Meckel's Scan

 

• Most common congenital anomaly of GI tract (INCIDENCE – 1 to 3% of general population).
• Most common cause of lower gastrointestinal haemorrhage in previously healthy infants.

• Vestigial remnant of the omphalomesenteric duct.

• Location – Anti-mesenteric border of the terminal ileum within 80–100 cm of the ileocecal valve. 
  
•  Approximately 57% of Meckel diverticula contain heterotopic gastric mucosa -secretes HCL.
• Most common sign of Meckel diverticulum is gross rectal bleeding.
• ^99mTc-pertechnetate is taken up by the mucin-producing cells of gastric mucosa and is then secreted into the gut lumen.
• Overall sensitivity of 85%, specificity of 95%, and accuracy of 90%. 

• CLINICAL INDICATIONS:
• To localize heterotopic gastric mucosa in a Meckel diverticulum as the source of unexplained GI bleeding.
• When patient is not actively bleeding – Meckel scintigraphy.
• Active bleeding -radiolabelled red blood cell (RBC) scintigraphy.

• PROCEDURE:
• Rule out recent in vivo RBC labelling, recent barium studies, colonoscopy and use of laxatives.
• Fasting of 3–4 h.
• Ensure voiding before study and and at the end before imaging.
• Histamine H2 blockers, Proton pump inhibitors, Glucagon (TO IMPROVE SENSITIVITY)
• 99mTc-pertechnetate is injected IV.
• Recommended dose
•               Children - 0.05 mCi/kg  (minimum – 0.25 mCi)
•               Adults - 8–12 mCi

• ACQUISION PROTOCOL:
• Supine position
• Imaging field – abdomen and pelvis (to include stomach and bladder)
• Children – thorax should be included
• Anterior abdominal dynamic flow images
• 1–5 s/frame for up to 1min, 30-60s per frame for 30-60 min
• Static images (anterior, anterior oblique, lateral, and posterior projection views) are recommended at the end of the dynamic acquisition.
• SPECT CT may improve the detection of 
•                     - small diverticulum.
•                     - diverticulum obscured by the urinary bladder.
•                     -clinical suspicion for a Meckel diverticulum is high and the planar images have negative or equivocal findings.

• MECKEL'S SCAN
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• Normal uptake in flow phase – heart, lung, major vessels, liver, spleen, kidney, ureter and bladder.
• Stomach activity appears early on dynamic scintigraphy and is most prominent after 10–15 min.
• Ectopic gastric mucosa is visible as a focal, localized area of uptake that appears at the same time as the activity in the normal gastric mucosa.
• Most common location – right lower quadrant.
• A four year old child presented with recurrent episodes of pain abdomen around the umbilicus associated with passage of fresh blood per rectum off and on for the last one and half years.
• Prominent gastric activity appearing at approximately 15 min in the left upper quadrant.
• Small round area of intense tracer activity in the right lower quadrant of abdomen suggesting the presence of ectopic gastric mucosa.
• Exploratory laparotomy which confirmed the presence of Meckel’s diverticulum.
• Diverticulectomy with end to end anastomosis.

• FALSE POSITIVE:
• Tracer activity in the proximal small bowel, kidneys, ureter, or bladder is mistaken for ectopic gastric mucosa.
• Duplication cyst with ectopic gastric mucosa
• Bowel inflammation 
• Intussusception or small-bowel obstruction 
• Peptic ulcer 
• Vascular lesions with increased blood pool (hemangioma or AV malformation)

• FALSE NEGATIVE:
• 1. Procedures that may cause interference
•                     - barium fluoroscopy, administration of perchlorate.
• 2. Anatomic or physiologic causes of errors – when image is obscured by
•                     - brisk GI bleeding
•                     - by the urinary bladder or dilated ureter
•                     - focus of ectopic mucosa is small (1.8 cm 2)
•                     - if there is movement of the diverticulum

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