General Comments

• Separates the abdomen from the thorax
• Convex toward the thorax
• 10 cm movement with maximum inspiration
• right dome at 6th costochondral joint level on expiration
• Left dome one rib lower than right
• central tendon is thin aponeurosis of trifoliate shape
• cura origin blends with the anterior longitudinal ligament

Parts of the diaphragm

• central tendon - central aspect of diaphragm
• tendinous site of attachment for coronary ligament (and pericardial sac)
• sternal portion - xiphoid process upward and backward to central tendon
• costal portion - inner surface of costal cartilages 7, 8, 9 bony 10, 11, 12
• lumbar portion - from the arcuate ligaments and lumbar vertebrae by way of the cura
• domed peripheral muscular part
• right crus of diaphragm
  • contributes to esophageal hiatus
  • inferior insertion extends to L3 anterior vertebral body
• left crus of diaphragm
  • inferior insertion extends to L2
• median arcuate ligament
  • fibrous ligamentous arch connecting diaphragmatic cura
  • forms anterior boundary of aortic hiatus
• medial arcuate ligament
  • posterior attachment of diaphragm to fascia of psoas major
  • vertebral level L1/L2
• lateral arcuate ligament
  • posterior attachment of diaphragm to fascia of quadratus lumborum
  • attachment to anterior aspect of the transverse process of L1
  • attachment to the mid-12th rib
  • vertebral level L1/L2
• lumbocostal trigone (arch) (Bochdalek's triangle) (vertebrocostal trigone)
  • thinning of muscle usually on the left and immediately superior to the lateral arcuate ligament
  • site of herniation
  • surgically at risk during renal surgery

Apertures

• aperture for the IVC (inferior vena cava) at vertebral level T8 * transmits the IVC and branches of the right phrenic nerve
• aperture for the esophagus (esophageal hiatus) at vertebral level T10
  • encloses by insertion of right crus into central tendon
  • phrenoesophageal ligament (transversalis fascia) seals between cavities
  • transmits the esophagus, anterior and posterior vagal nerve trunks, esophageal branches of the left gastric vessels
• aperture for the aorta (aortal hiatus) at vertebral level T12
  • boundaries - anterior is median arcuate ligament, lateral left is left crus, lateral right is right crus, posterior is the vertebral body of T12 and the anterior longitudinal ligament
  • transmits aorta, thoracic duct, lymph ducts, azygos vein, hemiazygos vein, ascending lumbar vein

Pathways of structures coursing between thorax and abdomen

• IVC enters abdomen through hiatus for IVC
  • branch of phrenic n.
• esophagus enters abdomen through esophageal hiatus at T10
  • anterior and posterior vagal nerves
  • esophageal a. v. from left gastric a. v.
• aorta enters abdomen through aortic hiatus at T12
  • thoracic duct
  • ascending lumbar veins or azygos v.
• piercing the cura of diaphragm
  • greater, lesser, least splanchnic nn
• medial to the medial arcuate ligament
  • sympathetic trunk and psoas major
• posterior to the lateral arcuate ligament
  • subcostal nerve and quadratus lumborum
• anterior diaphragm is pierced by superior epigastric vessels

Relations (limited to abdomen) - consider that the diaphragm is domed shaped

• Anterior aspect of diaphragm - right side
  • posterior lies the liver, gall bladder, and duodenal cap
• anterior diaphragm - left side
  • posterior - greater sac, lesser omentum, stomach, greater omentum, transverse colon
• superior diaphragm - right side
  • inferior - liver, IVC
• superior diaphragm - left side
  • inferior - aorta, stomach, and spleen
• posterior diaphragm - right side
  • anterior - left kidney and suprarenal g. and the liver
  • lateral - greater, lesser, least splanchnic nerves, celiac and superior mesenteric ganglia lie of the cura
• posterior diaphragm - left side
  • anterior - pancreas, duodenum, stomach, transverse colon, spleen, kidney and suprarenal g., lesser sac
• much of the inferior diaphragm is covered with peritoneum
  • the resulting peritoneal spaces between diaphragm and liver, stomach, and spleen are the subphrenic recess
• ligaments
  • coronary ligament
  • leinorenal ligament
  • suspensory ligament of the duodenum
  • phrenicocolic ligament

Vasculature and Lymphatic Drainage

• anterior peripheral by musculocutaneous a. v. and anterior intercostal a. v.
• posterior peripheral by posterior intercostal a. v.
• pericardiacophrenic vessels
• superior phrenic a. v.
• inferior phrenic a. v. - central tendon
  • right vein drains into IVC whereas the left drains into the left renal vein
• parasternal nodes
• posterior mediastinal nodes
• lumbar nodes

Innervation

• motor supply entirely by phrenic nerve
• peripheral sensory by intercostal n.
• central tendon motor and sensory by phrenic n.

