Perineum Anatomy

Perineum

• The perineum is the region inferior to the pelvic diaphragm, located between the thighs and buttocks

Borders

• The pubic symphysis is anterior
• The coccyx is posterior
• The ischiopubic rami and ischial tuberosities are lateral
• An imaginary line joining the ischial tuberosities divides the perineum into two triangles
• The urogenital triangle is anterior
• The anal triangle is posterior

Contents

Anal Triangle

• The anal triangle includes the anal canal and associated structures
• Ischial fat pads are located on either side of the anal canal

Urogenital Triangle

• The urogenital triangle includes the penis and scrotum in males
• The urogenital triangle includes the vulva in females
• The perineal membrane is a fibrous layer that provides attachment for the external genitalia

Perineal Body

• A fibromuscular mass at the center of the perineum, at the junction of the urogenital and anal triangles
• An attachment point for several muscles
• These muscles include the bulbospongiosus, external anal sphincter, and superficial transverse perineal muscles
• Important for pelvic floor support, particularly in females

Perineal Membrane

• A tough, triangular fascial structure that spans the urogenital triangle
• Provides a structure for attachment of the external genitalia

Muscles of the Perineum

Superficial Perineal Muscles

• Bulbospongiosus constricts the urethra and erects the penis in males
• Bulbospongiosus constricts the vagina in females
• Ischiocavernosus maintains erection of the penis or clitoris by compressing the crus
• Superficial transverse perineal supports the perineal body

Deep Perineal Muscles

• Deep transverse perineal supports the perineal body
• External urethral sphincter controls urination
• Compressor urethrae (females only) compresses the urethra
• Sphincter urethrovaginalis (females only) constricts both urethra and vagina

Other Muscles

• Levator ani supports the pelvic organs and controls defecation
• Coccygeus supports the pelvic organs

Nerves of the Perineum

• Pudendal nerve (S2-S4) provides sensory and motor innervation to the perineum and external genitalia
• Branches include the inferior rectal nerve, perineal nerve, and dorsal nerve of the penis or clitoris

Blood Supply of the Perineum

• Internal pudendal artery is the primary blood supply
• Branches include the inferior rectal artery, perineal artery, and dorsal artery of the penis or clitoris

Clinical Significance

• Episiotomy is a surgical incision of the perineum during childbirth to enlarge the vaginal opening
• Perineal tears can occur during childbirth, ranging in severity from first-degree to fourth-degree tears
• Pudendal nerve entrapment can cause chronic perineal pain

Peritoneal Cavity

• Potential space between the parietal and visceral peritoneum
• Contains serous fluid that lubricates the surfaces of the peritoneum, allowing organs to move freely
• Closed in males
• Continuous with the pelvic cavity through the uterine tubes, uterus, and vagina in females

Peritoneum

• A serous membrane lining the abdominal and pelvic cavities
• Composed of two layers
• The parietal peritoneum lines the abdominal wall
• The visceral peritoneum covers the organs
• The peritoneal cavity exists between these two layers

Divisions of the Peritoneal Cavity

• Greater sac is the main compartment
• Lesser sac (omental bursa) is a smaller compartment located posterior to the stomach and lesser omentum
• The greater and lesser sacs communicate through the omental foramen (foramen of Winslow)

Mesenteries

• Double layers of peritoneum that suspend the abdominal organs from the posterior abdominal wall
• Provide a pathway for blood vessels, nerves, and lymphatic vessels to reach the organs
• Examples include the mesentery of the small intestine, transverse mesocolon, and sigmoid mesocolon

Omenta

• Double layers of peritoneum that extend from the stomach to other abdominal organs
• The greater omentum extends from the greater curvature of the stomach and drapes over the small intestine
• The lesser omentum extends from the lesser curvature of the stomach to the liver

Peritoneal Ligaments

• Double layers of peritoneum that connect two organs or an organ to the abdominal wall
• The falciform ligament connects the liver to the anterior abdominal wall
• The hepatogastric ligament connects the liver to the stomach
• The hepatoduodenal ligament connects the liver to the duodenum
• The hepatoduodenal ligament contains the portal triad (portal vein, hepatic artery, and bile duct)
• The splenorenal ligament connects the spleen to the kidney
• The gastrosplenic ligament connects the stomach to the spleen

Peritoneal Reflections

• Areas where the peritoneum folds over itself to cover organs or form mesenteries and ligaments
• Examples include the greater and lesser omentum, mesentery of the small intestine, and various peritoneal ligaments

Intraperitoneal Organs

• Almost completely surrounded by peritoneum
• Mobile and have a mesentery
• Examples include the stomach, small intestine, liver, spleen, and uterus

Retroperitoneal Organs

• Lie behind the peritoneum and are only partially covered by it
• Less mobile and do not have a mesentery
• Primary retroperitoneal organs: kidneys, adrenal glands, ureters, aorta, inferior vena cava
• Secondarily retroperitoneal organs: pancreas, duodenum (parts 2-4), ascending colon, and descending colon

Clinical Significance

• Peritonitis is inflammation of the peritoneum, often caused by infection or chemical irritation
• Ascites is accumulation of fluid in the peritoneal cavity
• Paracentesis is surgical puncture of the abdominal wall to remove fluid from the peritoneal cavity
• Adhesions are abnormal connections between organs or between organs and the abdominal wall, often caused by surgery or inflammation