Cryptorchidism (Undescended Testis)

Definition

Embryology & Pathogenesis

• In the 5th–6th week of embryological life, gonads arise from the urogenital ridge on the posterior abdominal wall.
• In the 7th–8th months, the testis descends along the inguinal canal into the scrotum, dragging the processus vaginalis with it.
• Key regulatory molecules include INSL3 (insulin-like factor 3), RXFP2/LGRF8, AMH (anti-Müllerian hormone), and HOX gene family receptors (HOX10).
• Androgens are required in the 4th month to induce regression of the cranial suspensory ligament.
• Failure of any of these steps results in cryptorchidism.

Epidemiology

• Unilateral cryptorchidism is ~twice as common as bilateral.
• A pattern of maternal inheritance is noted, but the intrauterine environment also plays a role. — Campbell-Walsh-Wein Urology

Classification

Clinical Presentation & Examination

• Inspection: hypoplastic or poorly rugated scrotum on the affected side.
• Palpation technique (child should be warm and relaxed):
  1. Ask caregivers if the testis is ever visible in the scrotum during a warm bath or sleep (supports retractile testis).
  2. Examine supine; have the child cross their legs or sit cross-legged to dampen the cremasteric reflex.
  3. Apply soap to the inguinal canal and use one hand above the canal to "milk" the testis downward.
  4. If the testis reaches the scrotum and stays there, it is retractile — not undescended.
  5. If the testis is impalpable, consider abdominal location or congenital absence.

Complications

Investigations

• Ultrasound: Generally not recommended for routine cryptorchidism — poor sensitivity for localizing an undescended testis and does not alter surgical management. Exception: obese child where identifying an inguinal testis on US simplifies surgical approach.
• MRI/Laparoscopy: Preferred for non-palpable testes; laparoscopy is the procedure of choice for locating and treating abdominal testes.
• Hormonal evaluation: Indicated when bilateral undescended testes are combined with micropenis (to rule out hypogonadism and disorders of sex development).

Management

Timing

• Observe for the first 6 postnatal months — spontaneous descent may occur.
• If no descent by 6 months, surgery should be performed before 12 months (corrected gestational age).
• Rationale: spontaneous descent is unlikely after 2–6 months in full-term males; early orchidopexy restores testicular growth and preserves spermatogonia. — Campbell-Walsh-Wein Urology

Hormonal Therapy

• hCG (chorionic gonadotropin): May occasionally stimulate descent in bilateral cases where hormonal insufficiency is suspected. If no descent after ~1 month, proceed to surgery.
• GnRH: Has been used for germ cell maturation as an adjunct.
• Current AUA and most modern guidelines do not recommend hormonal therapy as primary treatment — surgery is the treatment of choice. — Campbell-Walsh-Wein Urology; Schwartz's

Surgical: Orchidopexy

• Standard inguinal orchidopexy through a groin + scrotal incision — mobilize the spermatic cord and secure the testis in a subdartos pouch.

• Diagnostic laparoscopy first to confirm location.
• Single-stage laparoscopic orchidopexy if cord length is adequate.
• Two-stage Fowler-Stephens orchidopexy if the testis is too high:
  • Stage 1: Clip the testicular vessels laparoscopically to allow collateral development via the vas deferens (months of waiting).
  • Stage 2: Mobilize the testis with a swath of peritoneum carrying the vas collaterals; success rate >90%.
• Orchiectomy: For postpubertal patients with a small, dysgenetic, or poorly viable testis.

Post-pubertal undescended testis

Prognosis

• Unilateral cryptorchidism treated with childhood orchidopexy: paternity rate ~96% (comparable to controls); inhibin B ~2/3 of normal.
• Bilateral cryptorchidism: paternity rate ~70%; inhibin B ~1/3 of normal; sperm density consistently lower.
• Fertility impairment primarily reflects seminiferous epithelium dysfunction, not Leydig cell (testosterone) failure.
• Malignancy risk persists post-orchidopexy but is reduced; scrotal location allows self-examination for early detection. — Campbell-Walsh-Wein Urology

The Growth Plate (Physis / Epiphyseal Plate)

Definition & Location

Active growth plate: 1 = Reserve zone, 2 = Zone of proliferation, 3 = Zone of hypertrophy, 4 = Zone of mineralization, 5 = Primary spongiosa — Robbins & Cotran Pathologic Basis of Disease

Embryology & Formation

1. A mesenchymal cartilage anlage (mold) forms at ~8 weeks gestation.
2. A primary ossification center appears in the diaphysis — osteoblasts deposit cortex under the periosteum.
3. Secondary ossification centers form in the epiphyses after birth.
4. Plates of cartilage become entrapped between the two expanding ossification centers → forming the growth plate (physis).

Zones of the Growth Plate

Key principle: The thickness of the epiphyseal plate remains constant during growth — the rate of new cartilage production (proliferation zone) equals the rate of resorption. Actual bone lengthening occurs because new matrix production pushes the epiphysis away from the diaphysis. — Histology: A Text and Atlas, Wheater's

Hormonal & Molecular Regulators

Blood Supply

• Epiphyseal vessels (from the secondary ossification center) supply the reserve and proliferative zones.
• Metaphyseal vessels supply the zone of resorption/primary spongiosa.
• The hypertrophic zone is relatively avascular and relies on diffusion — making it the weakest zone and the most common site of physeal fracture.

Epiphyseal Closure

• When maximal growth is achieved, chondrocyte proliferation ceases.
• Remaining cartilage completes its cycle (hypertrophy → calcification → ossification).
• Epiphyseal and diaphyseal marrow cavities become confluent.
• A dense epiphyseal line (seen on X-ray) marks the former growth plate site.
• Timing is governed by estrogen (hence women close earlier than men) and thyroid/GH.
• "Bone age" is assessed radiographically by the appearance and fusion of ossification centers. — Schwartz's Principles of Surgery, 11th Ed.

Growth Plate Injuries — Salter-Harris Classification

In children, a physeal fracture should be assumed until proven otherwise — children rarely get sprains. — Miller's Review of Orthopaedics, 9th Ed.

Zones of the growth plate and classification of injuries — Schwartz's Principles of Surgery

Complications of Growth Plate Injury

Fixation principle: If hardware must cross the physis, use only smooth K-wires — never threaded screws across an open plate. — Schwartz's Principles of Surgery, 11th Ed.