Epidemiology and dysontogenetic theory
Although malignant neoplasms (MNs) in children are much less common than in adults (about 2% of the total burden of oncological diseases), they remain one of the leading causes of childhood mortality. In developed countries, they account for 10% of deaths, placing oncology in second place after accidents.
The foundation of pediatric oncology remains the dysontogenetic theory proposed by Julius Cohnheim back in 1902. According to this theory, tumors form from embryonic cell rests due to impaired normal tissue development. While such tumors are rare in adults, in infants under 1 year of age dysontogenetic neoplasms account for up to 85% of all MNs.
In medical practice, two criteria are still used to define the concept of a "congenital tumor":
- The lesion manifested during the first year of life.
- The lesion was diagnosed at birth and strictly within the first 3 months.
Association with malformations and genetics
The processes of oncogenesis and teratogenesis (malformation formation) in children go hand in hand. On average, 30% of patients with tumors have concomitant developmental anomalies. There are typical clinical patterns:
- Wilms tumor (nephroblastoma) and hepatoblastoma are extremely frequently accompanied by hemihypertrophy — asymmetric enlargement of one half of the body, limbs, or face.
- Central nervous system neoplasms are often combined with brain malformations.
- Gonadal tumors are associated with genital anomalies.
Genetic factors play a colossal role in the development of childhood tumors. Science is aware of more than 100 syndromes with hereditary predisposition. Classic examples of proven hereditary tumors are retinoblastoma, nephroblastoma, and neuroblastoma.
Tumor-like lesions: hamartomas and choristomas
In pediatric pathologic anatomy, it is critically important to distinguish true tumors from malformations, although the boundary between them is often blurred.
Hamartoma (from Greek hamartia — error) is a nodular defect of embryonic development. It consists of the same tissue components as the organ in which it is located, but differs by a chaotic arrangement of cells and impaired differentiation. This is a borderline state between a malformation and a tumor. There is still debate regarding the classification of certain formations: some scientists consider hemangiomas, lymphangiomas, liver adenomas, and cardiac rhabdomyomas to be hamartomas, while others consider them true tumors.
Choristoma is a tumor-like nodule growing from choristia (heterotopia). Choristia (from Greek choristos — separated) represents a patch of completely normally formed tissue that "got lost" during embryogenesis and ended up in an atypical anatomical location.
Benign childhood tumors
In children under 14 years of age, more than 80% of all neoplasms are benign. Fibromas, teratomas, lymphangiomas, and hemangiomas lead the way.
Hemangioma (capillary, cavernous, or mixed) most commonly affects the skin of the head, neck, and trunk. It has a specific dynamic: rapid growth in the first months of life, growth arrest by 1–3 years, and spontaneous involution by 5 years. Upon immunohistochemistry (IHC), such involuting forms show a positive reaction for the endothelial marker GLUT-1. However, progressive variants with infiltrative growth and recurrence also occur.
Special attention should be paid to associated syndromes:
- Kasabach–Merritt syndrome: a severe complication in which consumption coagulopathy (massive thrombosis) develops within a giant hemangioma, leading to thrombocytopenic purpura.
- von Hippel–Lindau syndrome: a hereditary pathology manifested by multiple vascular tumors.
Lymphangioma is usually detected before 3 years of age. Its clinical hazard directly depends on its localization: superficial forms are relatively safe, whereas deep ones (in the axillae, mediastinum, retroperitoneal space, or deep neck zones) pose a serious threat.
Briefly: answers to topical questions
What complications, besides Kasabach–Merritt syndrome, can occur with the development of large hemangiomas in children?
Large hemangiomas in children can lead to ulceration, tumor infection, bleeding, and recurrence.
- Infiltrative growth can lead to tumor recurrence; this is characteristic of progressive hemangiomas that do not undergo involution.
- Ulceration and tumor infection are among the possible complications.
- Bleeding can occur when the tumor ulcerates.
What microscopic components form the classical triad in the histological examination of nephroblastoma?
The histological examination of nephroblastoma describes the following components:
- Epithelial component — contains nephron differentiation structures, less commonly structures resembling renal glomeruli.
- Mesenchymal component — represented by loose immature connective tissue; areas of smooth and striated muscle tissue, adipose tissue, cartilage, and bone may be found within it.
- Blastemal component — may predominate in the structure of metastases.
What specific structures are found upon microscopy of neuroblastoma?
Microscopic examination of neuroblastoma reveals various specific structures depending on the degree of tumor differentiation.
- Solid sheets — continuous accumulations of small lymphocyte-like cells with hyperchromatic nuclei (in poorly differentiated tumors).
- Pseudorosettes — specific structures in the form of a wreath of cells surrounding central eosinophilic accumulations of neurofibrils.
- Eosinophilic neurofibrillary processes — appear in more differentiated tumors.
- Neurosecretory granules and microtubules in the processes — are detected by electron microscopic examination.
From which germ layers do teratomas form in children?
Teratomas form from tissues of all three germ layers; tissues of ectodermal origin predominate. The composition of mature teratomas may include epidermis and its derivatives, glial, neural, adipose, muscular, cartilaginous, and bone tissues, as well as intestinal, respiratory, and thyroid-type structures.
How not to confuse tumor-like lesions: Hamartoma — "Where it should be, but chaotic" (tissue of its own organ, but structure is disrupted). Choristoma — "Good, but foreign" (normal tissue, but in an atypical place).
Class and exam questions
What is the essence of the dysontogenetic theory?
This theory explains the development of tumors in children from embryonic tissue remnants that persisted due to intrauterine organogenesis disorders.
What malformations are associated with hepatoblastoma?
Hepatoblastoma, like Wilms tumor, is often combined with hemihypertrophy — congenital enlargement of one half of the trunk, face, or limbs.
Which immunohistochemical marker is characteristic of juvenile hemangiomas?
Hemangiomas prone to involution are characterized by positive endothelial staining in the reaction with the GLUT-1 antibody.
Why can lymphangiomas be dangerous?
Their danger is due to their localization. The location of lymphangiomas in anatomically complex and deep zones (mediastinum, deep parts of the neck, retroperitoneal space) complicates treatment and can compress vital organs.
What else to study on this topic
- Morphological structure and classification of teratomas in children
- Histological picture of nephroblastoma (Wilms tumor)
- Pathogenesis and developmental stages of retinoblastoma
- Differential diagnosis of capillary and cavernous hemangiomas
- Mechanisms of coagulopathy development in Kasabach–Merritt syndrome
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