CNS tumor
Embryonal tumors
Desmoplastic / nodular medulloblastoma

Author: Nirupama Singh, M.D., Ph.D. (see Authors page)

Revised: 15 September 2017, last major update August 2017

Copyright: (c) 2005-2017, PathologyOutlines.com, Inc.

PubMed search: Desmoplastic [title] medulloblastoma

Related topics: Medulloblastoma

Cite this page: Singh, N. Desmoplastic / nodular medulloblastoma. PathologyOutlines.com website. http://pathologyoutlines.com/topic/cnstumormedulloblastomadesmo.html. Accessed September 22nd, 2017.
Definition / general
  • An embryonal neural tumor arising in the cerebellum
  • Characterized by nodular, reticulin free zones and reticulin rich internodular areas with densely packed, poorly differentiated cells
Essential features
  • Desmoplastic / nodular medulloblastoma occurs in cerebellar hemispheres and the midline (classic medulloblastomas are restricted to midline)
  • Closely related to medulloblastoma with extensive nodularity (MBEN)
  • Similar to other medulloblastomas, it is histologically a WHO grade IV tumor
  • Bimodal age distribution with high incidence in young children and adolescents
Terminology
  • WHO 2016 classifies medulloblastoma as genetically or histologically defined
  • There are are 4 histologically defined medulloblastomas; desmoplastic / nodular medulloblastoma, medulloblastoma with extensive nodularity (MBEN), classic medulloblastoma and large cell / anaplastic medulloblastoma
Epidemiology
  • Bimodal age distribution but most commonly present in children ( < 3 years)
  • In early childhood, it is associated with nevoid basal cell carcinoma syndrome, also known as Gorlin syndrome
Sites
  • Most medulloblastomas are restricted to the midline, but desmoplastic / nodular medulloblastoma may also arise in the cerebellar hemispheres and in the vermis
Diagnosis
  • Two important characteristics are (1) reticulin fibers with densely packed, undifferentiated cells with moderate pleomorphism and (2) reticulin free zones (pale islands)
Radiology description
  • Solid, contrast enhancing mass
Prognostic factors
  • In infants, progression free or overall survival at 8 years was significantly better for desmoplastic variants than other medulloblastomas (J Clin Oncol 2010;28:4961)
Treatment
  • Surgery with chemotherapy has an excellent outcome in early childhood
Spread
  • Tumors can relapse locally or metastasize via cerebrospinal fluid pathways
Microscopic (histologic) description
  • Nodular architecture; tumor is permeated by rich reticulin fibers around the pale nodules, giving a desmoplastic appearance
  • Pale reticulin poor nodules consist of tumor cells with variable neurocytic maturation embedded in a neuropil-like fibrillary matrix
  • Reticulin rich area consists of highly proliferative, undifferentiated cells with hyperchromatic and mild pleomorphic nuclei
  • Mitotic activity is higher in internodular versus nodular areas
Microscopic (histologic) images

Images hosted on PathOut server:

Desmoplastic medulloblastoma images contributed by Nirupama Singh M.D., Ph.D.



Images hosted on other servers:

Round pale tumor nodules with darker tumor cell zones

Reticulin poor fine fibrillary background

Uniform round to oval cells

Dark collagen rich areas with small tumor cells

Reticulin stain

Positive stains
  • Nodules show variable expression of neuronal markers, including synaptophysin and NeuN
  • Ki67 proliferation index is much higher in internodular areas than in nodules
  • Activation of SHH pathway can be inferred by immunohistochemistry for specific targets, such as GAB1 and TNFRSF16, mostly in internodular areas (Acta Neuropathol 2011;121:381)
Molecular / cytogenetics description
  • This variant of medulloblastoma displays pathologic activation of the SHH pathway, which is often caused by mutations of SUFU and PTCH1 in young children versus PTCH1 and SMO mutations in adults (Cancer Cell 2014;25:393)
Differential diagnosis
  • Medulloblastoma with extensive nodularity (MBEN)
Board review question #1
Desmoplastic medulloblastoma is associated with which syndrome?

  1. Cowden disease
  2. Gardner syndrome
  3. Gorlin syndrome
  4. Turcot syndrome
Board review answer #1
C. Gorlin syndrome (medulloblastomas are present in both Gorlin and Turcot syndrome but nodular / desmoplastic medulloblastoma occurs in Gorlin syndrome.)
Board review question #2
The most common site for desmoplastic medulloblastoma is:

  1. Cerebellum
  2. Cerebral hemispheres
  3. Vermis
  4. 4th ventricle
Board review answer #2
A. Cerebellum (compared to other medulloblastomas which occur most commonly at midline, e.g., vermis)