General Anatomy of the Rectum

• rectosigmodal junction at S3 extending to tip of coccyx and ending at anorectal junction (pelvic floor)
• ends 2cm anterior and slightly inferior to the tip of the coccyx
• passes through pelvic diaphragm before anorectal junction
• 12 cm long with two convexities to right and one to left
• transverse folds - two on the right and one on the left (this is variable)
• teneia coli broaden to form longitudinal muscle layer
• no haustra or appendices epiploica
• smooth mucosa
• distensible at the rectal ampulla

Peritoneal coverings and relations

• upper 1/3 covered anterior and lateral
• middle 1/3 covered anterior
• lower 1/3 not peritonealized
• peritoneal pouches and fossa
• ant: rectouterine or rectovesical pouch
• lateral: pararectal fossae

Relations to surrounding structures

• Anterior - bladder, vagina, uterus, prostate, seminal vesical, vasdeferens, ureters
• Posterior - presacral space, sacrum, sacral foramina, sacral plexus, sacral sympathetic trunk, piriformis, middle and lateral sacral arteries
• lateral (left and right) - inferior hypogastric plexus, pelvic wall and associated structures, appendix on right
• Superior - sigmoid colon, false pelvis
• Inferior - anal canal, pelvic floor

Ligaments and support

• Rectovesical - part of the pubosacral ligamentous complex (derived from pelvic visceral fascia)
• Rectosacral - part of the pubosacral ligamentous complex (derived from pelvic visceral fascia)

Innervation (no somatic for rectum proper)

• sympathetic - inhibitory to muscles of the rectal wall
  • Preganglionic: IMLL L1-3 - white rami - lumbar sympathetic trunk - lumbar splanchnics - aortic plexus - inferior mesenteric ganglion
  • Postganglionic: inferior mesenteric plexus - superior rectal aa, right and left hypogastric nerves to rectal plexus
• parasympathetic - relax internal anal sphincter, glandular secretion
  • Preganglionic: pelvic splanchnic nerves leave ventral rami of S2-4 spinal nerves to enter the pelvic plexus on either side of the rectum (inferior hypogastric plexus)
  • an extension of the pelvic plexus either independently or via the left hypogastric nerve contributes to rectal plexus
  • postganglionic: cell bodies and fibers are located in enteric (intrinsic) ganglia
• Visceral afferent fibers
  • low threshold (homeostatic) follow parasympathetic pathways
  • high threshold (pain) follow sympathetic pathways

Vasculature Supply

• superior rectal aa pair on lateral posterior rectum - derived from single continuation of inferior mesenteric a - provides superior aspect of rectum
• superior rectal vein - drains most of the entire venus plexus of the rectum
• middle rectal artery - from internal iliac - provides inferior aspect of rectum
• inferior rectal artery - from pudendal artery - anastomosis with middle rectal artery
• median sacral artery at the posterior aspect of the anorectal junction
• rectal venous plexus drains to prostatic plexus or uterovaginal plexus
• inferior rectal and superior rectal veins form an interface between caval and portal drainages
• epirectal lymph nodes drain superior toward upper lumbar nodes near the inferior mesenteric nodes
• pararectal nodes drain laterally into internal iliac nodes

General Anatomy of the Anal Canal

• begins at anorectal junction and ends at anal verge
• 2.5 - 5 cm long
• anterior flexion by puborectal sling (puborectalis)
• transisition from cuboidal to squamous epithelium at the dentate line
• layers - inner epithelium, vascular subepithelium, internal anal sphincter, external anal sphincter, fibromuscular support tissue
• anterior attachment to perineal body
• posterior attachment to anococcygeal raphe
• surrounded by ischiorectal fat
• rectal circular muscle becomes internal anal sphincter
• puborectalis is continuous with external anal sphincter
• anal columns end at anal valves
• anal valves and sinuses mark the dentate line and the anorectal junction
• stratified squamous epithelium inferior to dentate line
• stratified columnar epithelium superior to dentate line
• anal tranisition zone (ATZ) not same as dentate line but may include it
• haemorrhoids of the anal cushions are superior to dendate line and may reflect portal hypertension

Innervation of the Anal Canal

• distal to dentate line
  • somatic motor and sensory by pudendal nerve
  • defined pain
• proximal to dentate line
  • visceromotor by autonomic nervous system (see above for rectum)
  • visceral afferent follow autonomic pathways (see above for rectum)
  • "dull ache"
• external anal sphincter by inferior rectal branches of the pudendal nerve
• internal anal sphincter by autonomic nerves

Vasculature of the Anal Canal

• proximal - superior rectal artery/vein and median sacral artery/vein
• distal - inferior rectal artery/vein from the internal pudendal artery/vein
• proximal lymphatic drainage - upper lumbar nodes
• distal lymphatic drainage - superficial inguinal nodes and internal iliac nodes

