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Hemihyperplasia (also known as hemihypertrophy) is a congenital condition characterized by asymmetric overgrowth of one or more regions of the body, typically affecting one side of the body (right or left).
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It can be isolated (idiopathic) or occur as part of a genetic syndrome—notably Beckwith–Wiedemann syndrome (BWS), PIK3CA-related overgrowth spectrum (PROS), and Proteus syndrome. Because of its association with embryonal tumors, particularly Wilms tumor, tumor surveillance is essential.
Terminology
| Term | Description |
|---|---|
| Hemihyperplasia | Increase in number of cells, resulting in tissue overgrowth |
| Hemihypertrophy | Increase in cell size (less accurate histologically) |
| Preferred term | Hemihyperplasia is more accurate and now widely used |
| Type | Description |
|---|---|
| Isolated hemihyperplasia (IHH) | No other anomalies or syndromic features |
| Syndromic hemihyperplasia | Occurs with other genetic syndromes (e.g., BWS, Proteus, SGBS, PROS) |
| Segmental | Localized overgrowth (e.g., one limb, face, or portion of trunk) |
| Generalized | Entire side of the body enlarged (rare) |
| Complex | Involvement of multiple tissues (bone, soft tissue, vascular) |
| Feature | Description |
|---|---|
| Onset | Typically present at birth or noted in early infancy |
| Affected areas | One or more of limbs, face, chest wall, abdomen |
| Growth pattern | Asymmetric growth that may persist or worsen with time |
| Associated findings | May include skin thickening, enlarged digits, or asymmetric organ size |
| Functional issues | Limb length discrepancy, scoliosis, gait abnormalities |
Syndromes associated with hemihyperplasia:
| Syndrome | Distinguishing Features |
|---|---|
| Beckwith–Wiedemann syndrome (BWS) | Macroglossia, omphalocele, organomegaly, neonatal hypoglycemia |
| ‣ | Segmental overgrowth, vascular malformations, lipomatous changes |
| ‣ | Progressive, disproportionate overgrowth; cerebriform nevi, skeletal dysplasia |
| Simpson–Golabi–Behmel syndrome | Coarse facial features, organomegaly, polydactyly |
| ‣ | Overgrowth with café-au-lait macules and neurofibromas |
| ‣ | Capillary malformations, venous/lymphatic anomalies, limb overgrowth |
| Modality | Imaging features |
|---|---|
| US | • First-line for tumor surveillance (kidneys, liver) |
| • May show nephromegaly or liver asymmetry | |
| MR | • Limbs: Quantifies muscle, fat, bone differences |
| • Brain: Considered in facial hemihyperplasia (exclude structural malformations, hemimegalencephaly) | |
| • Abdomen: Tumor detection or confirmation of US findings | |
| Skeletal survey | • Long bone length discrepancies |
| • Hemimegalencephaly (in cerebral overgrowth cases) |
Tumor risk and surveillance:
| Risk | Details |
|---|---|
| Increased tumor risk | Especially Wilms tumor, hepatoblastoma (5–10% risk) |
| Highest risk period | First 8 years of life |
| Surveillance protocol | • Abdominal ultrasound every 3 months until age 7–8 |
| • Serum alpha-fetoprotein (AFP) every 2–3 months (if hepatoblastoma risk suspected) |
| Condition | Differentiating Features |
|---|---|
| Lipomatosis | Fatty overgrowth without skeletal involvement |
| Vascular malformations | Overgrowth often due to venous/lymphatic anomaly (e.g., Klippel–Trénaunay) |
| Muscular hypertrophy | Focal and activity-related |
| Congenital hemihypoplasia | Underdevelopment rather than overgrowth |
| ‣ | Enlarged cerebral hemisphere; may cause seizures, developmental delay |