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S. Huynh, M.D., R. Amin, M.D., B. Barron, M.D., R. Dhekne, M.D., P. Nikolaidis, M.D., L. Lamki, M.D.
Texas Houston Medical School and Memorial Hermann - Texas Medical Center (TMC), St. Luke's Episcopal
|INTRODUCTION||GALLERY OF CASES|
Meckel's diverticulum is the most common congenital anomaly of the gastrointestinal tract with a commonly accepted incidence of 2% in the general population. Of these, about 57% contain ectopic gastric mucosa which is responsible for the clinical symptoms. Radionuclide imaging is a primary study for the detection of the ectopic gastric mucosa in a Meckel's diverticulum. Using Tc-99m pertechnetate, which is actively accumulated and secreted by the mucoid cells of the gastric mucosa, there is approximately a 90% detection rate in children and lower in adults. However, there are many false positives associated with these studies. These can be classified as 1.) focal small bowel pathology such as intussusception and Crohn's disease, 2.)neoplasms such as leiomyosarcomas and A-V malformations, 3.) genitourinary causes such as renal pelvis, bladder and uterus, and 4.) ectopic gastric mucosa such as small bowel duplication and duplication cysts. In addition, false positives can be encountered when a Meckel's diverticulum is detected using other nuclear methods such as Tc-RBC and monoclonal antibodies. Examples of such will be exhibited. False negative results can occur from lack of pharmacologic intervention with pentagastrin, cimetidine, or glucagon.
We present a computer-based pictorial essay of the many pitfalls of radionuclide imaging of Meckel's diverticulum. Awareness of these pitfalls and the advantages and disadvantages of the various studies will help the physician interpret the results more effectively. We suggest techniques and the latest advancements to minimize these shortcomings.
Meckel's diverticulum is the vestigial remnant of the omphalomesenteric duct. It is normally located on the antimesenteric border of the terminal ileum within 60 cm of the ileocecal valve and it averages 6 cm in length. About 57% of these contain ectopic gastric mucosa, commonly leading to clinical presentations of peptic ulceration and hemorrhage. Other complications of Meckel's diverticulum include diverticulitis, intussusception, perforation, and obstruction. Most cases that present with these complications require surgery. Although it occurs much more commonly in children, it is an important differential consideration for GI bleed in adults.
99m-Tc pertechnetate is the most common radioisotope used in the detection of Meckel's diverticulum. The usual dose is .2 mCi/kg for children and 10-20 mCi for adults. The pertechnetate anion is taken up by the gastric mucosa whether it is located in the stomach or is ectopic. The lack of ectopic gastric mucosa is the most common cause of false negative scans. On the other hand, any tissue containing ectopic gastric mucosa will take up pertechnetate and is thus a common cause of false positive scans. The use of pharmacologic intervention has been shown to improve the detection of Meckel's diverticula.
FALSE NEGATIVE STUDIES
Meckel's diverticulum has also been reported to be detectable using 99m-Tc sulfur colloid. A case of intussusception secondary to Meckel's diverticulum has been reported from our institution using MN3, which is a Tc-99m labeled antigranulocyte monoclonal antibody under clinical evaluation for the detection of atypical appendicitis.
The use of radionuclide imaging for the detection of ectopic gastric mucosa was first proposed by Harden et al. in 1967 (Harden). The first clinical application was reported by Jewett et al. in 1970 (Jewett). The idea behind 99m-Tc pertechnetate scanning is that the pertechnetate anion is selectively taken up by the surface mucous-secreting cells that line the gastric mucosa (Marsden). Pertechnetate scanning has a reported sensitivity of 80-90% in children, a specificity of 95% and an accuracy of 90% (Sfakianakis, Cooney). In adults, the study is less reliable with a sensitivity 62.5%, a specificity of 9% and an accuracy of 46% (Schwartz). However, most of the data on adults are biased since they are based predominantly on case reports. True positives and negatives are less likely to be included in case reports than false positives and negatives.
