# Penile, Scrotal, and Inguinal Anatomy ## Overview Understanding the layered anatomy of the penis, the contents of the spermatic cord, the blood supply to the testicles, and the anatomy of the inguinal canal is essential for surgical procedures such as hydrocelectomy, varicocelectomy, and orchiectomy. Each of these anatomical regions has distinct structures and relationships that influence both function and surgical approach. --- ## Penile Anatomy ### Layered Structure (Superficial to Deep) The penis is composed of several layers arranged from superficial to deep. The outermost layer is the skin, which is thin, loosely attached, and highly elastic, notably lacking subcutaneous fat on the penile shaft. Beneath the skin lies the dartos fascia, also known as the superficial fascia, which is a continuation of Scarpa's fascia from the abdomen and the dartos layer of the scrotum; this layer contains smooth muscle fibers. Deeper still is Buck's fascia, the dense and strong investing fascia that individually encloses all three erectile bodies of the penis. Buck's fascia plays an important role in limiting the spread of hematomas; for example, when a penile fracture hematoma is confined within Buck's fascia, it produces the characteristic "eggplant deformity." The tunica albuginea is a thick fibrous coat surrounding each corpus cavernosum, approximately 2 mm thick, and the corpus spongiosum, which has a thinner tunica albuginea of about 0.5 mm. This fibrous layer provides rigidity during erection. Finally, the erectile tissue itself consists of the paired corpora cavernosa and the single ventral corpus spongiosum. ### Erectile Bodies The paired corpora cavernosa arise from the ischiopubic rami as the crura and unite beneath the pubic symphysis. They are separated by an incomplete midline septum called the pectiniform septum, which allows pressure equalization between the two bodies during erection. Each corpus cavernosum is surrounded by a thick tunica albuginea composed of outer longitudinal and inner circular layers. The vascular spaces within these bodies are sinusoidal and lined by endothelium, facilitating blood filling during erection. The corpus spongiosum surrounds the urethra and expands distally to form the glans penis. Proximally, it expands to form the bulb, which is covered by the bulbospongiosus muscle. Its tunica albuginea is thinner than that of the corpora cavernosa, which prevents full rigidity and thus protects the urethra from compression during erection. ### Penile Blood Supply Arterial blood supply to the penis originates from the internal pudendal artery, which gives rise to the common penile artery. This artery branches into the cavernosal (deep) artery, dorsal artery, and bulbourethral artery. The cavernosal artery is the central artery within each corpus cavernosum and gives off helicine arteries; it is the primary artery responsible for erection. The dorsal artery runs beneath Buck's fascia on the dorsum of the penis, positioned dorsal to the deep dorsal vein and between the dorsal nerve laterally; it supplies the glans and penile skin. The bulbourethral artery supplies the bulb, corpus spongiosum, and urethra. Venous drainage includes the superficial dorsal vein, which lies superficial to Buck's fascia and drains into the saphenous vein, and the deep dorsal vein, located beneath Buck's fascia between the paired dorsal arteries, which drains into the periprostatic (Santorini) plexus. Emissary veins from the sinusoidal spaces pierce the tunica albuginea and are compressed during erection, contributing to the corporal veno-occlusive mechanism. The cavernosal veins drain blood from the crura. ### Penile Innervation Somatic sensory and motor innervation is provided by the dorsal nerve of the penis, a branch of the pudendal nerve arising from spinal segments S2 to S4. This nerve runs on the dorsum of the penis lateral to the dorsal artery and beneath Buck's fascia, supplying sensation to the penile skin and glans. Autonomic innervation consists of parasympathetic cavernous nerves from the pelvic plexus (S2-S4), which enter the corpora cavernosa at the hilum near the crura junction. These nerves mediate erection through the release of nitric oxide, which increases cyclic GMP and causes smooth muscle relaxation. Sympathetic fibers arise from the hypogastric plexus (T11-L2) and mediate detumescence and ejaculation. ### Dorsal Penile Neurovascular Bundle The dorsal neurovascular bundle is arranged from the midline outward as vein, artery, and nerve, remembered by the mnemonic "VAN." Specifically, the deep dorsal vein lies medially, followed by the paired dorsal arteries, and then the dorsal nerves laterally. All these structures lie beneath Buck's fascia and dorsal to the corpora cavernosa. ### Foreskin (Prepuce) The foreskin is a double layer of skin covering the glans penis. Its inner mucosal layer is continuous with the glans epithelium. On the ventral surface, the frenulum contains the frenular artery, which is a common source of bleeding during circumcision. --- ## Scrotal Anatomy ### Layers of the Scrotum (Superficial to Deep) The layers of the scrotum correspond closely to those of the anterior abdominal wall. From superficial to deep, these include the skin, dartos muscle and fascia (equivalent to Scarpa's fascia), external spermatic fascia (from the external oblique aponeurosis), cremasteric muscle and fascia (from the internal oblique muscle), internal spermatic fascia (from the transversalis fascia), and the tunica vaginalis, which has parietal and visceral layers derived from the processus vaginalis (peritoneum). The innermost layer is the tunica albuginea, which is specific to the testis. ### Scrotal Blood Supply The scrotum receives blood from several arteries. The anterior scrotal arteries arise from the external pudendal artery, a branch of the femoral artery. The posterior scrotal arteries come from the internal pudendal artery, itself a branch of the internal iliac artery. The cremasteric artery, originating from the inferior epigastric artery, also contributes. These vessels form a rich anastomotic network, which ensures that scrotal skin flaps are well vascularized, an important consideration in reconstructive surgery. ### Scrotal Innervation The anterior scrotum is innervated by the ilioinguinal nerve (L1) and the genital branch of the genitofemoral nerve (L1-L2). The posterior scrotum receives innervation from the posterior scrotal branches of the pudendal nerve (S2-S4) and the perineal branch of the posterior femoral cutaneous nerve. --- ## Testicular Anatomy ### Gross Anatomy The testis typically measures approximately 4.5 by 2.5 by 3 cm, with a volume ranging from 15 to 25 mL, as measured by a Prader orchidometer. It is surrounded by the tunica albuginea, a dense fibrous capsule that sends septa inward, dividing the testis into 250 to 300 lobules. Each lobule contains one to three seminiferous tubules, which converge into the tubuli recti, then the rete testis, followed by the efferent ductules, and finally the epididymis. ### Testicular Blood Supply The testicular (internal spermatic) artery arises directly from the aorta just below the renal arteries and is notable for being the longest artery in the body relative to the organ it supplies. It travels within the spermatic cord. Additional arterial supply comes from the artery of the vas deferens (deferential artery), which originates from the superior or inferior vesical artery, and the cremasteric artery, which arises from the inferior epigastric artery. These three arteries form a free anastomotic network, allowing for procedures such as Fowler-Stephens orchiopexy, where the testicular artery can be ligated if the deferential artery remains intact. ### Testicular Venous Drainage Venous drainage is primarily through the pampiniform plexus, a network of veins surrounding the testicular artery within the spermatic cord. This plexus coalesces into the testicular vein and functions as a countercurrent heat exchanger to cool arterial blood. Dilation of these veins leads to varicocele formation. The left testicular vein drains into the left renal vein at a right angle, whereas the right testicular vein drains directly into the inferior vena cava at an oblique angle. The right-angle insertion and longer venous column on the left side explain the higher incidence of left-sided varicoceles. ### Epididymis The epididymis is divided into three parts: the head (caput), which receives the efferent ductules and is the largest portion; the body (corpus), which lies along the posterolateral aspect of the testis; and the tail (cauda), which is continuous with the vas deferens and serves as a sperm storage site. The blood supply to the epididymis comes from the testicular artery at the head and the deferential artery at the tail. --- ## Spermatic Cord ### Contents The spermatic cord contains three arteries: the testicular artery, deferential artery, and cremasteric artery. It also contains three veins, including the pampiniform plexus (testicular veins), deferential vein, and cremasteric vein. Three nerves are associated with the cord: the ilioinguinal nerve, which lies outside the cord on the external spermatic fascia; the genital branch of the genitofemoral nerve, responsible for the cremasteric reflex; and sympathetic fibers that accompany the testicular artery. Other structures within the cord include the vas deferens, lymphatic vessels, and remnants of the processus vaginalis. The cord is covered by three layers: the internal spermatic fascia, cremasteric muscle and fascia, and external spermatic fascia. ### Vas Deferens The vas deferens is a thick-walled muscular tube approximately 3 mm in outer diameter with a tiny lumen. It is palpable within the spermatic cord as a cord-like structure. Its course begins at the epididymal tail, passes through the inguinal canal, crosses over the external iliac vessels, travels posterior to the bladder, and expands into the ampulla before joining the seminal vesicle duct to form the ejaculatory duct. --- ## Inguinal Canal ### Boundaries The inguinal canal is bounded anteriorly by the external oblique aponeurosis along its entire length, with the internal oblique muscle contributing to the lateral one-third. The posterior wall or floor consists of the transversalis fascia throughout and the conjoint tendon medially in the medial one-third. The roof is formed by arching fibers of the internal oblique and transversus abdominis muscles. The floor is defined by the inguinal (Poupart) ligament and the lacunar ligament medially. ### Rings The deep (internal) inguinal ring is an opening in the transversalis fascia located lateral to the inferior epigastric vessels. The superficial (external) ring is an opening in the external oblique aponeurosis, situated medial and superior to the pubic tubercle. ### Inguinal Canal Contents (Males) In males, the inguinal canal contains the spermatic cord and its contents as previously described. The ilioinguinal nerve runs on the cord but is not contained within it. ### Hesselbach Triangle (Inguinal Triangle) The Hesselbach triangle is bounded laterally by the inferior epigastric vessels, medially by the lateral