General Comments

• The spermatic cord is the pedicle of testis. Beginning at the deep ring, the spermatic cord transmits the contents of the deep ring from the abdominopelvic cavity to the scrotum.
• The pathway from the deep ring to the scrotum marks the "descent" of the testis.
• A peritonealized surface of the testis causes a trailing diverticulum know as the processes vaginalis.
• Applied to the anterior aspect of the testis is the visceral layer of tunica vaginalis.
• The deep ring marks the beginning of the inguinal canal and is located: at the midinguinal point; lateral to the inferior epigastric artery; and slightly more than 1 cm superior to the inguinal ligament.
• At the deep ring the spermatic cord receives the internal spermatic fascia derived from transversalis fascia. Within the inguinal canal the internal oblique contributes the cremasteric fascia.
• The cord exits the inguinal canal by way of the superficial ring.
• The superficial ring, a defect in the external oblique aponeurosis, contributes the external spermatic fascia.
• The testis, at the distal extent of the cord, ultimately resides within the scrotum. It is tethered to the most inferior aspect of the scrotum by the scrotal ligament.
• The external spermatic fascia (deep fascia) is opposed to dartos fascia (superficial fascia).

Internal Spermatic Fascia. Structures that pass through the deep ring were retroperitoneal and reside within the internal spermatic fascia derived from transversalis fascia.

• processes vaginalis - a trailing diverticulum of peritoneum that accompanies the testis during the "descent."
• Distally, within the scrotum, the processes vaginalis opens into the tunica vaginalis
• Extraperitonial connective tissue
• Testicular artery - paired branches from lumbar aorta near renal arteries
• Testicular vein - proximally the testicular vein consists of 3-4 veins
• Distally the testicular surrounds the testicular artery forming the pampinifrom plexus veins numbering 10 to 12 veins
• Left testicular vein drains into left renal vein and the right testicular vein drains into the IVC near the renal artery
• Testicular lymphatics - provide drainage to upper lumbar nodes, to lumbar lymph ducts, to cysterna chyli
• Testicular autonomic plexus - sympathetic preganglionic cell bodies in IMLCC T10(11-12)
  • Symmpathetic postganglionic cell bodies in superior mesenteric ganglion
  • Parasympathetic preganglionic fibers derived from the vagus nerve
• Afferent "pain" fibers following sympathetic pathways to spinal levels T10(11-12)
• Vas deferens - under sympathetic control, the walls (2-3 mm thick) of the vas deferens contract to discharge spermatozoa
• Within the cord the Vas deferens lies posterior to the testicular artery
• Distally, the Vas deferens forms the tail of the epididymis at the posterior inferior pole of testis
• Further distally the tail gives way to the body and then to the head of the epididymis at the posterior superior pole
• Deferential artery - branch of the internal iliac artery vascularizes the vas deferens and anastomoses with the testicular artery
• Deferential autonomic plexus - derived from the superior/inferior hypogastric autonomic plexus to prostatic plexus
  • Parasympathetic preganglionic fibers possibly derived from pelvic splanchnics (S2-4)
  • Afferent "pain" fibers following sympathetic pathways to spinal levels T10(11-12)
• Deferential lymphatics - drainage to internal iliac nodes, to lumbar lymph ducts, to cysterna chyli
• Genital branch of genitofemoral nerve - mediates efferent component of cremasteric reflex
• Cremesteric artery - branch of inferior epigastric artery vascularizes the tunics

The cremesteric fascia is superficial to the internal spermatic fascia and deep to the external spermatic fascia

• Derived from internal oblique muscle, the cremesteric fascia contributes to the cord within the inguinal canal
• Genital branch of the genitofemoral nerve - provides somatic motor supply
• Cremesteric artery - branches provide vascularization to the cremesteric fascia

The external spermatic fascia is superficial to the cremesteric fascia and is the outer most tunic

• Derived from the external oblique, the external spermatic fascia extends to the cord beyond the superficial ring
• Within the scrotum the external spermatic fascia is deep to dartos tunic

Path of indirect inguinal hernia

• An indirect hernia follows the embryologic "descent" of the testis indirectly out the superficial ring by way of the deep ring.
• A patent processes vaginalis allows herniated material to pass through the deep ring lateral to the inferior epigastric artery
• Herniated material passes through the inguinal canal and out the superficial ring - superior and medial to pubic tubercle
• Distally, the hernia is arrested by the tunica vaginalis
• In the case of herniated intestine, visceral peritoneum is directly opposed to visceral and parietal tunica vaginalis
• Palpation of the hernia occurs at the anterior aspect of the testis within the scrotum
• The long and curvaceous path of an indirect hernia make strangulation a distinct possibility