Kallmann syndrome (KS) is a rare genetic disorder characterized by hypogonadotropic hypogonadism and anosmia or hyposmia. First described in 1856 and recognized as hereditary in 1944, it is also called olfactogenital dysplasia. KS results from defective migration of GnRH neurons from the olfactory placode to the hypothalamus, causing reduced GnRH, low FSH and LH, and sex steroid deficiency. Mutations in KAL-1 and FGFR1 are most common, though over 30 genes are implicated. While MRI typically shows hypoplastic or absent olfactory bulbs, some patients have structurally normal bulbs despite anosmia. KS may be associated with renal agenesis, cryptorchidism, cleft palate, color blindness, sensorineural deafness, and neurological abnormalities. The prevalence is estimated at 1 in 4,000–10,000, with a male predominance of 3:1.

A 20-year-old male with absent puberty and lifelong anosmia underwent clinical assessment, hormonal testing (testosterone, LH, FSH, prolactin, TSH, FT4), karyotyping, semen analysis, and imaging (abdominal/scrotal US,, brain MRI). He was treated with intramuscular testosterone decanoate, with follow-up monitoring of hormones and secondary sexual characteristics.

Case Presentation: A 20-year-old male presented with absent pubertal development and lifelong anosmia. Examination revealed eunuchoid body habitus, micropenis, small testes, Tanner stage I genitalia, gynecomastia, and absent axillary/facial hair. Hormonal evaluation showed low testosterone (30.2 ng/dL), suppressed LH (0.24 mIU/mL), and low-normal FSH (1.68 mIU/mL), with normal prolactin, TSH, and FT4. Semen analysis revealed azoospermia, and karyotype was 46,XY. Abdominal ultrasound was unremarkable; scrotal ultrasound showed bilateral testicular atrophy with hypoechogenicity, microcalcifications, and reduced vascularity. Brain MRI demonstrated a normal hypothalamic–pituitary axis and morphologically intact olfactory bulbs despite anosmia. Treatment and Follow-Up: Treated with intramuscular testosterone decanoate (250 mg/mL), serum testosterone rose to 289 ng/dL with partial pubertal development and improved secondary sexual characteristics.

Kallmann syndrome usually features hypoplastic or absent olfactory bulbs, but normal-appearing bulbs do not exclude the diagnosis. Functional anosmia may occur despite intact morphology due to subtle microstructural defects or genetic heterogeneity (e.g., PROKR2, CHD7 mutations). This case highlights the importance of correlating clinical signs and hormonal findings rather than relying solely on imaging for diagnosis. Early testosterone therapy can induce secondary sexual characteristics and partially normalize endocrine function, while fertility may require additional interventions. Awareness of such atypical presentations is essential to avoid delayed diagnosis and optimize patient outcomes.