Lec 28: Notę

Posterior Abdominal Wall

  • Composed of: Lumbar vertebrae (T12T12–L5L5), Diaphragm (superior), Muscles (psoas, quadratus lumborum, iliacus), and lower ribs (11th11th & 12th12th).

  • Fascial organization:

    • Thoracolumbar fascia: CT sheet covering posterior/lateral trunk muscles.

    • Endoabdominal (transversalis) fascia: Deep layer lining abdominal wall, named by muscle it overlies (e.g., psoas fascia).

Muscles of the Posterior Wall

  • Psoas Major:

    • Origin: Transverse processes, bodies, and IV discs of T12T12–L5L5.

    • Course: Descends, joins iliacus to form iliopsoas, inserts on lesser trochanter of femur.

    • Action: Primary hip flexor; also trunk flexor when leg is fixed.

    • Clinical Correlation: Weakness of core muscles, including those related to the thoracolumbar fascia, can lead to lumbar instability, often seen in low-back pain.

  • Quadratus Lumborum:

    • Origin: 12th12th rib and tips of lumbar transverse processes.

    • Insertion: Iliolumbar ligament and posterior iliac crest.

    • Actions: Ipsilateral trunk flexion, stabilizes rib 1212 during breathing, trunk stabilization.

Nerves of the Posterior Abdominal Wall (Lumbar Plexus & T12)

  • Formed by ventral rami L1L1–L4L4 (plus T12T12 contribution).

  • Subcostal nerve (T12T12):

    • Motor: Transversus abdominis (TA), Internal Oblique (IO).

    • Cutaneous: Anterolateral abdominal wall.

  • Iliohypogastric nerve (L1L1):

    • Motor: TA, IO.

    • Cutaneous: Hypogastric (suprapubic) skin.

  • Ilioinguinal nerve (L1L1):

    • Course: Passes along iliac crest, through inguinal canal.

    • Motor: TA, IO, External Oblique (EO).

    • Cutaneous: Anterior scrotum/labia majora, adjacent thigh.

  • Lateral Femoral Cutaneous nerve (L2L2–L3L3):

    • Course: Crosses iliacus, passes under inguinal ligament.

    • Cutaneous: Lateral thigh.

    • Clinical Correlation: Compression under the inguinal ligament can cause meralgia paresthetica (burning pain in the lateral thigh).

  • Femoral nerve (L2L2–L4L4):

    • Course: Between psoas and iliacus, enters thigh lateral to femoral sheath.

    • Motor: Iliopsoas, quadriceps femoris, sartorius, part of pectineus.

    • Cutaneous: Anterior thigh, medial leg.

  • Genitofemoral nerve (L1L1–L2L2):

    • Course: Pierces psoas major, splits into genital and femoral branches.

    • Motor (genital branch): Cremaster muscle.

    • Cutaneous: Scrotal/labial skin (genital branch), superior anterior thigh (femoral branch).

  • Obturator nerve (L2L2–L4L4):

    • Course: Descends medial to psoas, exits via obturator canal.

    • Motor: Medial thigh adductors.

    • Cutaneous: Medial thigh patch.

Diaphragm

  • Dome-shaped muscle separating thorax and abdomen.

  • Key Hiatuses:

    • T8T8 Caval foramen: Inferior Vena Cava (IVC), right phrenic nerve branch.

    • T10T10 Esophageal hiatus: Esophagus, vagal trunks. Formed by right crus fibers.

    • T12T12 Aortic hiatus: Descending aorta, thoracic duct, sometimes azygos/hemiazygos veins.

    • Clinical Correlation: Dysfunction of the right crus fibers at the esophageal hiatus can predispose to hiatal hernia and GERD (Gastroesophageal Reflux Disease).

    • Clinical Correlation: Median Arcuate Ligament Syndrome involves compression of the celiac trunk by the median arcuate ligament, causing post-meal pain usually relieved by leaning forward.

  • Physiology: Contraction pulls central tendon down, increasing thoracic volume for inspiration.

  • Innervation: Phrenic nerves (C3C3–C5C5).

Kidneys & Suprarenal (Adrenal) Glands

  • Kidneys: Retroperitoneal organs (T12T12–L3L3), filter blood, balance electrolytes/fluids.

  • Protective Layers (from posterior to anterior):

    1. Transversalis fascia.

    2. Pararenal (paranephric) fat: Thin posterior cushion.

    3. Renal (Gerota’s) fascia: Fibrous sheath surrounding the kidney and perirenal fat.

    4. Perirenal (perinephric) fat: Thick fat layer immediately outside the renal capsule.

    5. Renal capsule: Tough fibrous coat on kidney surface.

    • Clinical Correlation: Inadequate perirenal fat (e.g., from rapid weight loss) can lead to nephroptosis (kidney dropping) and kinking of the ureter.

    • Clinical Correlation: Severe obstruction in the collecting system, such as a kidney stone, can lead to increased intrapelvic pressure. This elevated pressure can, in rare cases, cause a ruptured renal calyx, leading to extravasation of urine into the perirenal space, causing sudden relief of colic but potentially leading to urinoma formation and infection. A ruptured abdominal aortic aneurysm (AAA) is a life-threatening medical emergency where a weakened, bulging section of the aorta (the body's largest artery, which runs through the abdomen) bursts. This condition typically causes severe, sudden pain in the abdomen or back, often described as tearing. Other symptoms can include lightheadedness, dizziness, rapid heart rate, and loss of consciousness due to massive internal bleeding. Aneurysms are often asymptomatic until they rupture, making early diagnosis challenging. Risk factors include advanced age, male gender, smoking, high blood pressure, high cholesterol, and a family history of aneurysms. Immediate surgical intervention is critical for survival.

    • Macro-anatomy:

    • Hilum: Medial indentation for renal vein, artery, and pelvis/ureter.

    • Internal: Cortex (outer, granular) and Medulla (8-18 pyramids).

    • Collecting system: Papilla → minor calyces → major calyces → renal pelvis → ureter.

    • Ureters: Muscular tubes carrying urine; renal colic (severe pain) occurs due to obstruction.

    • Clinical Correlation: Renal colic pain typically follows dermatomes T11T11–L2L2 due to shared nerve supply with the ureter.

  • Suprarenal Glands: Sit on kidneys; Cortex produces corticosteroids/androgens; Medulla produces catecholamines (epinephrine, norepinephrine).

Blood Supply & Venous Drainage

  • Kidneys:

    • Arteries: Paired renal arteries from the abdominal aorta at L1/L2L1/L2.

    • Veins: Renal veins drain into the IVC. The left renal vein is longer, passing anterior to the aorta and posterior to the Superior Mesenteric Artery (SMA), and receives the left gonadal and inferior phrenic veins.

  • Suprarenal Glands:

    • Arteries: Superior (from inferior phrenic a.), Middle (direct from aorta), Inferior (from renal a.).

    • Veins: Drain via suprarenal veins.