Whether imaging children or adults, it is important for both the ordering physicians and the nuclear medicine physicians to be aware of the possible pitfalls involving the Meckel's scan. Knowledge of these pitfalls should allow the radiologists to be more conservative in their impression and not overinterpret equivocal studies. On the other hand, most of the causes of false positive scans are surgical lesions such as intussusception, appendicitis, arteriovenous malformations, and neoplasms. Thus a false positive study is not necessarily of little use.
Most of the causes for a false negative scan are the result of poor technique and are thus avoidable. Awareness of these technical pitfalls is important in performing Meckel's scintigraphy. The technical aspects to keep in mind include the benefits of nasogastric suction, the negative effects of potassium perchlorate and atropine, insufficient radioisotope, delay in imaging, the effects of prior interventions such as laxatives and endoscopy. Perhaps the most overlooked factor in the Meckel's scan are the pharmacologic adjuvants such as pentagastrin, cimetidine, and glucagon. These drugs, if used in the proper setting, can increase the accuracy of the study. Caution should be used in the case of pentagastrin, which can lead to a false negative study due to its washout effects.
As mentioned earlier, 99m-Tc pertechnetate scintigraphy is less reliable in adults than in children. However, there are other options for the detection of suspected Meckel's diverticulum. Antegrade small bowel infusion (enteroclysis) has been described to be successful in the detection of Meckel's diverticulum. Other techniques that are useful include arteriography and Tc-sulfur colloid scans. Meckel's diverticulum may also be detected using MN-3, a Tc-99m labeled antigranulocyte monoclonal antibody. Apparently, MN-3 was able to detect the inflammation of Meckel's diverticula. These studies when combined with pertechnetate scanning should raise the sensitivity of detecting Meckel's diverticula in adults to the pediatric level.
GALLERY OF CASES
1. Anderson GF, Sfakianakis
G, King DR, et al. Hormonal enhancement of technetium-99m pertechnetate uptake
in experimental Meckel's diverticulum. J Pediatr Surg 1980;15:900-4.
2. Barron BJ, Robins DB, Lamki LM, et al. Intussusception secondary to Meckel's diverticulum detection with Tc-99m Monoclonal Antibodies to granulocytes (Leukoscan). Clin Nucl Med 1996;21:834-6.
3. Baum S, dÁvignon MB, Locko RC, et al. Pertechnetate-cimetidine abdominal imaging. Int J Nucl Med Biol 1981;8:185-7.
4. Conway JJ. Radionuclide Diagnosis of Meckel's diverticulum. Gastrointestinal Radiology 1980; 5:209-213.
5. Harden RMcG, Alexander WD, Kennedy I. Isotope uptake and scanning of stomach in man with 99m Tc-pertechnetate. Lancet 1967; 1:1305-7.
6. Hofmeyr NG. Stomach scanning after intravenous 99m technetium adminstration: a preliminary reort. S Afr Med J 1967; 41:572-5.
7. Maglinte DDT, Elmore MF, Isenberg M, et al. Meckel diverticulum: radiologic demonstration by enteroclysis. Am J Radiol 1980; 134:925-32.
8. Maglinte DDT, Jordan LG, van Hove ED, et al. Chronic gastrointestinal bleeding from Meckel's diverticulum: Radiological considerations. J Clin Gastoenterol 1981; 3:47-52.
9. Marsden DS, Alexander C, Yeung P et al. Autoradiographic explanation for the uses of 99m-Tc in gastric scintigraphy. J Nucl Med 1973; 14:632.
10. Ryan JW, Sepahdari S. Detection of Meckel's diverticulum in an infant by Tc-99m-sulfur colloid scintigraphy. Clin Nucl Med 1981 6:193-5.
11. Sfakianakis GN, Anderson GF, King DR. The effect of intestinal hormones of the Tc-99m pertechnetate imaging of ectopic gastric mucosa in experimental Meckel's diverticulum. J Nucl Med 1981; 22:678-83.
12. Siddiqui A, Ryo UY, Pinsky SM. Arteriovenous malformation simulating Meckel's diverticulum on 99mTc-pertechnetate abdominal scintigraphy. Radiology 1977; 122(1):173-4.
Last Modified September 5, 2007