Meckels Diverticulum

A. Development and Anatomy of Meckel's Diverticulum

I. Epidemiology

• Most common congenital anomaly of the gastrointestinal (GI) tract.
• Prevalence: Approximately 0.2% to 4% of the population has a Meckel's diverticulum. 2% figure is commonly cited but not exact.
• Rule of 2's: While helpful, the "Rule of 2's" is an oversimplification and not always strictly accurate, but it is commonly used to recall the general features of Meckel's diverticulum:

• 2% of the population has a Meckel's diverticulum (Range is actually 0.2-4%, so not exactly 2%).
• Within 2 feet of the ileocecal valve on the antimesenteric border (typically). (This can be a wider range; generally within 100 cm).
• 2 inches in length (average size). (The average is closer to 3 cm, or just over 1 inch).
• Presents before age 2 (50% of cases). Symptomatic presentation is common in younger children, but can occur at any age.
• Twice as common in males compared to females (symptomatic Meckel's diverticulum is more common in males; 2:1 ratio).

II. Embryological Origin

• Vitelline Duct (Omphalomesenteric Duct): The key structure in the development of Meckel's diverticulum is the vitelline duct (also known as the omphalomesenteric duct). This duct connects the embryonic yolk sac to the primitive midgut during early fetal development. It's crucial for providing nutrients to the developing embryo before the placenta is fully functional.
• Obliteration Process: Normally, the vitelline duct undergoes complete obliteration (closure) during the 5th to 8th week of gestation. As the placenta matures and becomes the primary source of fetal nutrition, the vitelline duct is no longer needed and naturally regresses. The viscera also returns to an intraabdominal position during the 5th-7th week of life.
• Failure of Vitelline Duct Obliteration: A Meckel's diverticulum develops when this obliteration process is incomplete, between the fifth and seventh week of gestation. It represents a persistent remnant of the vitelline duct.
• Most common remnant of the omphalomesenteric duct (90%). Other, less common, remnants include:

• Umbilical fistula (patent vitelline duct).
• Umbilical sinus (partial patency at the umbilicus).
• Umbilical cyst (a cyst along the course of the vitelline duct).
• A fibrous cord connecting the ileum to the umbilicus.

III. Pathology and Anatomy of Meckel's Diverticulum:

• Definition: A true diverticulum. This means it contains all three layers of the bowel wall:

• Mucosa (innermost lining)
• Submucosa
• Muscularis propria (muscle layer)
• Serosa (outermost layer)
• This is an important point in differentiating it from a pseudo diverticulum, which only has the mucosa/submucosa

• Location: Located on the antimesenteric border of the distal ileum, typically within 100 cm (40 inches) of the ileocecal valve. Give or take this 100cm rule because a Meckels can be up to 2 meters!
• Size: Variable in size. The average length is around 3 cm, but can range from 1 cm to as large as 26 cm.
• Blood Supply: The blood supply to a Meckel's diverticulum is derived from the superior mesenteric artery (SMA). During embryonic development, the vitelline ducts are supplied by paired vitelline arteries. The left vitelline artery typically involutes, while the right vitelline artery persists and becomes the SMA. Therefore, the Meckel's diverticulum's blood supply branches directly from the SMA via the midgut mesentery.
• Histology (Ectopic Tissue): A significant characteristic of Meckel's diverticulum is the potential presence of ectopic tissue (tissue not normally found in that location). Found in up to 50% of diverticuli.

• Lined by ileal mucosa. Ectopic gastric mucosa can be a source of complications including bleeding, ulceration, and perforation.
• Common Ectopic Tissue:

• Gastric mucosa (most common)
• Pancreatic tissue

• Less Common Ectopic Tissue:

• Colonic mucosa
• Duodenal mucosa
• Jejunal mucosa
• Hepatobiliary tissue
• Endometrial tissue

• Clinical Significance of Ectopic Tissue: The presence of ectopic gastric mucosa is particularly important because it can secrete gastric acid, leading to ulceration of the adjacent ileal mucosa and causing bleeding. GI bleeding may develop due to ulceration within the gastric mucosa or ulceration in the adjacent ileal mucosa.

IV. Differentiation from Alimentary Tract Duplications:

• Location: Alimentary tract duplications, while also congenital anomalies that can occur in the ileum, are typically located on the mesenteric border of the intestine, as opposed to the antimesenteric border for Meckel's diverticulum.
• Meckels are typically solitary. Duplications can occur anywhere along the alimentary tract.

