Usefulness of Tc99m HMPAO Labeled Leukocyte Scintigraphy in differentiating Splenic Abscess from Infarct

摘要

Radionuclide labeled leukocyte studies are routinely performed in the evaluation of patients with fever of unknown origin and occult infections. Cerebral perfusion agent Tc99m hexamethylpropyleneamine oxime (Tc99m — HMPAO) is one of the radiopharmaceuticals widely used for labeling of mixed leukocytes. It is a lipophilic agent which crosses cell membranes readily and preferentially labels granulocytes. This mechanism is used for labeling of leukocytes. Tc99m labeled leukocytes normally accumulate in spleen by sequestration. At sites of acute infection, focal increased radiotracer labeled leukocyte uptake is seen. Hence, focal defects in spleen represent infarcts. We present in this report two cases of splenic infarct diagnosed by Tc99m HMPAO labeled leukocytes. Introduction Tc99m HMPAO labeled leukocytes accumulate in foci of acute infectious processes. Acute pyrogenic infections are usually associated with elevated neutrophil counts. Various infections that localize radiolabeled leukocytes include osteomyelitis and other orthopedic infections as well as intra abdominal, renal, cardiovascular and pulmonary infections. Since the introduction of labeling of leukocytes by Tc99m HMPAO by Peters et al (1) till now, it has also proven very efficacious in the evaluation of occult infectious processes. In addition, Tc99m HMPAO labeled leukocytes play an important role in the diagnosis of non-infectious etiology of fever of unknown origin. Use of Tc99m HMPAO in the evaluation of cerebral infarcts is well known. Here we present two cases of splenic infarct diagnosed by Tc99m HMPAO labeled leukocytes. Materials And Methods Leukocyte labeling and Imaging techniquesLeukocyte labeling of Tc99m HMPAO is performed using standard labeling methods (1,2,3). 10mci of Tc99m HMPAO labeled leukocytes were injected intravenously. Whole body and spot images were obtained at 4 and 24 hours using a GE dual head gamma camera equipped with a low energy high resolution collimator with 140 keV and a 15 % window. Case Illustrations Case 141 y/o paraplegic male presented with sepsis and fever of unknown origin. A Computed tomography (CT) of the abdomen demonstrated a multiple hypodense lesions throughout the spleen likely representing abscesses. A follow-up ultrasound indicated intrasplenic infarction with a hematoma, necrotic tissue and/or infected collection. A radiolabeled leukocyte study was requested to differentiate an abscess versus infarct in the spleen.Case 2A 37 y/o male status post pancreas renal transplant presented with fever. A CT scan reported a peripheral hypodensity in the posterior spleen suspicious for infection or an infarct. A radiolabeled leukocyte study was requested to localize the source of infection.