Promising role of single photon emission computed tomography/computed tomography in Meckel's scan

INTRODUCTION

Meckel's diverticulum occurs in about 2% of population with young male preponderance and common clinical presentation being painless bleed per rectum (P/R). In most of these cases ectopic gastric mucosa with or without associated ulceration can be demonstrated in the diverticulum.[1] Tc-99m pertechnetate scan is a commonly performed procedure for detection of Meckel's diverticulum. We present the usefulness of single-photon emission computed tomography/computed tomography (SPECT/CT) co-registration that helps in better localization of the pathology.

CASE REPORTS

Case 1

A 10-year-old male presented on 16/02/12 with 3 months history of abdominal pain and episodes of bleeding (P/R). Upper upper gastrointestinal (GI) endoscopy (UGIE) and colonoscopy was carried out and was normal. Routine blood investigation revealed anemia (Hb = 7.9 Gm%). He was hospitalized for recurrent symptoms. His presentation suggested an obscure-overt source of GI bleeding. Meckel's scan was carried out and dynamic as well as static images were acquired. Initial images does not reveal any abnormal focus of tracer uptake, However, in view of clinical presentation strongly suggesting heterotopic gastric mucosal location, delayed static views at 60 min were acquired, which showed a focus of tracer uptake in the mid line of lower abdomen [Figure 1]. Furthermore, fused SPECT-CT imaging showed focal uptake in the distal ileum [Figures 2 and 3]. The patient underwent Meckel's diverticulectomy with sparing of adjacent bowel. Histopathology confirmed the heterotopic location of gastric mucosa [Figure 4].

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Figure 1 Static anterior and posterior images of case 1 shows one focus of intense tracer uptake in the left upper quadrant, corresponding to normal gastric uptake, and a second focus of intense uptake localizing to the right lower quadrant, suspicious for Meckel's diverticulum

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Figure 2 Meckel's scan images are fused with axial and single photon emission computed tomography images to localize and define the abnormality responsible for the positive Meckel's scan. In the right lower quadrant near the ileum a focus of intense uptake localized to the terminal ileum, consistent with a Meckel's diverticulum

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Figure 3 Coronal section of single photon emission computed tomography/ computed tomography and SPECT of case 1 showing focus of increased tracer uptake in the pelvis region on the right side consistent with ectopic gastric mucosa location

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Figure 4 Post diverticulectomy of case 1 histology confirms heterotopic location of gastric mucosa

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Case 2

A 3.5-year-old male presented on 18/05/12 with complaints of two episodes of passage of clots in stools in past 7 days associated with episodic colicky pain abdomen and vomiting. There was similar episode of bleeding P/R in Feb 2012, which was treated as dysentery. Complete blood count showed anemia (Hb = 5.1 Gm%). Patient was hospitalized and 2 units of blood were transfused. Colonoscopy revealed blood clots until the splenic flexure of colon and no other pathology. Meckel's scan was carried out and dynamic as well as static images were acquired. A focus of intense tracer uptake in the right paramedian lower abdomen was seen. Fused SPECT/CT images showed malrotated ectopic kidney in the same location [Figures 5 and 6]. Thus, the study was negative for Ectopic gastric mucosa. Video colonoscopy commented a doubtful lesion in the terminal ilieum,? Koch's. ultrasongraphy abdomen was normal, except malrotated left kidney. Patient was advised review after 3 months.

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Figure 5 Axial single photon emission computed tomography/computed tomography of case 2 showing focal uptake in the pelvicalyceal system (PCS) of ectopic right kidney

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Figure 6 Coronal section of case 2 showing focal uptake in the PCS of ectopic right kidney and left renal fossa without kidney

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DISCUSSION

Five percent of patients with overt GI bleeding have a small bowel source between the ligament of Treitz and the ileocecal valve designated as obscure (negative UGIE and colonoscopy). Meckel's diverticulum occurs in about 2% of population with young male preponderance and common clinical presentation being painless bleed P/R. In most of these cases, ectopic gastric mucosa with or without associated ulceration can be demonstrated in the diverticulum.[1] Meckel's diverticulum, first described by Fabricius Hildanus in 1598, is a 1-11 cm remnant of the embryonic omphalomesenteric duct situated 40-130 cm from the ileocecal valve. This congenital variant poses a 4% lifetime risk of becoming symptomatic with GI bleeding, inflammation or obstruction. Classically, children present more commonly with GI bleeding and adults develop obstruction. Obstruction more commonly arises by (i) entanglement of the small bowel around a fibrous cord extending from the diverticulum to the umbilicus, abdominal wall or viscera, but (ii) may also occur in the free and unattached diverticulum by intussusception with the diverticulum serving as the lead point or (iii) obstruction of Meckel's diverticulum by a fecolith with diverticulitis causing inflammation and adhesions.[2]

The Meckel's scan involves planar, scintigraphic detection of Tc-99m pertechnetate, an anion, which is intravenously infused and selectively taken up by mucous secreting cells lining gastric and ectopic gastric mucosa. Ectopic mucosa is present in ~50%, of which 60% contain gastric mucosa, which increases to 90% of bleeding Meckel's diverticula.[3] Diagnostic accuracy of the Meckel's scan is > 90% in the pediatric population, but is less accurate in adults.[4] The scan can be false positive in various conditions [Table 1]. Fused with SPECT/CT imaging may help in better visualization of Meckel's diverticulum and rule out other causes for abdominal pain and bleeding.[56]

Table 1 Causes of a false-positive Meckel's scan

CONCLUSION

The value of SPECT/CT with co-registered (fused) images is that the precise anatomic location of a focus of uptake can be ascertained. This can potentially eliminate false-positive Meckel's scans, enhancing the diagnostic accuracy of the scan. In a negative scan, the CT images can help to identify other causes of abdominal pain and bleeding. Meckel's scan along with SPECT/CT co-registered imaging should always be considered to optimize the diagnosis of cause of GI bleed, abdominal pain, and localization of Meckel's diverticulum.