3. Epidemiology
• The most common malignant pediatric posterior fossa tumor
• Median age 6 to 9 years(during first decade)
• Can occur in adulthood
• Midline cerebellum, in the region of the mid and inferior vermis
• May spread along the cerebellar peduncles and extend upward
through the tentorial hiatus or downward into the cervical spinal
canal
• All patient must be evaluated for “drop mets”
6. Familial cancer syndromes
• Li-Fraumeni syndrome
• mutations of the p53 tumor suppressor gene
• Rubenstein-Taybi
• Aicardi’s syndrome
7. Molecular biology
• Non-random chromosomal abnormalities
• consistent deletion of 17p markers
• Information from gene profiling
• ZIC and NSCL1
• Abnormalities in signal transduction pathways
• neurotrophin signaling pathway (important in cerebellar development) or
Sonic hedgehog (Shh)
8. Pathology
• All MB are WHO grade IV
• Gross
• pinkish gray to purple mass, commonly arising from the medullary velum
• most of its blood supply from the posterior inferior cerebellar artery
• firm, discrete
• “sugar-coated” appearance of the cerebellar surface
9. Pathology
• 1.classic (90%)
• small, densely packed undifferentiated cells with hyperchromatic nuclei,
scant cytoplasm
• inconstant cell clusters in Homer-Wright rosettes
• sometimes called “blue tumor” (monotonous appearance)
• 2. Desmoplastic (6%)
• similar to classic type with “glomeruli” AKA pale islands (collagen bundles
and scattered, less cellular areas)
• Marked tendency for neuronal differentiation
• More common in adults
• Prognosis controversi11al: may be the same or less aggressive than classic MB
10. Pathology
• 3. large cell (4%)
• large, round, and/or pleomorphic nucleoli, higher mitotic activity
• In the few case reports, all were male
• More aggressive than classic
• Resembles atypical teratoid/rhabdoid tumors of cerebellum , but has
different phenotype and cytogenic features
12. Clinical finding
• Most common triad : headache, lethargy, and vomiting
• Short clinical history : 1.5 Mo, 3 Mo
• Infants and young children
• irritability, loss of appetite, weight loss, and failure to thrive
• increased intracranial pressure, including lethargy, drowsiness, vomiting,
sunsetting, a full fontanelle, or an increasing head circumference
• Older children
• headache, neck stiffness, dizziness, or diplopia
13. Clinical finding
• Neurological examination
• truncal or appendicular ataxia, dysmetria, nystagmus, or cranial nerve palsies
• A head tilt, signifying descent of the cerebellar tonsils into the foramen
magnum with compression of the C1 or C2 nerve roots
• Not specific
• Ddx : other posterior fossa lesions such as astrocytoma, ependymoma, or
cystic mass lesions
14. Diagnostic imaging
• CT
• Non-contrast : homogeneous hyperdense midline mass within the posterior
fossa
• Contrast : homogeneous enhancement
• Peritumoral edema and hydrocephalus
• Minimal : Calcification, necrosis, cystic degeneration, and hemorrhage
15. Diagnostic imaging
• MRI
• Brain and spine
• Early post operative MRI : residual tumor
• T1 : hypointense to isointense
• T2 : isointense to hyperintense
• T1 c Gd : typically robust but may appear homogeneous or slightly
heterogeneous
• DWI : restricted diffusion
17. Prognosis
• Average-risk patients
• Children 3 years and older
• Without evidence of gross or microscopic metastatic disease at diagnosis
• And with less than 1.5 cm2 of residual tumor after surgical resection
• High-risk patients
• younger than 3 years or any patient
• With evidence of metastatic tumor spread
• Or significant residual tumor (>1.5 cm2) after surgery
19. Surgery
• Goal
• obtaining a tissue diagnosis
• achieving maximal safe tumor resection
• relieving critical structures from mass effect
• addressing any associated hydrocephalus
20. Symptomatic hydrocephalus
• Decision must be made whether to treat the hydrocephalus
beforehand or at the time of tumor resection
• Temporary CSF diversion : external ventricular drain (EVD), diversion
through a ventriculoperitoneal shunt (VPS), diversion via endoscopic
third ventriculostomy (ETV)
• 10-40% require permanent CSF diversion after resection of the tumor
• Factor
• more severe hydrocephalus at diagnosis
• younger patient age
• larger preoperative tumor size
21. Surgery
• Midline suboccipital approach
• Inferior telovelar approach
• If an EVD was placed : gradual weaning
• MRI is performed within 48 hours postoperatively : Significant
residual tumor (>1.5 cm2) should prompt consideration of early
repeat resection
• Unless the procedure was stopped early because of problems with
hemostasis or invasion of tumor into critical structures
22. Postoperative complications
• Cranial nerve palsies, ataxia, dysmetria, or bulbar symptoms : If
potential for recovery, it typically occurs within 6 months after
surgery
• Infection, aseptic meningitis, CSF leak, pseudomeningocele, and
persistent hydrocephalus.
