summary Hemihypertrophy is an idiopathic condition that can also be caused by a variety of syndromes, and presents with asymmetry between the right and left sides of the body to a greater degree than can be attributed to normal variation. Diagnosis is made clinically with abnormal asymmetry defined as a 5% or greater difference in length and/or circumference. Treatment is observation with or without shoe lifts for leg length differences < 2 cm at skeletal maturity. Surgical intervention is indicated for leg length differences > 2 cm, with different techniques depending on the discrepancy magnitude and remaining skeletal growth. Epidemiology Incidence varies from 1:14,000 to 1:86,000 Demographics male:female = 2:3 Anatomic location slightly more common on the right side may also involve head, trunk and internal organs Etiology Pathophysiology most common causes are idiopathic (non-syndromic) syndromic neurofibromatosis Beckwith-Wiedemann syndrome Klippel-Trenauney syndrome Proteus syndrome Associated conditions orthopaedic manifestations scoliosis (compensatory) peripheral nerve entrapment (rare) medical conditions & comorbidities malignant intra-abdominal tumors Wilm's tumor (most common) perform serial abdominal ultrasounds (every 3 months) until age 7 to rule out Wilm's tumor then physical exam every 6 months until skeletal maturity adrenal carcinoma hepatoblastoma genitourinary abnormalities medullary sponge kidneys polycystic kidney inguinal hernias Classification Congenital classification congenital total involvement of all organ systems limited only muscular, vascular, skeletal, or neurologic involvement classic (ipsilateral upper and lower limbs) segmental (a single limb) facial crossed acquired very rare can result from injury, infection, radiation or inflammation Syndromic classification non-syndromic (isolated) syndromic (part of a clinical syndrome) Presentation Physical exam findings rarely apparent at birth, manifest during growth skin often thicker on involved side more hair on corresponding side of the head limb circumference asymmetric leg-length discrepancy (LLD) Imaging Radiographs AP + lateral of affected limb may demonstrate enlargement of bone and soft tissue osseous maturation may be seen Abdominal ultrasound indications perform serial abdominal ultrasounds (every 3 months) until age 7 to rule out Wilm's tumor Studies Renal function tests Serum alpha-fetoprotein screen for embryonal tumors Treatment Nonoperative observation, shoelift, corrective shoes indications < 2 cm projected LLD at maturity Operative surgical correction indications based on principles of leg length discrepancies