General
- Pituitary blastoma is an exceptionally rare embryonal neoplasm of the sellar region.
- It is composed of three distinct elements: primitive blastemal cells, neuroendocrine cells, and Rathke pouch epithelium.
- A rare embryonal neoplasm of infancy composed of primitive blastemal cells, neuroendocrine cells, and Rathke epithelium, has been added as a tumor type in WHO CNS5.
Definition
- Essential criteria
- The presence of Rathke pouch epithelial glands, primitive blastomatous cells, and folliculostellate anterior pituitary cells.
- Demonstration of DICER1 alterations.
- Desirable criteria
- Diagnosis in children aged under 2 years.
- Clinical presentation of Cushing syndrome.
- A personal or family history of DICER1 syndrome.
Numbers
- It is an exceptionally rare tumour with fewer than 20 published cases.
- It primarily affects infants, usually occurring in children under 2 years of age, with a median age of 9 months.
- There is a slight female predominance.
WHO grade
- No WHO grade
- Is a malignant embryonal neoplasm
Histopathology
Macroscopic
- Descriptions are limited due to rarity, but tumours may show focal cystic or haemorrhagic changes and partial necrosis.
Microscopic
- The tumour displays a triphasic morphology:
- Large neuroendocrine cells in lobules/sheets,
- Cuboidal/columnar primitive Rathke pouch epithelium forming rosettes or glands
- Small undifferentiated blastemal cells.
- Ultrastructurally, it resembles the fetal pituitary gland at 10–12 weeks of gestation.
- Proliferation: The Ki-67 labelling index can be as high as 60%, particularly within the Rathke pouch epithelium.
Immunophenotype
- Neuroendocrine cells: Express ACTH, beta-endorphin, and MSH; growth hormone (GH) is expressed to a lesser extent.
- Rathke pouch epithelium: Shows the strongest expression of EMA and keratins.
- Folliculostellate cells: Stained by S100.
Pathogenesis
- The tumour is fundamentally linked to genetic alterations in DICER1, a gene critical for microRNA processing.
- Most cases involve a germline loss-of-function variant on one allele coupled with a somatic RNase IIIb hotspot mutation on the other.
Localisation
- It originates within the sellar region, frequently extending into the suprasellar region and potentially invading the cavernous sinus.
Clinical features
- Cushing syndrome is one of the most common presentations due to the overexpression of ACTH by tumour cells.
- Ophthalmoplegia (paralysis of eye muscles) may occur due to parasellar extension.
- Diabetes insipidus is also a reported clinical feature.
Radiological features
- On MRI, these are typically well-demarcated sellar masses.
- They may appear partially cystic or haemorrhagic.
Management
- Management involves a comprehensive endocrine evaluation (particularly ACTH levels) and ophthalmological checks.
- Genetic counselling and germline sequencing of DICER1 are recommended for the patient and family.
- Liu 2021:
- Surgical resection is the primary management approach and can provide long-term disease control for some patients with pituitary blastoma.
- Long-term neuroendocrine management is essential for quality survival after surgical intervention.
- Genetic testing for DICER1 mutations should be performed as pituitary blastoma is strongly associated with germline DICER1 mutations.
- Adjuvant therapy (chemotherapy or radiotherapy) is not consistently associated with improved survival, but may be considered on a case-by-case basis depending on tumor recurrence or residual disease.
- Multidisciplinary care involving neurosurgery, pediatric oncology, and endocrinology is recommended for optimal management and surveillance.
Prognosis
- Prognostic factors are not fully understood due to the rarity of the condition.
- Mortality is significant; in a series of 13 patients, 38% died, primarily from treatment-related complications or tumour progression.
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