Reproductive

Male Reproductive Anatomy

The male reproductive system spans the pelvic prostate and seminal vesicles and the scrotal testes, epididymes, and spermatic cords, evaluated principally with multiparametric prostate MRI and high-resolution scrotal ultrasound. The zonal anatomy of the prostate is central to cancer detection and PI-RADS interpretation, while ultrasound is definitive for scrotal emergencies. Knowledge of ductal pathways and vascular supply informs assessment of infertility, infection, and malignancy.

Key Structures

Prostate zones: peripheral zone (high T2, origin of ~70% of cancers), central zone, transition zone (site of BPH), and anterior fibromuscular stroma
Seminal vesicles: paired grape-like, T2-hyperintense structures posterosuperior to the prostate; join the vas to form ejaculatory ducts
Testes: homogeneous mid-level echotexture on US, intermediate-high T2 on MRI; mediastinum testis as an echogenic band
Epididymis: head (globus major) at the superior pole, body, and tail; slightly more heterogeneous than the testis
Vas deferens and spermatic cord: cord contains the vas, testicular artery, and pampiniform venous plexus traversing the inguinal canal
Penis: paired corpora cavernosa and the corpus spongiosum enclosing the urethra, bound by the tunica albuginea and Buck fascia
Neurovascular bundles posterolateral to the prostate—a route of extracapsular tumor spread

Imaging Planes & Modalities

Multiparametric prostate MRI (high-resolution T2, DWI with high b-value/ADC, and dynamic contrast) detects and stages cancer using PI-RADS; T2 and DWI are dominant sequences
High-frequency scrotal ultrasound with color and spectral Doppler is first-line for pain, masses, and torsion, assessing echotexture and vascularity
Axial, coronal, and sagittal T2 aligned to the prostate optimize zonal and capsular assessment and seminal-vesicle invasion
Transrectal ultrasound guides prostate biopsy (often MRI/US fusion) and assesses prostate volume
MRI of the penis/scrotum characterizes tumors, trauma (tunica rupture), and Peyronie disease
PET/CT (PSMA) stages nodal and metastatic prostate cancer beyond the local MRI assessment

Landmarks & Normal Values

PI-RADS assessment category 1-5 based on the dominant sequence (DWI for peripheral zone, T2 for transition zone)
Normal prostate volume ~20-30 mL in young men; PSA density (PSA/volume) aids risk stratification
Normal adult testis ~3-5 cm long, 15-25 mL volume, symmetric echotexture
Testicular artery low-resistance waveform on Doppler; asymmetric absence of flow indicates torsion
Seminal vesicles and the neurovascular bundles define extraprostatic extension landmarks for staging

Anatomical Variants

Undescended testis (cryptorchidism), commonly in the inguinal canal—raises malignancy risk
Testicular microlithiasis—multiple echogenic foci, associated with germ cell tumor risk in select populations
Congenital absence of the vas deferens (associated with CFTR mutations) and seminal vesicle agenesis/cysts
Persistent Müllerian remnants (prostatic utricle/Müllerian duct cyst) in the midline
Polyorchidism and epididymal/tunica albuginea cysts
Variant prostatic median lobe hypertrophy projecting into the bladder

Pathology Correlation

Prostate cancer: focal restricted diffusion and low T2 in the peripheral zone; extracapsular extension, seminal-vesicle invasion, and neurovascular bundle involvement determine staging
BPH: transition-zone nodular enlargement; encapsulated nodules can mimic or obscure cancer on MRI
Testicular torsion: enlarged, heterogeneous testis with absent intratesticular Doppler flow—a surgical emergency
Epididymo-orchitis: hyperemia with an enlarged, hypoechoic epididymis and reactive hydrocele
Testicular tumors: intratesticular solid masses (seminoma homogeneous; non-seminomatous heterogeneous)—any solid intratesticular lesion is malignant until proven otherwise
Varicocele: dilated pampiniform veins (>2-3 mm) with reflux on Valsalva, more common on the left and a cause of infertility

Pitfalls & Mimics

Central-zone and BPH nodules can mimic transition-zone cancer—apply PI-RADS T2 criteria carefully
Post-biopsy hemorrhage causes T1 hyperintensity that confounds MRI—image before biopsy or allow an interval
An extratesticular mass is usually benign, whereas an intratesticular solid lesion is malignant until proven otherwise—precisely localize
Intermittent or early torsion may retain some flow; a heterogeneous testis with clinical suspicion warrants surgery regardless
Do not mistake a hydrocele, spermatocele, or epididymal cyst for a solid mass
Anterior fibromuscular stroma and periprostatic structures can be mistaken for tumor on T2

References

ACR PI-RADS v2.1 Prostate Imaging Reporting and Data System
Dogra VS, et al. Sonography of the scrotum. Radiology / scrotal ultrasound literature
Hricak H, Scardino PT. Prostate Cancer (Contemporary Issues in Cancer Imaging). Cambridge
Rumack CM, Levine D. Diagnostic Ultrasound. Elsevier

⚕️ Educational reference — correlate with clinical context and confirm with a qualified radiologist.

Male Reproductive Anatomy

🧩 Key Structures

🎞️ Imaging Planes & Modalities

📏 Landmarks & Normal Values

🔀 Anatomical Variants

🧠 Pathology Correlation

💡 Pitfalls & Mimics