Abnormally high diffuse activity on bone scintigram. The importance of exposure time for its recognition

Technical note: identifying the prostate cancer 'superscan' by quantitative skeletal scintigraphy

AIM

The risk of failing to recognize the false, normal pattern of the superscan is a real one, with potential consequences for diagnosis and treatment. Quantitative indices of bone activity have previously measured uptake ratios or exposure time. Such estimates from spot images have provided differentiation of the superscan from normal. More recent reports describe quantitative methods for scanning type gamma-cameras, relying upon significant computation, availability of image analysis programmes or the drawing of whole skeletal regions of interest. The aim of this study was to establish a set of reference values for the evaluation of skeletal scintigraphy images, using the whole-body count alone.

MATERIALS AND METHODS

Patients underwent a routine whole-body bone study using the scanning technique. The total counts acquired during the scan were used to compare the skeletal uptake of the radiopharmaceutical between prostate patients showing superscan image patterns (n=38), prostate cancer patients with normal scans (n=40) and a control group (n=40) with normal scans, referred for reasons other than prostate cancer.

RESULTS

Qualitative comparison showed patterns of avid bone uptake with diminished visualization of kidney and bladder activity in the superscan group, and normal scans in the control and prostate patient groups. Quantitation using total counts recorded directly from the whole-body bone scan showed a significantly raised value in the superscan group only (P<0.001). We have established a simple set of objective reference bands to complement visual interpretation of the scan.

CONCLUSION

The whole-body image count alone, with little or no additional processing, is a helpful discriminator for the nuclear medicine superscan. This may assist the identification of this relatively uncommon diffuse metastatic disease in men with prostate cancer and reduce the number of investigations that might otherwise be reported incorrectly as normal.

An unusual alkaline phosphatase isoenzyme associated with gastric carcinoma

We describe a 50-year-old man with a diagnosis of gastric carcinoma made on gastroscopy after X-rays of the thoracolumbar spine had revealed multiple lytic metastases. A bone marrow aspirate showed adenocarcinoma cells. Polyacrylamide gel electrophoresis incorporating wheat germ lectin was used to separate the serum alkaline phosphatase isoenzymes. Isoenzyme separation showed a markedly increased amount of bone isoenzyme, a normal amount of liver isoenzyme and a considerable amount of an intestinal-like isoenzyme running cathodic to the bone isoenzyme. There was also some immunoglobulin-complexed alkaline phosphatase, which, when digested, showed more of the intestinal-like isoenzyme. This was a variant alkaline phosphatase isoenzyme found in a patient with a gastric carcinoma with a super bone scan. There have been two previous reports of patients with a variant alkaline phosphatase isoenzyme and a super bone-scan.

Recording of bone marrow activity in liver-spleen (RES) scintigraphy

The bone marrow activity in the liver-spleen (RES) scintigraphy has been difficult to estimate correctly. If the activity of the bone marrow is to be decided as counts/time unit it is of importance that structures with a high activity as the liver and spleen are excluded from the registration. A dorsal registration of the pelvis during 180 s will give a rather correct information of bone marrow activity and besides an image of the pelvic bone marrow is obtained. Using 270 to 280 MBq 99Tcm-Albures all 45 normal cases had values below 150 KCNT (1 KCNT = 1 000 counts). All cases with cirrhosis (n = 15) or metastases in the liver (n = 14) had values over 150 KCNT. Values over 150 KCNT were also found in 29 of 34 patients with an increase in ASAT and ALAT (GOT, GPT) as the only pathologic finding and in 12 of 21 patients with a carcinoma but without metastases in the liver.