Evaluation of hepatobilliary systems in conjoined twins by ^99mTc-mebrofenin

Sir,

We present a case of 2-month-old conjoined twins with thoracoabdominopagus who were referred for hepatobilliary scintigraphy for evaluation of hepatobilliary function separately for each twin. This study was carried out on twin-A after intravenous injection of 37 MBq ^99mTc-mebrofenin. Dynamic images were acquired, which revealed normal sized liver with good hepatocyte radiotracer extraction in twin-A. Only a faint radiotracer activity was seen in the upper abdomen on uninjected baby [Figure 1a-c]. Same study was performed after injection of the same dose of radiotracer in twin-B. The dynamic images revealed that faint radioactivity region resulted from initial dose administered to first twin became stronger and was proven to belong to hepatic lobes of the second twin. Delayed static image showed fusion of liver with the presence of the tracer and excretions into separate small-bowel loops indicating independent extrahepatic biliary tree drainage in each twin [Figure 1d-f]. The conjoined twins were subsequently separated and both survived the surgery uneventfully.

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Figure 1 ^99mTc-mebrofenin dynamic (a) and static (right lateral, b; left lateral, c) images of the twins lying in the decubitus position as they could not lie down supine. Study revealed good hepatocyte radiotracer extraction in twin-A. After injection of the same dose of radiotracer in twin-B the dynamic (d; arrows) images revealed hepatic lobes of the second twin with delayed static (right lateral, e; left lateral, f; arrows) images revealing fusion of liver and presence of the tracer but excretions into separate small-bowel loops

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Conjoined twins are rare, but the exact prevalence is unknown. The estimated prevalence in the literature varies widely, from 1:50,000 to 1:200,000. Conjoined twins present a unique challenge to pediatric surgeons. Evaluation of crossed circulation is prerequisite in successful surgical separation of conjoined twins. The liver is invariably fused and 25% of thoracopagus twins share a biliary system. Pre-operative evaluation of potentially shared or separate function in conjoined twins is very essential for planning of surgical separation.[12] Demonstration of separate hepatic venous drainage of each twin is especially important, as absent or anomalous hepatic venous drainage in one twin is incompatible with survival after surgery. Radionuclide imaging modalities provide noninvasive and sensitive means for assessment of cross circulation.[3456] There have been few case reports in literatures which shows the role of hepatobilliary scintigraphy in detection of cross circulation in conjoined twins.[7] This is another case which strengthens the importance of ^99mTc-mebrofenin in pre-surgical evaluation of conjoined twins. This case clearly depicts two separate hepatobilliary system in radionuclide imaging, which help the surgeon in separation of twins and improve twins’ survival.