Important Considerations and Additional Information:

• Embryological Basis of Ectopic Tissue: The embryologic origin of ectopic tissue within Meckel's diverticula is not completely understood. Several theories exist, including heterotopic differentiation of pluripotent stem cells during gut development.
• Variations in Presentation: The clinical presentation of Meckel's diverticulum can vary widely depending on the presence and type of ectopic tissue, the size of the diverticulum, and the presence of complications.

B. Clinical Presentation

• A. Asymptomatic vs. Symptomatic:

• Most patients are asymptomatic: Many individuals with a Meckel's diverticulum remain unaware of its presence throughout their lives. The diverticulum is often discovered incidentally during imaging studies or surgery performed for other reasons.
• Approximately 25% become symptomatic: Only a minority of Meckel's diverticula ever cause clinical problems.

• B. Common Clinical Presentations/Complications:

• Painless Lower GI Hemorrhage (Most Common):

• Occurs in up to 50% of symptomatic cases.
• Typically presents as painless rectal bleeding (hematochezia).
• Caused by acid secretion from ectopic gastric mucosa within the diverticulum, leading to ulceration of the adjacent ileal mucosa.
• Bleeding can range from mild and chronic (leading to anemia) to severe and life-threatening.
• More common in children over 2 years of age.

• Meckel's Diverticulitis:

• Occurs in 10%–20% of symptomatic cases.
• Presents with abdominal pain, often in the periumbilical or right lower quadrant region.
• Can be clinically indistinguishable from acute appendicitis, leading to misdiagnosis.
• Caused by obstruction of the diverticulum's lumen, leading to inflammation, necrosis, and potentially perforation.
• Obstruction can be caused by:

• Phytobezoars (e.g., sunflower seeds, pumpkin seeds).
• Enteroliths.
• Foreign bodies (e.g., fish bones, bullets).
• Gallstones.

• Intestinal Obstruction:

• A common presentation, especially in newborns.
• Can occur due to several mechanisms:

• Volvulus: Twisting of the small bowel around a vitelloumbilical (mesodiverticular) cord or band that extends from the diverticulum to the umbilicus. This is especially common in the newborn period.
• Intussusception: The Meckel's diverticulum acts as a lead point, causing telescoping of the ileum into itself.
• Inflammation and Adhesions: Inflammation within the diverticulum can lead to the formation of adhesions, causing bowel obstruction.
• Internal Hernia: Bowel loops can become entrapped under a band or mesentery associated with the diverticulum.
• Bands Between the Diverticulum and Mesentery: Similar to a vitelloumbilical cord, these bands can cause kinking or compression of the bowel.

• Intussusception :

• Especially common in children.
• Can be caused by Meckel diverticulum, serving as the lead point.

• C. Less Common Presentations:

• Neoplasia:

• Very rare in children (0.5%–4% of diverticula).
• Carcinoid tumors are the most common malignancy reported in Meckel's diverticula. Other reported tumors include leiomyosarcomas, lipomas, and adenocarcinomas.
• Tumors are often found incidentally during surgery for other reasons.

• Chronic Peptic Ulceration:

• Rare, usually occurring in the adjacent intestinal mucosa due to acid secretion from ectopic gastric tissue.
• May present with periumbilical or postprandial abdominal pain.

• Perforation:

• Can occur secondary to diverticulitis, ulceration, or foreign body ingestion.
• Presents with signs of peritonitis (abdominal pain, tenderness, guarding, rigidity).

• Umbilical Abnormalities:

• Patent vitelline fistula can present with drainage of bilious or fecal material from the umbilicus, especially in newborns.
• Umbilical sinus or cyst may present as a persistent umbilical discharge or a palpable mass.

• D. Age-Related Differences in Presentation:

• Newborns: Intestinal obstruction is the most common presentation, often due to volvulus or intussusception related to the diverticulum or associated bands.
• Children > 2 years: Painless lower GI bleeding is more common.

• E. Additional Notes:

• Clinical presentation can be quite variable.
• High degree of suspicion is needed, especially in cases of unexplained lower GI bleeding or abdominal pain.
• Meckel's diverticulum should be considered in the differential diagnosis of any child with abdominal pain, intestinal obstruction, or rectal bleeding.

