Technetium Scans and Meckel’s Diverticulum

ABSTRACT & COMMENTARY

Synopsis: Technetium-99 "Meckel’s scans" have a relatively low predictive value and may result in the need for operative evaluation despite negative scan results. Exploratory laparotomy or laparoscopy may be indicated instead of scintigraphic scanning in an anemic pediatric patient with lower GI bleeding, especially inpatients in whom there is a high clinical suspicion for a bleeding Meckel’s diverticulum.

Source: Swaniker F, et al. The utility of technetium 99m pertechnetate scintigraphy in the evaluation of patients with Meckel’s diverticulum. J Pediatr Surg 1999;34:760-765.

Fresca swaniker and associates from the Department of Surgery of the C.S. Mott Children’s Hospital of the University of Michigan Medical Center conducted a 22-year retrospective study that evaluated the records of 235 consecutive pediatric patients who had either a Meckel’s scan (n = 165) or had a discharge diagnosis of Meckel’s diverticulum (n = 70). In all patients, the Meckel’s scan had a positive and negative predictive value of 0.93. However, in patients with lower GI bleeding and a hemoglobin less than 11.0 gm/dL, the scan had a sensitivity of 0.60, a positive predictive value of 1.0, but only a negative predictive value of 0.74. Thus, the probability that a child who presents with lower GI bleeding and a hemoglobin less than 11.0 gm/dL will have a Meckel’s diverticulum despite a negative scan is 26%. Eight patients with a false negative scan were found to have Meckel’s diverticuli containing ectopic gastric mucosa at surgery. Clinical impressions had a major effect on the decision-making process in these patients, despite the results of the scan. The relatively low negative predictive value of the Meckel’s scan may result in a need to consider surgery, despite a negative scan result. These findings suggest that surgical exploration may be indicated instead of scintigraphic scanning in the assessment of the anemic pediatric patient with lower GI bleeding, especially in patients in whom there is high clinical suspicion for a bleeding Meckel’s diverticulum.

Comment by Dana Schwartz, MD

In most instances, Meckel’s diverticuli are asymptomatic and incidentally found at surgery or autopsy. However, in symptomatic patients who present with lower GI bleeding or bowel obstruction, the diagnosis is often made after much difficulty. Both clinical and radiologic examinations are often nondiagnostic. In one series, only 6% of patients were diagnosed preoperatively.1

The aim of the present study was to assess the use of technetium (Tc) 99m pertechnetate scintigraphy (Meckel’s scan) in the diagnostic workup of the pediatric patient with GI bleeding and a suspected Meckel’s diverticulum. This study is performed retrospectively over a 22-year period. A subclass of patients—those with lower GI bleeding and a hemoglobin level of less than 11.0 g/dL who underwent a Meckel’s scan—were assessed for use of the scan. Swaniker et al conclude that the scan has a high positive and negative predictive value for all patients with a suspected Meckel’s diverticulum, but that the negative predictive value for this important subclass of patients was too low at 0.74 and, therefore, the use of the scan in such patients is compromised. Therefore, they advocate the addition of "minimally invasive laparoscopy," or exploratory laparotomy, instead of nuclear medicine imaging, to the diagnostic algorithm of identifying the presence of a bleeding Meckel’s diverticulum in the evaluation of pediatric patients with clinically significant GI bleeding and a high index of suspicion for a bleeding Meckel’s diverticulum.

This study did take place over a relatively long period, given the rapidly evolving technology present in all branches of medicine. The sensitivity and specificity of a Meckel’s scan may be increased by the use of pentagastrin stimulation and ranitidine (H2-receptor antagonist), used individually or together. Although some of the negative scans in the present study were repeated following the addition of pentagastrin alone, the false negative rate did not change significantly. However, the addition of single photon emission computed tomography (SPECT) imaging may further increase the detection of a small Meckel’s diverticulum by precisely depicting the radionuclide distribution within a small volume of tissue.2 SPECT is analogous to CT and MR in that multiplanar imaging is obtained and displayed as thin sections. SPECT improves anatomic resolution by enhancing the contrast between focal, vascular, and soft tissue uptake of the pertechnetate.

An additional dilemma in the diagnosis of Meckel’s diverticuli with ectopic gastric mucosa is related to the size of the diverticulum. When planar scintigraphic imaging is used, it is generally accepted that gastric mucosa of 1 cm2 is required for proper identification. It is unclear if SPECT is able to detect even smaller volumes. Swaniker et al do not describe the sizes of the lesions resected in the present cases; perhaps only the smaller lesions were missed.

For most children, no anesthesia or sedation is required for nuclear medicine imaging as long as the child can be safely restrained for the duration of the study. The same is not true for any operative procedure.

In general, the diagnosis of Meckel’s diverticulum with ectopic gastric mucosa continues to be a difficult one, often only established after the exclusion of other entities. The use of Tc 99m-pertechnetate continues to be a sensitive and specific test (85-90% and 95%, respectively) with a reported accuracy of 90-98%. Improving technology may improve these numbers in the future. When clinically indicated, however, an operative procedure may be necessary to identify a small, bleeding diverticulum. (Dr. Schwartz is Associate Professor of Diagnostic Radiology [Pediatrics] at the Yale University School of Medicine.)

References

1. Yamaguchi M, et al. Meckel’s diverticulum: Investigation of 600 patients in Japanese literature. Am J Surg 1978;136:247-248.

2. Connolly J, et al. Meckel’s diverticulum: Investigation of heterotopic gastric mucosa with technitium 99m pertechnate SPECT. J Nucl Med 1998;39:1458-1459.

Technitium 99m pertechnate scans in the diagnosis of Meckel’s diverticula:

a. have a low positive predictive value in the diagnosis of a bleeding Meckel’s diverticulum.

b. according to the literature, their sensitivity may be increased with the use of pentagastrin.

c. can regularly detect intradiverticular gastric mucosa less than 1 cm in diameter.

d. when negative, operative intervention is unnecessary.