Internal Hernias in the Era of Multidetector CT: Correlation of Imaging and Surgical Findings
Executive Summary
Internal hernias represent a critical surgical emergency, accounting for approximately 4% of all cases of acute small bowel obstruction. They are defined as the protrusion of abdominal viscera through an opening within the peritoneal cavity. These openings may be congenital (normal foramina or peritoneal recesses) or acquired (secondary to trauma, inflammation, or surgery).
Clinical diagnosis is notoriously difficult due to nonspecific symptoms, such as nausea, vomiting, and abdominal pain, which can range from intermittent to acute. However, the advent of Multidetector Computed Tomography (MDCT) has revolutionized preoperative diagnosis. Through thin-section axial imaging, multiplanar reformations (MPRs), and three-dimensional (3D) reconstructions, MDCT allows for the precise identification of pathognomonic findings, including closed-loop obstructions and the displacement of landmark vessels. Early and accurate diagnosis is essential to prevent intestinal strangulation, ischemia, and necrosis.
Overview of Internal Hernias
Internal hernias occur when abdominal viscera, most commonly small bowel loops, herniate through an intraperitoneal orifice. These hernias are categorized based on the nature of the orifice:
Normal Foramen: e.g., Foramen of Winslow.
Unusual Peritoneal Fossa or Recess: Retroperitoneal recesses resulting from failures in peritoneal fusion.
Abnormal Openings: Defects in a mesentery or peritoneal ligament.
Degrees of Mesenteric Defects
When involving mesenteries or ligaments consisting of two peritoneal layers, hernias are further subcategorized:
Transmesenteric (Fenestra Type): The defect involves both peritoneal layers.
Intramesenteric (Pouch Type): The defect involves only one peritoneal layer, creating a sac.
The MDCT Diagnostic Framework
MDCT is currently the first-line imaging technique for internal hernias. The diagnostic approach follows a systematic three-step process:
Step 1: Detect an Intestinal Closed Loop
Internal hernias usually manifest as mechanical small bowel obstructions, specifically closed-loop obstructions where the segment is occluded at two adjacent points.
Key Finding: A U- or C-shaped, fluid-filled, distended intestinal loop.
Saclike Appearance: Crowding and sacculation of small bowel loops within a hernia sac. This is a strong indicator of internal hernia but is typically only seen in retroperitoneal or intramesenteric-type hernias.
Step 2: Identify the Hernia Orifice
The orifice is located where the bowel, mesenteric fat, and vessels of the closed loop converge.
MDCT Signs: Convergence, engorgement, and twisting of mesenteric vessels at the orifice point. Identification is mandatory for surgical planning to prevent recurrence.
Step 3: Analyze Displacement of Surrounding Structures and Key Vessels
Definitive diagnosis requires identifying the displacement of anatomic landmarks. Because mesenteries and ligaments are often invisible on CT unless outlined by ascites, radiologists must trace "landmark vessels" to approximate their locations.
Table 1: Landmark Vessels for Anatomic Identification
Detailed Examination of Specific Hernia Types
Paraduodenal Hernias
The most common congenital internal hernias, resulting from failures in peritoneal fusion.
Left Paraduodenal (Fossa of Landzert): The most frequent type. The IMV and ascending left colic artery serve as landmarks at the anteromedial border of the hernia sac.
Right Paraduodenal (Fossa of Waldeyer): Usually involves a nonrotated small intestine. The SMA and SMV run along the anteromedial free edge of the orifice.
Transmesenteric and Transomental Hernias
Transmesenteric: Currently the most prevalent type (excluding Roux-en-Y). These lack a saclike appearance and are frequently complicated by volvulus.
Transomental: Typically presents as a closed-loop intestine in the most anterior portion of the peritoneal cavity. Landmark vessels are the omental branches of the gastro-omental vessels.
Lesser Sac Hernias
The lesser sac is accessible only through the foramen of Winslow or through defects in the surrounding ligaments (lesser omentum, greater omentum, or transverse mesocolon).
Foramen of Winslow Hernia: The most common lesser sac type. Viscera (bowel, cecum, or gallbladder) enter through the epiploic foramen, often appearing as a "beak" shape pointing toward the foramen.
Other Types: Hernias through the gastrohepatic ligament are characterized by orifices located above the gastric vessels.
Pelvic and Pericecal Hernias
Pericecal Hernia: Involves recesses near the cecum; the hernia sac typically displaces the cecum and ascending colon medially or anteriorly.
Broad Ligament Hernia: Primarily seen in multiparous women. MPR images can depict mesenteric vessels penetrating the broad ligament.
Internal Supravesical Hernia: The intestine herniates into the retropubic space of Retzius, compressing the anterior wall of the urinary bladder.
Roux-en-Y Anastomosis-Related Hernias
Increasingly common following laparoscopic gastric bypass surgery. There are three primary subtypes:
Transmesocolic: Through the surgical defect in the transverse mesocolon.
Jejunojejunostomy Mesenteric: Through the defect in the small bowel mesentery.
Petersen Hernia: Occurs in the space between the Roux limb mesentery and the transverse mesocolon.
Surgical Management and Technical Considerations
MDCT Technique
Contrast: Intravenous contrast is essential for evaluating blood flow and identifying strangulation.
Oral Contrast: Generally considered unnecessary and may obscure bowel wall enhancement in high-grade obstructions.
Scanning: Multi-phasic scanning (arterial, portal venous, and delayed) is recommended. Nonenhanced scans are useful for detecting hemorrhagic congestion (hyperattenuating bowel wall).
Surgical Intervention
The primary goal is reduction of the herniated contents followed by a careful inspection for ischemia. Nonviable structures must be resected. To prevent recurrence, the hernia orifice is typically closed with sutures. While open laparotomy was the traditional standard, laparoscopic surgery is increasingly utilized due to shorter hospital stays and fewer complications. An internal hernia is a surgical emergency; accurate preoperative diagnosis via MDCT is the critical factor for appropriate management.