C. Diagnosis of Meckel's Diverticulum in Pediatrics

Diagnosing Meckel's diverticulum preoperatively in children can be challenging, as its clinical and imaging features can mimic other acute abdominal conditions. A tailored approach based on the individual patient's clinical presentation is essential. The absence of lower GI bleeding or stool draining from the umbilicus often makes preoperative diagnosis difficult.

1. Initial Assessment:

• History and Physical Exam: A thorough history and physical exam are crucial. Look for:

• Hematochezia (rectal bleeding).
• Symptoms of chronic iron deficiency anemia.
• Intermittent bowel obstruction.
• Careful examination of the umbilicus for urine, stool, or protruding mucosa, suggesting a patent fistula to the alimentary tract.

• Laboratory Studies:

• Complete blood count (CBC): to evaluate for anemia and infection.
• Coagulation studies: PT/INR, PTT
• Comprehensive metabolic profile
• Type and cross-match for blood transfusion, particularly if bleeding is significant.

• Plain Radiographs (X-rays): Valuable as an initial screening tool. They may reveal:

• Obstruction (dilated loops of bowel, air-fluid levels).
• Free intraperitoneal air (if perforation is suspected).
• Enteroliths (rare).

2. Imaging Modalities:

• Ultrasound (US): Can identify:

• Intestinal obstruction.
• Inflammatory changes.
• Abscess formation.
• Intussusception (target and pseudokidney** sign - see below).
• May identify a cystic structure consistent with an inflamed diverticulum.

• Computed Tomography (CT) Scan: Can identify:

• Intestinal obstruction.
• Inflammatory changes.
• Abscess formation.
• Intussusception.
• The three most common findings associated with Meckel diverticulum are isolated small bowel obstruction, intussusception with small bowel obstruction, and an inflammatory cystic mass.
• May highlight a tubular structure arising from the ileum, suggestive of Meckel's diverticulum with possible inflammation or obstruction.

• Contrast Studies: Seldom diagnostic. While historically used, they are now rarely the primary diagnostic tool.
• Endoscopy (Upper and Lower): Useful for ruling out other sources of bleeding when diagnostic uncertainty exists, but may not visualize Meckel's directly due to its location in the small bowel.

• Capsule endoscopy has been reported in the diagnosis of Meckel's, but is not generally recommended.

3. 99mTc-Pertechnetate Scintigraphy (Meckel Scan):

• Principle: Detects ectopic gastric mucosa within the diverticulum. 99mTc-pertechnetate is avidly taken up by parietal cells of gastric mucosa. (mimics Chloride which actively gets concentrated)
• Technique: Intravenous injection of 99mTc-pertechnetate, followed by serial abdominal images over approximately 60 minutes. A positive scan shows activity in the ectopic gastric mucosa, appearing concurrently with activity in the stomach.
• Location: Most commonly identified in the right lower quadrant, but can appear anywhere in the abdomen.
• Sensitivity and Specificity:

• Sensitivity: Varies, often cited as 60-90%. Wylie text states 60% and the Fellows Review outline mentions 85-90%. A more reasonable overall range is 60-90%, taking into account the factors that can affect it.
• Specificity: Generally high, around 95%. Positive predictive value approaching 100%

• Factors Affecting Sensitivity:

• Inadequate amount of gastric mucosa within the diverticulum.
• Dilution of radiotracer from high bleeding rate.
• Poor blood supply to the diverticulum.
• Active peristalsis distributing RBCs over a substantial length of bowel.

• False Positives:

• Intestinal duplication with heterotopic mucosa.
• Obstructed loops of bowel.
• Intussusception.
• Arteriovenous malformation.
• Ulcers.
• Ureters or bladder activity (typically appears after stomach activity; lateral or oblique views can help differentiate).

• H2-Receptor Antagonists (H2RAs) and Meckel Scan Sensitivity:

• For a Meckel's scan using 99mTc-pertechnetate, pretreatment with H2-receptor antagonists (H2RAs) can enhance the sensitivity of the scan by reducing gastric secretion and increasing tracer uptake in ectopic gastric mucosa. Here's how the prep typically works:

• H2RA Pretreatment Options

• You can use oral (PO) or intravenous (IV) H2RAs, depending on timing and clinical discretion:
• Oral (PO) Regimen

• Start 2 days prior to imaging, Options:

• Cimetidine: 300 mg PO four times daily
• Famotidine: 20 mg PO once daily

• Intravenous (IV) Regimen

• Single dose completed 1 hour before imaging, Options:

