Beyond tumor tracing: physiological uptake of sympathetic ganglia on somatostatin receptor PET/CT - prevalence, patterns, and biological rationale.

Abstract

This study aims to investigate the prevalence, pattern, physiological basis, and influencing factors of sympathetic ganglia uptake on [¹⁸F]AlF-NOTA-LM3 PET/CT. [¹⁸F]AlF-NOTA-LM3 PET/CT images from 101 patients were retrospectively reviewed to evaluate the presence of sympathetic ganglia uptake. Clinical data and normal-organ uptake were investigated to identify influencing factors. Uptake patterns were compared between sympathetic ganglia and metastatic lymph nodes. Immunohistochemical (IHC) staining for SSTR2 was performed on a stellate ganglion and other specimens. Positive sympathetic ganglia were observed in 76.2% (77/101) of patients on [¹⁸F]AlF-NOTA-LM3 PET/CT. 76.2% (77/101), 33.7% (34/101), 23.8% (24/101), 32.7% (33/101) of patients exhibited positive stellate, thoracic, celiac, and sacral ganglia, respectively. Sympathetic ganglia uptake was associated with higher pituitary, adrenal gland, small-intestinal uptake, and lower tumor burden. Sympathetic ganglia generally exhibited a bilateral symmetric distribution and significantly lower uptake than lymph node metastases (SUVmax: 2.29 ± 0.67 vs. 14.52 ± 14.29; P < 0.001). An SUVmax cutoff of 3.45 differentiated sympathetic ganglia from metastatic lymph nodes with an accuracy of 95.9% and an AUC of 0.967. IHC revealed moderate SSTR2 expression in the membrane and cytoplasm of a subset of stellate ganglionic neurons and in neurons of both the myenteric and submucosal plexuses of duodenum. Sympathetic ganglia uptake on SSTR PET/CT is a common physiological finding, featured by symmetric distribution and faint uptake. Histopathology confirming SSTR2-positive ganglionic neurons provides the biological basis for this uptake.