Unexpected Splenic and Retroperitoneal Uptake on Technetium-99m Pyrophosphate (Tc-99m PYP) Imaging: Expanding the Spectrum of Extracardiac Findings

The diagnosis of transthyretin cardiac amyloidosis (ATTR-CA) remains challenging. Extracardiac uptake of technetium-99m pyrophosphate (Tc-99m PYP) is less understood and may provide insights into other underlying conditions. This report presents a rare case of extracardiac Tc-99m PYP uptake in a patient with retroperitoneal hemorrhage. A 55-year-old female patient with no history of coagulopathy or anticoagulant use presented with left flank and abdominal pain. Contrast tomography imaging of the abdomen and pelvis revealed a large left retroperitoneal hematoma of unknown etiology. Consequently, a Tc-99m PYP scan was performed the following day to assess for cardiac amyloidosis. However, several incidental findings were observed, including increased tracer uptake in the spleen and a large area in the left upper abdomen corresponding to an actively bleeding retroperitoneal hematoma. The presence of splenic uptake has been associated with AL cardiac amyloidosis (AL-CA). Extracardiac Tc-99m PYP uptake should be incorporated into image interpretation to enhance diagnostic accuracy, inform treatment planning, and improve prognostic assessment. However, the clinical meaning of extracardiac uptake is not fully established, emphasizing the importance of future research to better delineate its role in identifying amyloidosis and other systemic disorders.