggressive metabolite pattern.

6. • The elevated lactate levels in JPAs do not reflect necrosis, which
is rare in pilocytic astrocytomas and, rather, reflect
aberrant glucose utilization.
• DTI has been shown to be a useful adjunct in differentiating
thalamopeduncular pilocytic astrocytomas from infiltrating tumors
in the posterior fossa because pilocytic astrocytomas displace
corticospinal tracts, whereas other tumors may encase them or
disrupt them.
• JPAs may mimic hemangioblastomas.

9. Medulloblastoma
• Medulloblastoma accounts for 35–40% of all posterior fossa
tumors in children with peak occurrence at approximately 4
years old.
• Classic medulloblastoma typically arises from the roof of the
fourth ventricle and is midline in location in 75–90% of cases.
• Desmoplastic medulloblastoma is a rare histologic variant that
typically occurs off midline in the cerebellar hemisphere.

10. • Classic medulloblastoma is a highly cellular, densely packed
tumor, which is reflected on imaging; it appears hyperdense
relative to brain on CT (89% of cases) and shows restricted
diffusion on DWI.
• Apparent diffusion coefficient (ADC) values are significantly lower
in medulloblastoma.
• This feature of medulloblastoma allows differentiation from JPA,
ependymoma, and brainstem glioma.
• Medulloblastoma is a high-grade tumor, so it can be
differentiated from low-grade posterior fossa tumors on the basis
of its increased rCBV on perfusion MRI.

11. • T2-weighted imaging shows heterogeneous signal: The solid
components appear hypointense relative to gray matter because
of the highly cellular nature of the tumor and the cystic
components, which are seen in 59% of cases, appear
hyperintense.
• Calcifications can be found in up to 20% of cases and
hemorrhage is rare.
• Enhancement may be variable in degree, ranging from diffuse
homogeneous enhancement to very little patchy enhancement.

12. • Medulloblastomas generally have the characteristic
spectrographic signature for a neuroectodermal tumor with high
taurine, depleted NAA, and prominent choline and lipid peaks.
• Because treatment of patients with medulloblastoma involves
craniospinal radiation, DTI and DWI are potentially useful in early
detection and monitoring of radiation-induced white matter injury
through the measure of fractional anisotropy (FA) and ADC
values.

13. • At diagnosis, 14–43% of patients with medulloblastoma are
reported to have microscopic or nodular seeding of the
subarachnoid space; therefore, at the time of diagnosis, an MRI
examination of the entire spine should be performed to determine
if there is leptomeningeal dissemination.

15. Atypical Teratoid-Rhabdoid Tumor
• ATRT constitutes 1–2% of pediatric brain tumors and has a
predilection for infants; it most commonly occurs in children
younger than 3 years old.
• Within the CNS, ATRT most commonly occurs infratentorial and
off midline, 38–65%; however, in 4–8% of the cases, tumors are
present at multiple CNS sites at the time of diagnosis.
• ATRT mimics medulloblastoma radiologically and histologically
and has been misdiagnosed in the past.

16. • ATRTs can now be differentiated from medulloblastomas using
specific immunohistochemical markers and by detecting certain
gene mutations or deletions, such as the lack of INI1 expression
on immunohistochemical stains.
• Conventional MRI shows heterogeneous signal intensity on T1-
and T2-weighted pulse sequences because the mass commonly
contains cysts, hemorrhage, and calcifications.
• Eccentrically located cysts may favor the diagnosis of ATRT
over primitive neuroectodermal tumor and medulloblastoma.

17. • A highly aggressive appearance of a tumor with skull invasion
may favor ATRT over other cystic masses such as JPA or
desmoplastic infantile ganglioglioma.
• The enhancement pattern of ATRTs is most commonly
heterogeneous and is rarely homogeneous, reflecting the
complex histopathology of this tumor.
• Restricted diffusion is typical.
• MRS shows an aggressive metabolite pattern with elevated
choline, decreased or absent NAA, and prominent lipid and
lactate peaks.

18. • Distinguishing between an ATRT and a medulloblastoma is
important because the prognosis associated with ATRT is worse
than that associated with medulloblastoma.
• A younger patient age, intratumoral hemorrhage, and
cerebellopontine angle involvement favor a preoperative
diagnosis of ATRT over medulloblastoma.

20. Ependymoma
• Ependymoma is the third most common posterior fossa tumor in
children.
• Incidence peaks in patients 0–4 years old.
• Approximately 70% of intracranial ependymomas are infratentorial and
arise from ependymal cells lining the floor of the fourth ventricle and
foramen of Luschka.
• Neurofibromatosis type 2 (NF2) is the only known genetic disorder
associated with a predisposition for ependymomas; however, NF2
patients typically develop the intramedullary spinal type of
ependymoma.

21. • Histologically, ependymomas tend to have a high proportion of
intracellular myxoid accumulation and cyst formation.
• These features are reflected on conventional MRI as high signal
intensity relative to uninvolved gray matter on T2-weighted and
FLAIR pulse sequences.
• Areas of low signal intensity relative to gray matter on T2-
weighted images and FLAIR images may represent calcifications
or hemorrhage.

