What is the cause of a 21-day-old male baby's right testis being palpable in the inguinal canal, small in size, and easily movable to the scrotum, while the left testis is normal?

Diagnosis: Retractile Testis

This 21-day-old infant has a retractile testis, not an undescended testis, because the right testis is palpable in the inguinal canal, small in size, and can be easily manipulated into the scrotum. 1

Key Distinguishing Features

The critical diagnostic feature here is that the testis "easily moved to scrotum" - this defines a retractile testis rather than true cryptorchidism. 1

Retractile Testis Characteristics:

• Testis can be manipulated easily into the scrotum and remains there without traction until the cremasteric reflex is induced 2
• Most commonly occurs in boys between 5-6 years of age, though can present earlier 3
• Represents a hyperactive cremasteric reflex pulling the testis upward 1
• The testis is palpable (not truly undescended) 1

Why This is NOT Undescended Testis (Cryptorchidism):

• True undescended testes cannot be easily manipulated into the scrotum or do not remain there 1
• In cryptorchidism, the testis is arrested along the path of descent and requires surgical intervention 1, 4

Why This is NOT Ectopic Testis:

• Ectopic testes are located outside the normal path of descent (e.g., superficial inguinal pouch, perineum, femoral region) 3
• This testis is in the inguinal canal, which is along the normal descent pathway 3

Why This is NOT Testicular Torsion:

• No acute presentation described 5
• Testis is easily mobile without pain or vascular compromise 5

Management Approach

Annual monitoring is required because retractile testes carry a 32% risk of becoming truly undescended (ascending testis) during childhood. 1, 2

Specific Follow-up Protocol:

• Assess testicular position at least annually at well-child visits 1
• Monitor for secondary ascent (testis becoming truly undescended) 1
• Risk of ascent is highest in boys younger than 7 years (79% vs 42% in older boys) 2
• Watch for development of a taut or inelastic spermatic cord, which increases risk of ascent to 56% 2

When to Refer for Surgery:

• If the testis ascends and becomes truly cryptorchid (cannot be manipulated into scrotum) 6, 2
• If testicular size decreases during follow-up 6
• If an associated inguinal hernia is present (68.8% of these cases require surgery) 6

Important Clinical Pitfalls

Do NOT order imaging studies (ultrasound, CT, MRI) - these rarely assist in decision-making and should not be performed prior to specialist referral if concerns arise. 1, 4

Do NOT delay monitoring - 77.3% of retractile testes have spontaneously favorable evolution by age 14, but the 32% that ascend require intervention. 6, 2

Do NOT assume this is benign - one case of testicular carcinoma has been reported in a patient with retractile testis, emphasizing the need for continued surveillance even after apparent descent. 6

Answer: D. Retractile testis