• Cimetidine: 300 mg in 100 mL D5W IV over 20 minutes
• Ranitidine: 1 mg/kg IV (max 50 mg) over 20 minutes
• Famotidine: 20 mg IV or 0.25 mg/kg IV

• Notes

• Mechanism of Action: H2RAs work by blocking the action of histamine on the H2 receptors of parietal cells in the stomach. This reduces gastric acid secretion. The key here is that while they reduce the secretion of acid, they do not directly affect the uptake of pertechnetate by the parietal cells.
• Why they are used: The rationale behind using H2RAs is that by reducing the secretion of acid, they allow more of the 99mTc-pertechnetate to be retained within the ectopic gastric mucosa of the Meckel diverticulum, leading to improved visualization on the scan. The pertechnetate is not flushed away as quickly.
• In a way the cimetidine is reducing the amount of “background noise” produced by the stomach.
• Evidence: Multiple studies and guidelines recommend or suggest the use of H2RAs prior to Meckel scanning to improve sensitivity.

4. Diagnostic Laparoscopy/Laparotomy:

• Considered for patients with high clinical suspicion for Meckel's diverticulum and a negative or equivocal Meckel scan, especially if bleeding persists or other complications arise.
• A very safe and sensitive way of screening for Meckel’s diverticulum and other GI or gynecologic pathology, such as congenital bands or endometriosis, when performed by a pediatric surgeon with minimally invasive skills.
• Can directly visualize the diverticulum and allow for surgical resection if indicated.

5. Differential Diagnosis Considerations:

• Alimentary tract duplications (commonly located in the ileum, may contain ectopic gastric tissue, and can cause GI bleeding or obstructive symptoms).
• Intussusception.
• Appendicitis.
• Inflammatory bowel disease (IBD).
• Infectious gastroenteritis.
• Volvulus.
• Other causes of lower GI bleeding (e.g., polyps, fissures).

In summary: The diagnosis of Meckel's diverticulum requires a combination of clinical suspicion, appropriate imaging, and, in some cases, surgical exploration. The Meckel scan remains a valuable tool, but its limitations must be recognized, and other diagnostic options should be considered when the clinical picture is suggestive despite a negative scan. The chosen diagnostic strategy must be tailored to the individual patient.

D. Management and Treatment

• A. Symptomatic Meckel's Diverticulum:

• Surgical Resection is the Standard of Care: Any symptomatic Meckel's diverticulum should be surgically removed.
• Surgical Techniques:

• Diverticulectomy: Excision of the diverticulum at its base. This is appropriate when the diverticulum has a narrow base and no significant inflammation or involvement of the adjacent ileum.
• Segmental Ileal Resection: Removal of the segment of ileum containing the diverticulum. This is preferred when:

• The base of the diverticulum is wide.
• There is significant inflammation, ulceration, or perforation of the adjacent ileum.
• The diverticulum is large.
• There are concerns about the presence of ectopic tissue extending into the adjacent ileum.

• Wedge Resection: A v-shaped excision of the Meckel's diverticulum and the neighboring bowel wall. Typically closed transversely to the axis of the bowel to prevent strictures.

• Surgical Approach:

• Minimally Invasive (Laparoscopic): Generally the preferred approach at tertiary centers with pediatric surgical expertise, when feasible.

• Laparoscopy should be the preferred approach in cases of diagnostic uncertainty, positive Meckel scan, intussusception, and Meckel diverticulitis.
• Can be performed with either extracorporeal (resection performed outside the abdomen after mobilizing the diverticulum) or intracorporeal resection (resection performed entirely within the abdomen using laparoscopic instruments).

• Open Laparotomy: May be indicated in cases of:

• Advanced, high-grade obstruction.
• Perforation with significant peritonitis.
• Unstable patient.
• Situations where laparoscopic approach is not feasible or safe.

• Special Considerations:

• Meckel's Diverticulitis with Abscess: In rare cases, percutaneous drainage of the abscess and parenteral antibiotics may be used as initial treatment to allow the patient to recover and undergo laparoscopic Meckel diverticulectomy once the inflammation has resolved.

