Histological structure and anaplasia
The tumor includes two main components:
- Epithelial component: contains nephron differentiation structures, with elements resembling renal corpuscles being less commonly detected.
- Mesenchymal component: formed by loose immature connective tissue with potential heterologous elements (smooth and striated muscle, adipose tissue, cartilage, bone).
The only reliable histological sign of an unfavorable prognosis is anaplasia. Its key criteria include nuclear enlargement, marked nuclear polymorphism, hyperchromasia, and the presence of atypical mitoses. At the same time, the degree of tissue differentiation per se does not affect the prognosis.
Metastasis and clinical course features
The spread of the tumor process occurs via two pathways:
- Lymphogenous pathway: metastases spread to regional collectors of the renal hilum and para-aortic lymph nodes, and further into the mesentery and hepatic hilum.
- Hematogenous pathway: secondary lesions are predominantly found in the lungs. It is worth noting that bone metastasis is atypical for this tumor. The blastemal component predominates in the structure of metastatic lesions.
Pathogenesis and markers
Genetic alterations play a certain role in pathogenesis, including loss of heterozygosity at 11p15.5, trisomies, and p53 gene mutations. The tumor is frequently accompanied by specific laboratory and clinical manifestations:
- A marked elevation in blood alpha-fetoprotein levels is used for diagnosis and monitoring of recurrences.
- Human chorionic gonadotropin production can cause precocious puberty.
- The onset of thrombocytosis is associated with the production of thrombopoietin by tumor cells.
Briefly: answers to topical questions
Where is medulloblastoma typically localized in the brain?
Medulloblastoma typically develops from the roof of the fourth ventricle and grows into the vermis of the nodular-floccular lobe of the cerebellum, located in the posterior cranial fossa. The tumor may involve the superior cerebellar vermis, and in atypical localization, it can be found in the cerebellar hemispheres or the cerebellopontine angle.
Through which pathway does medulloblastoma predominantly metastasize within the central nervous system?
Medulloblastoma metastasis in the central nervous system occurs predominantly via the cerebrospinal fluid pathways to other areas of the brain and spinal cord (neuroaxis). The tumor is capable of leptomeningeal dissemination and the formation of secondary lesions along the CSF pathways.
What are the four main molecular-genetic subgroups of medulloblastoma?
The classification of medulloblastomas distinguishes the following main molecular-genetic subgroups:
- WNT-activated (WNT)
- SHH-activated (SHH)
- non-WNT/non-SHH Group 3 (Group 3)
- non-WNT/non-SHH Group 4 (Group 4)
From which embryonic cells does medulloblastoma originate?
The provided sources indicate that medulloblastoma belongs to embryonic tumors; medulloblasts are named among the cells from which primary brain tumors can develop. It is also noted that medulloblastoma develops from the roof of the fourth ventricle.
Which genetic syndromes increase the risk of developing medulloblastoma?
The development of medulloblastoma is associated with several hereditary syndromes:
- Gorlin syndrome (Gorlin / basal cell naevus syndrome)
- Li-Fraumeni syndrome (Li–Fraumeni)
- Turcot syndrome (Turcot)
- Cowden syndrome (Cowden)
What macroscopic features are characteristic of the medulloblastoma tumor node?
The tumor nodular complex of medulloblastoma is a large space-occupying cerebellar mass that predominantly involves the vermis and lies superficially, posteriorly adhering closely to the pia mater. The structure of the neoplasm may be represented by a macronodular conglomerate or have a mixed solid-cystic architecture.
What are the main histological variants of medulloblastoma distinguished in the WHO classification?
The WHO classification distinguishes the following histologically defined variants of medulloblastoma:
- classic medulloblastoma;
- desmoplastic/nodular medulloblastoma;
- medulloblastoma with extensive nodularity;
- large cell/anaplastic medulloblastoma.
MEMA: Lesion, Anaplasia (nuclear criteria), Metastases (lungs), Alpha-fetoprotein.
Class and exam questions
Which histological feature worsens the prognosis in medulloblastoma?
The only histological criterion for a poor prognosis is the presence of anaplasia, which is characterized by hyperchromasia, enlargement, nuclear polymorphism, and atypical mitoses.
Where do hematogenous metastases most commonly spread?
Hematogenous metastases are found predominantly in the lungs, whereas bone involvement is uncharacteristic of this tumor.
What specific laboratory changes accompany the tumor?
An elevation of blood alpha-fetoprotein levels is noted, as well as the development of thrombocytosis due to thrombopoietin synthesis.
What else to study on this topic
- Nephroblastomatosis and its differentiation from tumor
- Epidemiological indicators of hepatoblastoma
- Genetic anomalies and syndrome associations
- Macroscopic presentation of hepatic localization
- The role of the PAS reaction in microscopic examination
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