Equis ISSN 2398-2977

Portosystemic shunt: scintigraphy

Synonym(s): Portosystemic shunt imaging

Contributor(s): Russel Malton, Rachel Murray

Introduction

  • When administered in high concentration per rectum, a proportion of  99mTc-pertechnetate is rapidly absorbed across the colonic mucosa.
  • Its normal transit through the portal vessels to the liver and shortly thereafter the heart can be imaged by dynamic scintigraphic studies.
  • 99mTc-pertechnetate is not actively taken up by the liver or heart and the study is therefore essentially a nuclear angiogram of the portal system.
  • The normal time delay between detection of the radiopharmaceutical in the liver and heart is related to patient size.  When portosystemic shunting is present, some of the administered radiopharmaceutical reaches the heart at the same time as, or before, it is detected in the liver.
  • During the first pass of 99mTc-pertechnetate, the ratio of integrated heart to liver counts can be used to estimate the percentage of portal blood flow which has bypassed the liver through the shunt.

Radiopharmaceutical

  • 99mTc-pertechnetate  (99mTcO4-).

Dosage

  • 37-74 MBq/kg has been used in small animals and is suggested as a guideline for dosage in foals. As less than 15% is initially absorbed through the colonic mucosa, the dose should be concentrated in 1-2 ml saline.

Uses

  • This is a simple and inexpensive screening test for the presence of  a portosystemic shunt and may be indicated in foals where more common causes of neurological abnormalities such as trauma, vertebral body abscesses, brain abscesses and meningitis, have been ruled out.
  • Estimation of the degree of shunting by calculating the shunt fraction.
  • Follow up evaluation of  surgical  intervention by comparison of pre and post-operative shunt fraction calculations. The comparison may not be reliable because of interstudy variability.

Requirements

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Preparation

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Procedure

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Aftercare

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Samii V F, Kyles A E, Long C D et al (2001) Evaluation of interoperator variance in shunt fraction calculation after transcolonic scintigraphy for diagnosis of portosystemic shunts in dogs and cats. JAVMA 218 (7), 1116-1119 PubMed.
  • Daniel G B, Bright R, Ollis P et al (1991) Per-rectal portal scintigraphy using 99mTechnetium pertechnetate to diagnose portosystemic shunts in dogs and cats. J Vet Intern Med 5 (1), 23-27 PubMed.
  • Buonanno A M, Carlson G P, Kantrowitz B (1988) Clinical and diagnostic features of portosystemic shunt in a foal. JAVMA 192 (3), 387-389 PubMed.
  • Lindsay W A, Ryder J K, Beck K A et al (1988) Hepatic encephalopathy caused by a portocaval shunt in a foal. Vet Med 83 (8), 798 VetMedResource.

Other sources of information

  • Koblik P D, Hornof W J (1996)Portosystemic shunt imaging.In:Handbook of Veterinary Nuclear Medicine. Eds: Berry C R & Daniel G B. North Carolina State University, Raleigh, NC, USA. pp 97-105.


ADDED