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Marshfield Clinic and Marshfield Medical Research Foundation Marshfield, WI 54449
We read with interest the recent article, "Gallium Uptake in
Complicated Pancreatitis: A Predictor of Infection"
[1]. It presents a difficult
clinical situation. No test is as sensitive, specific, or accurate as one
would like. In nuclear medicine, another test is almost always on our list of
possible examinations, and gallium-67 citrate scans are no exception. In this
case, 111In-labeled WBC or 99mTc-labeled
hexamethylpropyleneamine oxime (HMPAO) WBC scans offer another view of
inflammatory
processes.
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We had a case in which a 52-year-old man had repeated bouts of pancreatitis and multiple abdominal surgeries. He presented to us for infection localization with an elevated WBC and fever of unknown cause. On CT, we could not differentiate chronic from acute-on-chronic pancreatitis, but we identified a fluid collection in the anterior abdominal wall that could represent a sterile or infected abscess. An 111In-labeled WBC scan was ordered, and the planar images showed activity in the region of the pancreas. Single-photon emission computed tomography (SPECT) images more clearly revealed the activity in the pancreatic bed. After the patient was treated for a pancreatic abscess, his signs and symptoms improved.
Although little has been published on the subject, our search of the literature yielded mixed results. An article by Myerson et al. [2] reported that gallium localized both pancreatic infection and necrosis, unlike the findings of the present study [1]. Aburano et al. [3] showed diffuse pancreatic activity in acute pancreatitis, resulting in an inconsistent positive finding.
Gallium-67 citrate or 111In-labeled WBC with medium-energy photons and a low injected activity do not make ideal SPECT imaging agents, but 99mTc-labeled HMPAO WBC does, as long as imaging is performed before gut activity begins. We typically begin imaging the abdomen 2 hr after injection to avoid this problem. 99mTc-labeled HMPAO WBC may present the most time-efficient method of nuclear imaging until WBC antibodies become available.
References
Shands Hospital and University of Florida College of Medicine Gainesville, FL 32610-0374
For years I have used a somewhat fractured colloquialism: "There is more than one way to nuke a cat." The list of radionuclide infection-imaging techniques is quite long, and includes gallium-67 imaging, WBC imaging (111In-labeled WBC or 99mTc-labeled hexamethylpropyleneamine oxime WBC), indium chloride imaging, monoclonal antibodies to WBC, nonspecific IgG, FDG, 99mTc nanocolloid, to name just a few. I have preferred gallium for several reasons: it doesn't require handling of blood in the laboratory; it is inexpensive; when it is kept on hand, results can be made available in as short a time as 4–24 hr; and it is good for both acute and chronic infections.
The value of radiolabeled WBC versus gallium for chronic infection has been debated for a long time. Sfakianakis et al. [1] published a report comparing gallium and WBC imaging for acute versus chronic infection and found that gallium was better than WBC imaging in this regard. Many articles in the literature support both sides of the argument, but my clinical experience has always mirrored the findings of Sfakianakis et al. WBC imaging is less than perfect. It clearly fails us in vertebral osteomyelitis (whether acute or chronic), and it has problems in a number of settings. Figure 2 shows a problem case.
In our population of patients with complicated pancreatitis, it is not unusual to find remote infection as the cause for fevers or elevated WBC. 99mTc WBC scans are problematic in the lung (normal lung activity is shown in Figure 2A), whereas gallium lung uptake is much easier to interpret. Figure 3A shows a large pancreatic phlegmon without significant gallium uptake, and Figure 3B shows an unexpected right basilar pneumonia. (Chest radiographic and CT findings were interpreted as compression atelectasis.)
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I am a gallium guy. I have continued to use gallium over decades in a number of settings, including workups for fever of unknown origin; diagnosis and follow-up of osteomyelitis, including the differentiation of malignant otitis externa from temporal osteomyelitis; spinal infections; and in the evaluation of the diabetic foot. Gallium SPECT is of lower imaging quality than technetium SPECT, but as our illustrations show, diagnostic-quality gallium SPECT images can be routinely obtained with any well-tuned, modern SPECT system, whereas the limited dose of 111In-labeled WBC is not as easy to image with SPECT.
We have shown the value of gallium SPECT in determining the infectious status of fluid collections in severe pancreatitis [2]. 99mTc WBC may well provide similar results, but this should be shown, not speculated. I would be pleased to read about a series of cases in addition to the report of a single case. I believe that the most important message is that nuclear imaging can play a role in the evaluation of pancreatic fluid collections and that gallium is still a viable choice, but if gallium is used, SPECT must be performed and directly correlated with CT.
Again, there is more than one way to nuke a cat.
References
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