22. • Sagittal images may be the key to the diagnosis in some cases
because sagittal images can be used to identify the point
of origin as the floor of the fourth ventricle, as seen in
ependymoma, versus the roof, as seen in medulloblastoma.
• Calcification is a common feature seen in 50% of ependymoma
cases and contrast enhancement is heterogeneous.
• Although not pathognomonic, the plastic nature of ependymoma
results in the classic presentation of a fourth ventricle mass
extending through the foramen of Luschka (15%) or foramen of
Magendie (60%).

23. • Some ependymomas may show restricted diffusion.
• Perfusion MRI patterns for ependymomas are variable and are likely
related to the histologic subtype. However, in general, perfusion MRI
of ependymomas shows markedly elevated cerebral blood volume
(CBV) and poor return to baseline CBV, which is attributable to the
fenestrated blood vessels observed microscopically.
• MRS generally shows depleted NAA and elevated choline and lactate
levels, but the primary application of MRS in the setting of
ependymoma is to evaluate for tumor recurrence versus posttreatment
change.

25. Brainstem Glioma
• Brainstem gliomas comprise approximately 10–20% of all
intracranial tumors in children and 75% of brainstem gliomas
occur in patients younger than 10 years.
• Brain stem gliomas are not designated as a specific pathologic
category in the WHO classification of CNS tumors and are
classified by location rather than histology.
• They are classified broadly as diffuse intrinsic gliomas or as
nondiffuse brainstem tumors.

26. • The diffuse intrinsic tumor type is the most common, with
an approximate frequency of 75–85%.
• NF1 patients with brainstem gliomas have a more favorable
prognosis than non-NF1 patients.
• On MRI, diffuse pontine gliomas characteristically expand the
pons and are usually hypointense relative to gray matter on T1-
weighted images and hyperintense relative to gray matter on T2-
weighted and FLAIR images.
• Most diffuse brainstem gliomas do not enhance; however if they
do enhance,enhancement is very little and heterogeneous.

27. • Most diffuse gliomas do not show restricted diffusion and ADC
values are characteristically higher than in medulloblastomas.
• Most diffuse brainstem gliomas are histologically low grade, but a
subset rapidly evolves into highgrade neoplasms; on advanced
imaging techniques, high-grade neoplasms are suggested
by focal areas of restricted diffusion and increased rCBV.
• These findings likely correspond to areas of anaplasia.

28. • Moreover, MRS shows utility in establishing a brainstem glioma’s
baseline metabolic profile so subsequent metabolic changes on
serial MRS can be used as markers for disease progression.
• Malignant degeneration is suggested by increased lipids and
reduced NAA-to-choline, creatine-to-choline, and myoinositol-to-
choline ratios.
• Importantly, identifying increased choline concentrations on
serial MRS may precede clinical worsening by up to 5 months.

29. • Diffuse intrinsic brainstem gliomas had higher mean
concentrations of citrate than ependymomas, medulloblastomas,
and JPAs.
• With respect to brainstem gliomas, DTI plays an essential role in
diagnosis and surgical planning.
• Demyelinating diseases may mimic diffuse intrinsic brainstem
gliomas clinically and on conventional imaging
techniques; however, tractography clearly distinguishes between
the two because brainstem gliomas deflect white matter tracts
whereas demyelinating diseases result in truncated fibers.

30. • Tractography allows visualization of spatial relations between
tumor and adjacent fiber tracts; in operable brainstem glioma
tumor types, tractography provides important presurgical
information because preservation of white matter tracts
correlates with better neurologic and functional outcomes after
surgery.
• Diffuse intrinsic gliomas are nonoperative. The standard
treatment is fractionated external beam radiotherapy, with
chemotherapy reserved for cases of tumor progression
despite radiotherapy.

31. • The diffuse intrinsic type has the worst prognosis of all brainstem
gliomas, with median survival rarely exceeding 9 months.
• Focal midbrain tumors have a more indolent course and a more
favorable prognosis.

33. Hemangioblastoma
• Hemangioblastomas account for 1–3% of all intracranial
neoplasms, and most occur in middle-aged adults.
• In children younger than 18 years old, these tumors are
extremely rare, with an incidence of less than 1 per 1 million.
• One of the most common manifestations of von Hippel–Lindau
(VHL) syndrome is multiple CNS hemangioblastomas, with
the most common site of presentation being in the cerebellum.

34. • Patients with cerebellar hemangioblastomas typically present
with headache, vertigo, ataxia, and ninth cranial nerve palsy; in
some cases, polycythemia has been noted given that up to 40%
have been reported to secrete erythropoietin.
• Hemangioblastomas are highly vascular tumors and may present
as a mural nodule within a large cyst cavity (45%) or a purely
solid tumor (45%).
• Typical hemangioblastomas are hypo- to isointense relative to
gray matter on T1 and hyperintense relative to gray matter on T2
with enhancement of the mural nodule.

