Cryptorchidism: Reproductive System Physiology - Long Answer

Definition

Embryology and Normal Testicular Descent

Origin of the Testis

• At ~32 days postovulation, gonads arise as thickenings on the medial aspect of the urogenital ridge (posterior abdominal wall)
• The SRY gene (sex-determining region, Y chromosome) triggers testicular differentiation - it activates SOX9, which drives Sertoli cell specification
• By 6-8 weeks, primordial germ cells (PGCs) migrate from the yolk sac and localize within forming testicular cords
• Leydig cells appear in the interstitium by weeks 8-10 and begin testosterone secretion under hCG stimulation

Two Phases of Testicular Descent

• The testes migrate from the posterior abdominal wall to the lower abdomen/pelvic brim
• Controlled by Müllerian-inhibiting substance (MIS)/Anti-Müllerian Hormone (AMH) secreted by Sertoli cells
• The gubernaculum (a fibromuscular band) swells and anchors the testis to the inguinal region, while the cranial suspensory ligament regresses
• INSL3 (insulin-like factor 3, produced by Leydig cells) acting via its receptor RXFP2/LGRF8 is critical for gubernacular swelling and anchoring in this phase

• The testis passes through the inguinal canal into the scrotum
• This phase is androgen-dependent - testosterone (converted to DHT) acts via the androgen receptor
• Androgens are required to induce regression of the cranial suspensory ligament and drive gubernacular elongation/migration
• The genitofemoral nerve (GFN) provides essential innervation to the gubernaculum; calcitonin gene-related peptide (CGRP) released from GFN is the downstream mediator
• Complete descent into the scrotum is not achieved until the third trimester

Key hormonal regulators: INSL3 (Phase 1) + Androgens/DHT (Phase 2)

Epidemiology

Classification

• Testis arrested along its normal path of descent
• Locations in order of frequency (see figure below):
  1. Inguinal canal (most common, ~70%)
  2. Just inside the deep inguinal ring
  3. Just outside the superficial inguinal ring
  4. High scrotal

• Testis has deviated from the normal path of descent after exiting the inguinal canal
• Sites: superficial inguinal pouch (most common), perineum, root of penis (pubic type), femoral triangle
• Due to rupture/dominance of an accessory tail of the gubernaculum (Lockwood's five tails: scrotal, pubic, perineal, inguinal, femoral)
• An ectopic testis is usually well-developed (unlike an undescended testis, which is small and atrophied)

• A normally descended testis that retracts into the inguinal canal due to hyperactive cremasteric reflex
• Can be manually brought into the scrotum - does NOT require surgery

Fig. Possible sites of cryptorchid (A) and ectopic (B) testes. (The Developing Human, Moore & Persaud)

Pathophysiology and Consequences

Why the Scrotum Matters - Thermoregulation

• Pampiniform plexus (countercurrent heat exchange)
• Cremaster muscle (temperature-regulated elevation/lowering)
• Dartos muscle and thin scrotal skin

Histological Changes (Robbins, Cotran & Kumar)

Notably, similar histologic changes may appear in the contralateral normally descended testis in unilateral cryptorchidism - suggesting an underlying intrinsic gonadal developmental defect (testicular dysgenesis syndrome) rather than purely positional damage.

Etiology and Risk Factors

• Deficiency of fetal testosterone or DHT production
• Deficiency of INSL3 or RXFP2 mutations
• Deficiency of AMH/MIS

• Prader-Willi syndrome
• Noonan syndrome
• Androgen insensitivity syndromes
• HOX gene mutations

• Endocrine disruptors (estrogen-like compounds in the intrauterine environment)
• Twin studies suggest both maternal inheritance and intrauterine environment play roles

Clinical Features

• Asymptomatic - usually discovered by parent or physician noting an empty scrotum
• Unilateral > bilateral
• The undescended testis is smaller and less developed than the contralateral testis

Reproductive Prognosis

• Fertility impairment in cryptorchidism is primarily due to Sertoli cell/seminiferous epithelium dysfunction (reflected by low inhibin B), rather than Leydig cell dysfunction (testosterone levels less severely affected)
• Bilateral cryptorchidism carries a significantly worse prognosis for fertility than unilateral

Diagnosis

• Examine in warm room; supine and frog-leg position; palpate inguinal canal and scrotum
• Palpable vs non-palpable testis guides management

• Ultrasound - for inguinal testes
• MRI - for suspected intra-abdominal testis
• Laparoscopy - gold standard for non-palpable testis (diagnostic and therapeutic)
• Hormonal stimulation test (hCG stimulation): rise in testosterone confirms functional testicular tissue; no response suggests absent testes (anorchia)
• FSH, LH, inhibin B - markers of Sertoli cell and spermatogenesis status

Treatment

Medical (Hormonal)

• hCG injections (human chorionic gonadotropin) - stimulates Leydig cells to produce testosterone, promoting descent
• GnRH (buserelin) intranasal - less commonly used
• Success rate is modest (~20-30%); not recommended as primary treatment by modern guidelines

Surgical - Orchidopexy (Definitive Treatment)

• Timing: Current recommendation = 6 to 12 months of age (before histologic changes become established)
  • Sabiston: orchidopexy at 6-12 months for palpable inguinal testis
  • Robbins: "hormone injections followed by early orchiopexy at 6-12 months if medical treatment fails"

1. Standard dartos pouch orchidopexy - for palpable inguinal testis; testis brought down and fixed in a sub-dartos pouch in the scrotum
2. Two-stage Fowler-Stephens orchidopexy - for high intraabdominal testis with short vessels:
   • Stage 1: Ligation of testicular vessels (to allow collateral circulation to develop over 6 months)
   • Stage 2: Orchidopexy via collateral blood supply
3. Laparoscopic orchidopexy - increasingly preferred single-stage option for intra-abdominal testis

Outcomes of Orchidopexy

• Reduces (but does not eliminate) risk of malignancy
• Reduces risk of torsion
• Improves fertility outcomes if performed early
• Deficient spermatogenesis still reported in 10-60% even after orchidopexy
• Cancer risk remains elevated even after repositioning (linked to intrinsic testicular dysgenesis)

Relationship to Testicular Cancer

• Cryptorchidism is the most important risk factor for testicular germ cell tumors
• Risk is highest with abdominal cryptorchidism (>intra-canalicular)
• Mechanism: Germ cell neoplasia in situ (GCNIS) - malignant transformation of arrested spermatogonia/gonocytes
• The contralateral descended testis is also at higher risk for malignancy - supporting the testicular dysgenesis theory
• Most common tumor arising: seminoma
• Orchidopexy does NOT eliminate the cancer risk but does allow regular physical examination and earlier detection

Summary Table