Summary of "Introduction to CT Abdomen and Pelvis: Anatomy and Approach"

This educational video provides a comprehensive introduction to interpreting CT scans of the abdomen and pelvis, focusing primarily on normal anatomy, key anatomical landmarks, and a systematic approach to reading these scans. It is the first part of a two-part series, with this video emphasizing anatomy and the basic approach, while the subsequent video will cover common pathologies and clinical pearls.

Main Ideas and Concepts

Preliminary Recommendations:
- Viewers are encouraged to watch a prior video on CT basics covering Hounsfield units, tissue densities, windowing, IV contrast, and contrast phases before this anatomy-focused lecture.
Peritoneal Anatomy:
- The abdominal cavity is divided into the peritoneal cavity (lined by the Peritoneum) and the retroperitoneum (behind the Peritoneum).
- The Peritoneum is a continuous, thin epithelial membrane with two parts:
  - Parietal Peritoneum: lines the abdominal wall.
  - Visceral Peritoneum: envelops abdominal organs.
- The space between these layers is the peritoneal cavity, where free fluid or gas can accumulate.
- Peritoneal ligaments (double layers of Peritoneum) include:
  - Omenta: ligaments originating from the stomach (greater and lesser omentum).
  - Mesentery: ligaments connecting organs to the posterior abdominal wall (e.g., small bowel mesentery, transverse mesocolon).
- These ligaments contain fat, blood vessels, and lymph nodes visible on CT.
- Clinical relevance: Peritoneal ligaments act as pathways for disease spread (e.g., peritoneal metastases causing omental caking, often from ovarian or GI cancers).
Peritoneal Spaces:
- Important spaces where fluid or pathology may accumulate:
  - Right and left subphrenic spaces (under diaphragm).
  - Morrison’s pouch (hepatorenal recess): collects fluid in trauma.
  - Paracolic gutters (right and left): pathways for fluid or metastases.
  - Pelvic spaces:
    - Females: rectouterine pouch (pouch of Douglas), uterovesical space.
    - Males: rectovesical space.
- Knowledge of these spaces aids in identifying fluid collections or metastatic disease.
Retroperitoneal Anatomy:
- The retroperitoneum contains:
  - Perirenal space: contains kidneys and adrenal glands, bounded by anterior (Gerota’s fascia) and posterior (Zuckerkandl’s fascia) perirenal fascia.
  - Anterior pararenal space: contains pancreas, ascending and descending colon, parts of the duodenum.
  - Posterior pararenal space: mostly fat.
- Clinical importance in conditions like pancreatitis where inflammation tracks along these spaces.
- Other extraperitoneal spaces include:
  - Prevesical space (space of Retzius).
  - Perivesical spaces.
  - Presacral space.
Bladder Rupture Types:
- Differentiation between extraperitoneal and intraperitoneal bladder ruptures is critical as management differs:
  - Intraperitoneal ruptures usually require surgery.
  - Extraperitoneal ruptures often managed conservatively.
Abdominal Organ Anatomy:
- Liver:
  - Divided into 8 segments based on hepatic and portal veins.
  - Hepatic veins (right, middle, left) divide liver into four vertical sections.
  - Portal vein divides liver into superior and inferior halves.
  - Knowledge of segmental anatomy is vital for surgical planning and reporting.
  - Common sites of focal fat include adjacent to falciform ligament and Gallbladder fossa.
- Gallbladder and Biliary Tree:
  - Gallbladder has fundus, body, and neck; stones often lodge in neck causing cholecystitis.
  - Cystic duct joins common hepatic duct to form common bile duct (CBD).
  - Normal CBD diameter <6 mm at age 60, increasing 1 mm per decade thereafter.
  - Biliary dilatation and stones (Choledocholithiasis) can be identified on CT.
  - Common biliary variants include trifurcation and early branching of right posterior bile duct.
- Spleen:
  - Size varies; accessory spleens (splenules) are common.
  - Normal max length ~13 cm.
- Pancreas:
  - Divided into head, neck, body, and tail.
  - Dorsal and ventral pancreas refer to embryologic origins but are reversed in position.
  - Pancreatic duct