Necrotizing Enterocolitis
The morphological picture of severe intestinal involvement has specific manifestations affecting all layers of the intestinal wall.
- Macroscopic appearance: The affected bowel acquires a characteristic brownish discoloration. Multiple hemorrhages are observed, and gas accumulates within the bowel wall. Fibrin deposition on the peritoneal surface is evident within the abdominal cavity.
- Microscopic appearance: Marked edema and areas of hemorrhage predominate in the tissues. Total mucosal necrosis develops and progressively extends deep into the muscular layer. Inflammatory cellular infiltration is virtually absent or extremely mild.
Twin-to-Twin Transfusion Syndrome
Twin-to-twin transfusion syndrome (TTTS) is a severe complication occurring in multiple gestations. Most frequently diagnosed in monochorionic diamniotic twins, it is significantly less common in monochorionic monoamniotic twins.
Pathogenesis The condition is driven by the formation of deep vascular anastomoses (arteriovenous shunts) within a shared placenta. Blood flow is redistributed such that arterial blood enters a placental cotyledon of one twin, while venous drainage flows into the vascular bed of the co-twin. This unidirectional blood shunting creates two distinct clinical roles:
- Donor twin: Suffers from hypoperfusion. Develops severe anemia, intrauterine growth restriction (IUGR), and oligohydramnios (decreased amniotic fluid volume).
- Recipient twin: Receives an excess blood volume, leading to hypervolemia, polycythemia, compensatory myocardial hypertrophy, massive edema, and polyhydramnios.
This complication is characterized by marked discordance in body weight, dimensions, and hemoglobin levels between the fetuses. The prognosis is extremely poor, accompanied by high perinatal mortality, with donor twins typically dying in utero first.
Non-Immune Hydrops Fetalis
This is a heterogeneous group of severe conditions whose main clinical manifestation is generalized fetal edema not associated with an immunologic incompatibility (such as Rh or ABO blood group incompatibility). Morphological changes in organs and tissues depend entirely on the primary etiology.
Major Etiologic Categories:
- Increased cardiac output: Occurs in twin-to-twin transfusion syndrome, placental chorioangioma, truncus arteriosus, cavernous hemangioma, or fetal hyperthyroidism.
- Severe fetal anemia: May result from β-glucuronidase deficiency, congenital leukemia, hemoglobinopathies, hemolytic anemia, parvovirus B19 infection, intraventricular hemorrhage, massive fetomaternal hemorrhage, or glucose-6-phosphate dehydrogenase (G6PD) deficiency.
- Infectious agents: Toxoplasmosis, rubella, cytomegalovirus (CMV), herpes simplex virus (HSV), syphilis, adenovirus.
- Genetic and chromosomal abnormalities: Trisomies (21, 18, 13), Turner syndrome, triploidy, Noonan syndrome, various skeletal dysplasias, congenital arthrogryposis, and multiple pterygium syndrome.
- Vascular anomalies and compression: Congenital pulmonary airway malformation (CPAM), diaphragmatic hernia, mediastinal teratoma, premature closure of the ductus arteriosus, absence of the ductus venosus, renal vein thrombosis.
- Lymphatic obstruction: Cystic hygroma or decreased fetal motility (e.g., secondary to congenital muscular dystrophy).
- Storage disorders (metabolic): Gaucher disease, Tay-Sachs disease, Niemann-Pick disease, mucopolysaccharidoses / mucolipidosis type I.
Inborn Errors of Metabolism
Inborn errors of metabolism comprise a vast group (over 400 disorders) of genetically determined conditions characterized by disrupted biochemical pathways. These diseases feature a wide spectrum of clinical manifestations, variable ages of onset, and diverse morphologies.
The vast majority of these disorders are inherited in an autosomal recessive pattern, with X-linked forms being significantly less common. The underlying mechanism is a qualitative or quantitative genetic defect in specific enzymes (cytoplasmic, lysosomal, peroxisomal) or transport proteins.
Cellular Damage Mechanisms:
- Pathologic accumulation of precursor substrates.
- Toxic effects of intermediate metabolites.
- Acute deficiency of the biochemical reaction's end product.
Disorders characterized by massive intracellular accumulation of uncleaved metabolic products in various tissues are termed storage diseases (thesaurismoses). Clinically, they are typically divided into groups with predominant central nervous system involvement, hepatocellular disorders, myopathies, and nephropathies. However, certain conditions (homocystinuria, familial hypercholesterolemia, Lesch-Nyhan syndrome) exhibit unique phenotypes that defy this strict categorization.
Phenylketonuria: Pathogenesis and Clinical Features
Phenylketonuria (PKU) is a severe autosomal recessive disorder caused by a major disruption in the metabolism of the essential amino acid phenylalanine. Early newborn screening and timely initiation of dietary therapy are crucial for the child's prognosis and development.
Etiology and Pathogenesis: The primary cause of classic PKU is a congenital deficiency of the enzyme phenylalanine hydroxylase. Atypical forms (up to 10% of cases) also occur, associated with deficiencies in co-factor recycling enzymes, such as dihydropteridine reductase. Due to this enzymatic block, the normal conversion of phenylalanine to tyrosine is impaired. Phenylalanine and its deamination products (phenylpyruvate, phenyllactate, and phenylacetate) rapidly accumulate in the blood, urine, and sweat. These metabolites exert marked neurotoxic effects on the developing central nervous system.
Clinical Manifestations: Infants appear completely healthy at birth. Manifestation begins shortly after the first protein feedings containing phenylalanine (such as breast milk or standard formula). Progressive neurological symptoms develop, peaking by 3 years of age.
Three main groups of symptoms are distinguished:
- Intellectual disability (ranging from moderate impairment to profound disability).
- Severe neurological manifestations: Muscle hypertonia, pronounced tremor, ataxia, various movement disorders, and epileptic seizures.
- Hypopigmentation: Results from impaired melanin synthesis (due to the blocked conversion of phenylalanine to tyrosine). Affected children exhibit a characteristic phenotype: very fair hair, pale skin, and blue eyes. Their skin has increased sensitivity to ultraviolet radiation and is prone to severe dermatitis and eczema.