Medulloblastoma pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Haytham Allaham, M.D. [2] Associate Editor(s)-in-Chief: Syed Musadiq Ali M.B.B.S.[3]


Medulloblastoma arises from the cerebellar stem cells, which are normally involved in the anatomical development of the cerebellum and posterior cranial fossa structures. Medulloblastoma is an invasive and rapidly growing brain tumor which may metastasize to different organs of the body. Genes involved in the pathogenesis of medulloblastoma include CTNNB1 gene, PTCH1 gene, MLL2 gene, SMARCA4 gene, DDX3X gene, CTDNEP1 gene, KDM6A gene, and TBR1 gene. Medullobastomas are associated with a number of syndromes that include Gorlin syndrome and Turcot syndrome.[1] On gross pathology, a pink, solid, and well circumscribed mass is a characteristic finding of medulloblastoma. On microscopic histopathological analysis, round tumor cells, elevated mitotic rate, increased nucleus:cytoplasmic ratio, and Homer-Wright rosettes are characteristic findings of medulloblastoma.[2]



  • Medulloblastoma may be classified into at least four major subtypes based on a molecular classification system which includes:[7][8][9]
  • WNT subgroup:
  • Present among 10% of medulloblastoma patients
  • Cytogenetic markers include classic monosomy 6
  • Molecular markers include beta-catenin
  • SHH subgroup:
  • Present among 25% of medulloblastoma patients
  • Cytogenetic markers include chromosome 9q deletion
  • Molecular markers include SFRP1 or GAB1
  • Group 3:
  • Present among 30% of medulloblastoma patients
  • Cytogenetic markers include isochromosome 17q
  • Molecular markers include MYC activation
  • Group 4:
  • Present among 35% of medulloblastoma patients
  • Cytogenetic markers include isochromosome 17q
  • Molecular markers are still under investigation

Associated Conditions

  • Medulloblastoma is associated with a number of syndromes that include:[1][10]

Gross Pathology

  • On gross pathology, a pink, solid, and well circumscribed mass is a characteristic finding of medulloblastoma.[1]
  • The following image demonstrates the gross pathology observed in medulloblastoma:

Microscopic Pathology

  • On microscopic histopathological analysis, round tumor cells, elevated mitotic rate, increased nucleus:cytoplasm ratio, and Homer-Wright rosettes are characteristic findings of medulloblastoma.[2][12]
  • Medulloblastoma may be classified into two subtypes based on WHO histological classification system which include classic medulloblastoma and variant medulloblastoma.
  • Variant medulloblastoma may be further classified into desmoplastic medulloblastoma, large cell medulloblastoma, anaplastic​ medulloblastoma, and medulloblastoma with extensive nodularity.[2][10]
  • The table below differentiates between the five main groups of medulloblastoma according to the WHO histological classification system:[13]
Grade Histologic features

Classic medulloblastoma

  • Dense sheet like growth of cells
  • Hyperchromatic round-to-oval nucleus
  • Increased mitotic activity
  • Conspicuous apoptosis
  • Homer-Wright rosettes
  • Necrosis is less common

Desmoplastic medulloblastoma variant

Medulloblastoma with extensive nodularity variant

  • Cellular uniformity
  • Fine fibrillary matrix
  • Occasional presence of mature ganglion cells

Large cell / anaplastic medulloblastoma variant

  • Demonstrate high mitotic activity
  • Pleomorphism
  • Large round nucleus with variable eosinophilic cytoplasm
  • Hemorrhage
  • Necrosis is common

  • Shown below is a series of microscopic images observed in medulloblastoma:


  1. 1.0 1.1 1.2 1.3 1.4 Medulloblastoma. Wikipedia(2015) Accessed on September, 28 2015
  2. 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 Medulloblastoma. Libre Pathology (2015) Accessed on September, 28 2015
  3. Evans G, Burnell L, Campbell R, Gattamaneni HR, Birch J (1993). "Congenital anomalies and genetic syndromes in 173 cases of medulloblastoma". Med. Pediatr. Oncol. 21 (6): 433–4. PMID 8515724.
  4. Kozmik Z, Sure U, Rüedi D, Busslinger M, Aguzzi A (June 1995). "Deregulated expression of PAX5 in medulloblastoma". Proc. Natl. Acad. Sci. U.S.A. 92 (12): 5709–13. doi:10.1073/pnas.92.12.5709. PMC 41766. PMID 7777574.
  5. Yokota N, Aruga J, Takai S, Yamada K, Hamazaki M, Iwase T, Sugimura H, Mikoshiba K (January 1996). "Predominant expression of human zic in cerebellar granule cell lineage and medulloblastoma". Cancer Res. 56 (2): 377–83. PMID 8542595.
  6. Katsetos CD, Liu HM, Zacks SI (October 1988). "Immunohistochemical and ultrastructural observations on Homer Wright (neuroblastic) rosettes and the "pale islands" of human cerebellar medulloblastomas". Hum. Pathol. 19 (10): 1219–27. PMID 3139544.
  7. Northcott PA, Shih DJ, Peacock J, Garzia L, Morrissy AS, Zichner T; et al. (2012). "Subgroup-specific structural variation across 1,000 medulloblastoma genomes". Nature. 488 (7409): 49–56. doi:10.1038/nature11327. PMC 3683624. PMID 22832581.
  8. Leary SE, Olson JM (2012) The molecular classification of medulloblastoma: driving the next generation clinical trials. Curr Opin Pediatr 24 (1):33-9. DOI:10.1097/MOP.0b013e32834ec106 PMID: 22189395
  9. Sure U, Berghorn WJ, Bertalanffy H, Wakabayashi T, Yoshida J, Sugita K, Seeger W (1995). "Staging, scoring and grading of medulloblastoma. A postoperative prognosis predicting system based on the cases of a single institute". Acta Neurochir (Wien). 132 (1–3): 59–65. PMID 7754860.
  10. 10.0 10.1 Medulloblastoma. Radiopaedia(2015) Accessed on September, 28 2015
  11. Evans DG, Farndon PA, Burnell LD, Gattamaneni HR, Birch JM (November 1991). "The incidence of Gorlin syndrome in 173 consecutive cases of medulloblastoma". Br. J. Cancer. 64 (5): 959–61. PMC 1977448. PMID 1931625.
  12. McLendon RE, Friedman HS, Fuchs HE, Kun LE, Bigner SH (February 1999). "Diagnostic markers in paediatric medulloblastoma: a Paediatric Oncology Group Study". Histopathology. 34 (2): 154–62. PMID 10064395.
  13. Louis DN, Ohgaki H, Wiestler OD, Cavenee WK, Burger PC, Jouvet A; et al. (2007). "The 2007 WHO classification of tumours of the central nervous system". Acta Neuropathol. 114 (2): 97–109. doi:10.1007/s00401-007-0243-4. PMC 1929165. PMID 17618441.