Correct Answer: C. Sertoli cell only syndrome
Sertoli cell-only syndrome (SCOS), also called germinal aplasia, is characterized by the presence of only Sertoli cells lining the seminiferous tubules with complete absence of germ cells at all stages of spermatogenesis. On testicular biopsy, the histopathology shows seminiferous tubules lined exclusively by Sertoli cells with no spermatogenic cells, normal Leydig cells in the interstitium, and normal testicular volume. This results in azoospermia (zero sperm count) despite normal or near-normal testosterone levels, as Leydig cells remain functional. The patient presents with primary infertility due to the inability to produce sperm. SCOS accounts for approximately 10–15% of azoospermic men in India. The condition is either idiopathic or associated with genetic mutations (Y chromosome microdeletions in AZF regions). Unlike testicular atrophy, the tubular architecture is preserved; unlike orchitis, there is no inflammatory infiltrate; and unlike neoplasia, there is no abnormal cell proliferation. The biopsy findings—preserved tubular structure with Sertoli cells only—are pathognomonic for SCOS.
Why the other options are wrong
A. Benign testicular neoplasm — Neoplasms (Leydig cell tumors, Sertoli cell tumors) show abnormal cellular proliferation, disorganized architecture, and mitotic activity on biopsy. SCOS shows normal, orderly arrangement of Sertoli cells with no atypia or proliferation. Neoplasms typically present with a palpable mass or elevated tumor markers, not isolated azoospermia with normal testicular volume. B. Orchitis — Orchitis is characterized by inflammatory infiltrate (lymphocytes, plasma cells, neutrophils) within the interstitium and tubules, often with tubular necrosis and edema. SCOS shows no inflammation, normal interstitium, and preserved tubular architecture. Orchitis typically presents with acute pain, swelling, and fever; SCOS is asymptomatic and discovered during infertility workup. D. Testicular atrophy — Atrophy shows shrunken seminiferous tubules with reduced diameter, thickened basement membrane, and variable loss of germ cells (not complete absence). SCOS has normal or near-normal tubular diameter and architecture with selective, complete absence of germ cells only. Atrophy is secondary to prior injury (trauma, infection, torsion); SCOS is a primary developmental disorder.
High-Yield Facts
- Sertoli cell-only syndrome presents with azoospermia but normal/near-normal testosterone and testicular volume due to preserved Leydig cell function.
- Histopathology shows seminiferous tubules lined by Sertoli cells alone with complete absence of germ cells at all stages and no inflammatory infiltrate.
- Y chromosome microdeletions (AZF regions) are the most common genetic cause; idiopathic cases also occur in Indian populations.
- SCOS accounts for 10–15% of azoospermic men and is the most common cause of non-obstructive azoospermia after hypogonadism.
- Testosterone levels are normal or near-normal because Leydig cells are intact; FSH is markedly elevated due to lack of inhibin feedback from germ cells.
- Diagnosis requires testicular biopsy as semen analysis alone cannot differentiate SCOS from obstructive azoospermia; biopsy is the gold standard.
Mnemonics
SCOS = Sertoli Only Sertoli cells Only = Sperm Output zero. Remember: Leydig cells intact (normal testosterone), Sertoli cells present but germ cells absent (azoospermia). SCOS vs Atrophy (Quick Discriminator) SCOS: Normal tubular size, complete germ cell absence. Atrophy: Shrunken tubules, partial germ cell loss. Think: SCOS is selective loss; atrophy is global shrinkage.
NBE Trap
NBE may pair azoospermia with testicular atrophy to trap students who assume all non-obstructive azoospermia involves tubular shrinkage. SCOS is unique because tubular architecture and volume are preserved—only germ cells are absent.
Clinical Pearl
In Indian infertility clinics, SCOS is increasingly recognized as a leading cause of non-obstructive azoospermia. A young man with primary infertility, azoospermia, and normal testicular volume should raise suspicion for SCOS—biopsy confirms diagnosis and rules out obstructive causes, guiding counseling on genetic testing (Y microdeletion) and assisted reproductive options (TESE/ICSI).
_Reference: Robbins Ch. 21 (Male Reproductive System); Harrison Ch. 340 (Disorders of the Testis and Scrotum); OP Ghai Ch. 8 (Infertility)_