border of the rectus abdominis muscle, and inferiorly by the inguinal ligament. Direct inguinal hernias protrude through this triangle medial to the inferior epigastric vessels, whereas indirect inguinal hernias pass through the deep ring lateral to these vessels. --- ## Surgical Applications ### Radical Inguinal Orchiectomy This procedure involves an inguinal incision approximately 2 cm above the inguinal ligament. The external oblique aponeurosis is opened along its fibers to expose the spermatic cord, which is identified and controlled at the deep ring before delivering the testis. The testis is removed en bloc with the cord structures. The spermatic cord is clamped and ligated separately at the level of the deep ring. A scrotal approach is avoided to prevent alteration of lymphatic drainage pathways, which could affect oncologic outcomes. ### Hydrocelectomy Hydrocelectomy can be performed via a scrotal or inguinal approach. The scrotal approach includes the Lord plication technique, which involves plicating the tunica vaginalis without excision, and the Jaboulay eversion technique, where the tunica vaginalis is opened, the sac everted, and sutured behind the cord structures. ### Microsurgical Varicocelectomy This procedure can be performed via a subinguinal approach, which is below the external ring and does not require fascial incision, or an inguinal approach, which involves opening the external oblique and delivering the cord. Under an operating microscope, the internal spermatic veins and external spermatic or cremasteric veins are ligated while preserving the testicular artery, lymphatics, and vas deferens. The artery is identified by its pulsation and can be confirmed with micro-Doppler. ### Vasectomy Vasectomy is typically performed through a scrotal approach using either a small incision or a no-scalpel technique. The vas deferens is identified by palpation as a hard, cord-like structure. A segment is excised, and the ends are cauterized with fascial interposition to prevent recanalization. --- A detailed cross-sectional diagram of the penis at the mid-shaft level showing all layers from skin to erectile tissue: skin, dartos fascia, Buck fascia, tunica albuginea, paired corpora cavernosa with the septum between them, and the ventral corpus spongiosum surrounding the urethra. The deep dorsal vein, paired dorsal arteries, and paired dorsal nerves are shown in their anatomic positions on the dorsum beneath Buck fascia. The cavernosal arteries are shown centrally within each corpus cavernosum. All structures are clearly labeled with color coding. An anterior view of the inguinal canal with the external oblique aponeurosis partially reflected to show the spermatic cord passing through the deep (internal) ring at the level of the transversalis fascia and exiting through the superficial (external) ring. The contents of the spermatic cord are displayed in an exploded view: testicular artery, deferential artery, cremasteric artery, pampiniform plexus, vas deferens, and the three fascial coverings. Hesselbach triangle is outlined with its boundaries labeled (inferior epigastric vessels, rectus border, inguinal ligament). A sagittal view of the scrotum and testis showing all layers from skin to the tunica albuginea, with each layer labeled and color-matched to its corresponding anterior abdominal wall layer. The tunica vaginalis (parietal and visceral layers) is clearly shown with the potential space between them (where hydrocele fluid accumulates). The epididymis is shown along the posterolateral testis with its three parts (head, body, tail) labeled and continuing into the vas deferens. --- ## Clinical Pearls Buck's fascia plays a critical role in confining hematomas resulting from penile fractures to the penile shaft, producing the characteristic "eggplant deformity." If Buck's fascia is disrupted, blood can track into the scrotum and perineum along the dartos and Colles fascia, creating a "butterfly" pattern of bruising. The left testicular vein drains into the left renal vein at a right angle, whereas the right testicular vein drains obliquely into the inferior vena cava. This anatomical difference explains the higher incidence of left-sided varicoceles. The appearance of a new right-sided or non-decompressing varicocele in an older male should raise suspicion for retroperitoneal pathology, such as renal cell carcinoma with renal vein thrombus. During microsurgical varicocelectomy, preserving the testicular artery is essential; it can be identified by its pulsation or with the aid of micro-Doppler. Typically, one to two arteries are present at the subinguinal level. The three testicular arterial sources—the testicular, deferential, and cremasteric arteries—anastomose freely, which forms the basis for the Fowler-Stephens orchiopexy procedure where the testicular artery is intentionally ligated. In radical inguinal orchiectomy, early control of the spermatic cord at the deep ring before manipulating the testis helps prevent tumor dissemination. The ilioinguinal nerve runs superficially over the spermatic cord structures and is at risk during inguinal incisions; injury to this nerve causes numbness or pain in the inguinal region and anterior scrotum. --- ## References - Campbell-Walsh-Wein Urology, 12th Edition — Chapter 1: Anatomy of the Lower Urinary Tract and Male Genitalia - Hinman's Atlas of Urologic Surgery, 4th Edition - Goldstein M. Microsurgical varicocelectomy. In: Goldstein M, ed. Surgery of Male Infertility. 1995 - Netter FH. Atlas of Human Anatomy, 7th Edition — Plates of the Perineum and External Genitalia