• B. Incidental Meckel's Diverticulum:

• Management is Controversial: The decision of whether to remove an incidentally discovered Meckel's diverticulum during surgery for an unrelated condition is a topic of ongoing debate. There are no prospective comparative studies to guide clinical decision-making.
• Arguments for Resection:

• Lifetime Risk of Complications: There is a potential lifetime risk of developing complications from a Meckel's diverticulum (estimated at 4-6%).
• Low Surgical Risk in Stable Patients: The risk of complications from routine resection of a Meckel's diverticulum in a stable pediatric patient is generally low (estimated at 1%). The outline says is 1% versus potential lifetime risk of Meckel complications of 4%–6%

• Arguments Against Resection:

• Unnecessary Surgery: Removing an asymptomatic diverticulum subjects the patient to the risks of surgery (infection, bleeding, anesthesia) without a guaranteed benefit.
• Increased Operative Time: Resection adds to the overall operative time.

• General Recommendations:

• Most pediatric surgeons would recommend the removal of an incidentally discovered Meckel diverticulum in a stable pediatric patient who has received perioperative antibiotics since the life expectancy of a child is long and the risk of surgical complications is extremely low.
• Careful deliberation is needed in certain situations, such as:

• Damage control procedures for trauma.
• Radical resections for cancer.
• Patients with significant comorbidities.

• C. Post-Operative Care:

• Standard post-operative care following intestinal surgery.
• Monitoring for complications such as infection, bleeding, or bowel obstruction.
• Early mobilization and advancement of diet as tolerated.

• D. Importance of Pediatric Surgical Expertise:

• Younger children (especially those younger than 5 years) with a suspected Meckel diverticulum should be referred to pediatric specialty hospitals that routinely take care of children with these types of less common surgical conditions.
• There is strong evidence that children undergoing higher-risk surgical procedures have improved outcomes if their care is provided by pediatric specialists at higher-volume children’s hospitals.

E. Summary:

• The most important factor to remember about Meckel diverticulum is that it may be the troublemaker in any patient who presents with bowel obstruction, lower GI bleeding, umbilical abnormality, or intussusception. The index of suspicion should be highest in children with unexplained lower GI bleeding and kids younger than the age of 4 who present with intestinal obstruction and no prior history of abdominal surgery.

** The "pseudokidney sign" is a term used in radiology, primarily in ultrasound imaging, to describe a specific appearance that can be seen when a segment of bowel is abnormally thickened. It resembles, in cross-section, the appearance of a kidney. Here's a more detailed explanation:

Characteristics of the Pseudokidney Sign:

• Appearance: On ultrasound, the affected bowel segment appears as a hypoechoic (darker) ring surrounding a hyperechoic (brighter) center. This creates a layered appearance that mimics the renal cortex and sinus of a kidney.
• Cause: The sign is caused by thickening of the bowel wall, which is often due to edema, inflammation, or the presence of a mass. The thickened wall forms the outer ring (hypoechoic), while the compressed or edematous lumen of the bowel forms the central area (hyperechoic).
• Significance: The pseudokidney sign is a non-specific finding, meaning it can be associated with a variety of conditions. It suggests the presence of bowel wall thickening, and further investigation is needed to determine the underlying cause.

Common Conditions Associated with the Pseudokidney Sign:

• Intussusception: This is one of the most common and classic associations. The intussusceptum (the segment of bowel that telescopes into the other) forms the pseudokidney appearance.
• Inflammatory Bowel Disease (IBD): Crohn's disease and ulcerative colitis can cause bowel wall thickening and the pseudokidney sign.
• Infectious Colitis: Infections like Clostridium difficile colitis can result in a thickened bowel wall.
• Bowel Wall Hematoma: Bleeding into the bowel wall can cause thickening.
• Bowel Wall Tumors: While less common, tumors can also lead to this sign.
• Edema (e.g., secondary to hypoalbuminemia): Fluid accumulation in the bowel wall can cause thickening.

Important Considerations:

• The pseudokidney sign is not diagnostic in itself. It's an indication of bowel wall thickening, prompting the need for further evaluation to determine the underlying etiology.
• Other imaging modalities, such as CT scans, may be necessary to further characterize the bowel abnormality and rule out other possible causes.
• Clinical context is crucial when interpreting the pseudokidney sign. The patient's symptoms, medical history, and other physical exam findings all contribute to making an accurate diagnosis.

In the context of Meckel's diverticulum, the pseudokidney sign would primarily be relevant if the Meckel's diverticulum were leading to intussusception. In this situation, the ultrasound might show the pseudokidney appearance due to the telescoping of the bowel.