35. • The cyst wall most commonly does not enhance unless lined by
neoplasm.
• Large feeding and draining vessels in the periphery and within
the solid component appear as tubular flow voids on T2-weighted
imaging.
• Hemangioblastomas mimic pilocytic astrocytomas
and pleomorphic xanthoastrocytomas in their imaging
appearance, but because of their intrinsic high vascularity,
hemangioblastomas have the highest rCBV thus, perfusion
MRI may be a useful diagnostic adjunct.

37. Sellar and Suprasellar Tumors

38. Craniopharyngioma
• Craniopharyngiomas are benign tumors that arise from
squamous epithelium.
• They represent 50% of suprasellar tumors in children; most
cases are diagnosed in children who are 4–5 years old, with a
second incidence peak during the fourth to fifth decades.
• Craniopharyngiomas can arise in the sellar region, suprasellar
region, or both.

39. • Because of the location of this tumor, patients commonly present
clinically with visual disturbance, due to compression of the optic
chiasm; endocrinologic disorders, from involvement of the
hypothalamus and pituitary; or headache and hydrocephalus.
• Nearly 90% of craniopharyngiomas are suprasellar, are cystic
with calcifications, and have nodular or rim enhancement on CT.
• CT is particularly helpful in the identification of these lesions
because of its high sensitivity for calcification.

40. • On MRI, the cystic component may be hypo- or hyperintense
relative to gray matter on T1 because of the liquid cholesterol
component, methemoglobin, or proteinaceous fluid.
• The solid component may be iso- or hypointense on T1-weighted
images and iso- or hyperintense relative to gray matter on T2-
weighted images.
• Calcifications usually appear as low signal on T2-weighted
imaging.

41. • The signal characteristics of craniopharyngiomas on DWI and
FLAIR imaging may vary depending on the viscosity of the fluid.
• If there is a high degree of viscosity, the tumor may appear
hyperintense on FLAIR imaging and isointense on DWI with a
slightly lower ADC than CSF.
• MRS may help differentiate craniopharyngiomas from other
suprasellar masses by depicting prominent peaks of lipids and
cholesterol.
• The differential diagnosis includes hypothalamic glioma, Rathke
cleft cyst, and germ cell tumors.

42. • Optic DTI may help in the preoperative evaluation and treatment
of craniopharyngiomas because DTI has been proven useful
in differentiating the optic nerves from chiasmatic or suprasellar
tumors.
• Normal white matter tracts are usually associated with high FA
values, which will allow depiction of the tracts by fiber-tracking
software.
• On the contrary, abnormal white matter tracts with low FA
values may not be seen on tractograph.

44. Hypothalamic Hamartoma
• Hypothalamic hamartomas are not true neoplasms.
• They are considered developmental malformations from mature
ganglionic tissue that involve the tuber cinereum.
• Clinically patients with hypothalamic hamartoma can present with
gelastic seizures, precocious puberty, and developmental delay.
• On CT, hypothalamic hamartoma appears as a homogeneous
isodense suprasellar mass.

45. • MRI, hypothalamic hamartoma can be identified by the presence
of a small, well-defined pedunculated or sessile mass.
• It is isointense relative to gray matter on T1-weighted images and
is iso- to slightly hyperintense relative to gray matter on T2-
weighted imaging, FLAIR imaging, and DWI without
enhancement or calcification.
• MRS has shown increased myoinositol levels with decreased or
normal NAA levels.
• The differential diagnosis includes germinoma and hypothalamic
glioma.

47. Hypothalamic and Chiasmatic Gliomas
• Hypothalamic and chiasmatic gliomas represent 10–15% of
pediatric supratentorial tumors, 20–50% of which are associated
with NF1.
• Histologically, they are mostly pilocytic astrocytomas and low-
grade astrocytomas and the distinction between chiasmatic origin
and hypothalamic origin may be difficult.

48. • Hypothalamic and chiasmatic gliomas appear hypointense
relative to gray matter on T1and hyperintense relative to gray
matter on FLAIR and T2 with homogeneous enhancement.
• The MRS spectral pattern is similar to those of other
astrocytomas with a dominant choline peak.
• Optic DTI is helpful for planning surgery of these tumors, as with
craniopharyngiomas, by differentiating glioma from the optic
nerve.
• The differential diagnosis includes germ cell tumors, Langerhans
cell histiocytosis, and inflammatory conditions.

49. • Hypothalamic and chiasmatic gliomas may be differentiated from
germ cell tumors by the usual hyperintense signal on T2-
weighted images compared with the hypointense signal of
germ cell tumors

50. Conclusion
• Imaging in pediatric CNS tumors is an essential component in
the care of these patients and has evolved greatly over the past
decade.We are becoming better at making a preoperative
diagnosis of the tumor type, detecting recurrence, and guiding
surgical management to avoid injury to vital brain structures.

51. Thank you