Medulloblastoma. Initial approach by cytology.

Authors: Urieliz Cintrón Torres, CT(ASCP), Astris Pérez Nieto, CT(ASCP), Juan Pérez Berenguer, MD.

Institution: Administration of Medical Services of Puerto Rico Laboratory of Pathology and the University of Puerto Rico School of Medicine.

This is the case of a 1-year-old- boy who presented with a posterior fossa mass with leptomeningeal disease. A cerebrospinal fluid (CSF) sample obtained showed aggregates of atypical small cells with irregular hyperchromatic nuclei, nuclear molding, and scant cytoplasm (Photo 1). The tumor was diagnosed as an embryonal tumor with features of a rhabdoid tumor. Negativity for INI1 is compatible with this interpretation (Table 1.)

Photo 1: CSF. Cytology smears showing aggregates of atypical small cells with irregular, hyperchromatic nuclei, nuclear molding, and scant cytoplasm. Presence of few lymphocytes, few monocytes, few neutrophils, and proteinaceous material. Diff Quick x400.
Photo 2: Cell Block. Aggregates of atypical small cells showing irregular hyperchromatic nuclei, nuclear molding, and scant cytoplasm.  H&E x400.

A biopsy was performed, the tumor was resected and diagnosed as Medulloblastoma, classic type, non-WNT/non-SHH activated, WHO grade IV. The immunostains performed at UPR- School of Medicine supported the diagnosis (Table 1).

Photo 3: Brain, resected cerebellar mass. Medulloblastoma, classic type, non-WNT/non-SHH activated, WHO grade IV. H&Ex400
Table 1. Immunostains

Discussion:

Medulloblastomas are the most common central nervous system (CNS) embryonal tumors and the most common high-grade childhood tumors. They account for approximately 15-20% of all pediatric brain tumors [1]. They are located in the cerebellum, which participates in coordination, equilibrium, and movement. Medulloblastoma tends to spread through CSF to other areas around the brain and spinal cord. This tumor rarely spreads to other areas of the body [2]. The cytomorphology of the cells seen in this case showed small blue cells with nuclear molding, hyperchromasia, and high N/C ratio; all of which are characteristic of medulloblastoma [4]. The positive staining for INI1 and reticulin, among other biomarkers, are also characteristics of medulloblastoma (Table 2).

Table 2. Immunostains (Biopsy)

References:

1.Medulloblastoma. The Brain Tumor Charity. Retrieved from https://www.thebraintumourcharity.org/understanding-brain-tumours/types-brain-tumour-children/medulloblastoma/ on February 23rd, 2019.

2. Medulloblastoma. The Mayo Clinic. Retrieved from https://www.mayoclinic.org/es-es/diseases-conditions/medulloblastoma/cdc-20363524 on February 24th, 2019.

3. Stains INI1. Pathology Outlines (2013). Retrieved from 1http://www.pathologyoutlines.com/topic/stainsini1.html on March 14th, 2019.

4. Koss’ Diagnostic Cytology and Its Histopathologic Bases, Fifth Edition. Krane, Jeffrey F. M.D., Ph.D. International Journal of Gynecological Pathology: July 2007 Volume 26 p Issue 3 p1032.

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