• Cerebellar mutism
23. Cerebellar mutism
• unique postoperative complication seen in children after resection of a
posterior fossa mass lesion
• result from splitting of the vermis and exertion of pressure on the medial
cerebellum
• 10% to 25%
• 1 to 2 days after surgery
• Mutism and ataxia are typically the most significant symptoms
• Emotional lability, hypotonia
• Resolving week to month
• Improvements in affect and oral intake ability occur before resolution of
the speech difficulties
24. Radiation
• Craniospinal irradiation (CSI)
• Average-risk patient and High-risk patients
• Highly radiosensitive
• Short-term side effects
• hair loss, fatigue, weakness, nausea, and vomiting
• Long-term adverse effects
• Neurologic, cognitive, and endocrine abnormalities
• Hypothalamic-pituitary axis dysfunction secondary to CSI may result in
obesity, hypothyroidism, precocious puberty, and growth retardation
• Short stature or scoliosis (or both)
25. Chemotherapy
• Adjuvant chemotherapy
• Average-risk patient and High-risk patients
• Moderate chemosensitive
• No standard regimen
• Lomustine(CCNU), Cisplatin, Vincristine(VCR)
26. Chemotherapy
• Platinum based agent : SNHL
• Alkylating agent : acute myelogenous leukemia
• Complication
• Myelocompression
• Fatigue,nausea,vomiting,loss of apetite,stomatitis, infection
• Nephrotoxicity,hepatotoxicity,cardiomyopathy,urinary bladder and pulmonary
fibrosis
27. Surveillance imaging and disease recurrence
• After resection,postopeararive MRI within 48 hr
• accurately assess the degree of residual disease
• baseline for assessing response to subsequent adjuvant therapy
• disease recurrence on follow-up imaging studies
• Long-term follow-up imaging
• repeat MRI every 3 to 6 months for the first 2 years after treatment
• Surveillance imaging has not been shown to detect a significant proportion of
asymptomatic disease recurrence in some studies
28. Surveillance imaging and disease recurrence
• Recurrence at the primary site is most common
• Metastasis outside the nervous system is uncommon
• Despite adjuvant treatment, up to 60% of patients will display evidence of
disseminated disease at relapse
• Patients with recurrent disease who were initially treated with adjuvant
radiation therapy and chemotherapy : salvage therapy with either repeat
chemotherapy or focal stereotactic radiotherapy (or both)
• Patients treated initially with surgery and chemotherapy alone, long-term
disease control after local recurrence: salvage high-dose chemotherapy
followed by autologous stem cell rescue combined with radiotherapy
29. Surveillance imaging and disease recurrence
• Collins’ law
• Period of risk of recurrence(PRR)
• Age at diagnosis plus 9 month
• Patients that remain free of recurrence beyond the PRR have a much lower
risk of recurrence
Editor's Notes
Hematoxylin and eosin
Midline splitting the superior cerebellar vermis or superior medullary velum
Telo velar : opening the tela choroidea and inferior medullary velum, the two thin sheets of tissue that form the lower half of the roof of the fourth ventricle, without incising or removing part of the cerebellum
