The introduction of SST analogues (DOTATOC, DOTATATE, DOTANOC) labeled with ⁶⁸gallium (⁶⁸Ga) as radiopharmaceuticals for PET has been used successfully for the diagnosis and therapy management of SST-expressing tumors, emphasizing the high sensitivity and specificity of NETs compared to SSTR scintigraphy and diagnostic CT [14].

A recent publication of our group compared both ⁶⁸Ga-DOTATOC PET and¹⁸F-DOPA PET with diagnostic CT, observing a detection rate of 100 % for both functional imaging modalities in nonmetastatic glomus tumors [15]. However, in metastatic disease the per-lesion rate of ¹⁸F-DOPA PET was lower compared to ⁶⁸Ga-DOTATOC PET (56 % versus 100 %, respectively), taking into account that foremost bone lesions, verified by both ⁶⁸Ga-DOTATOC PET and diagnostic CT, were ¹⁸F-DOPA negative [15] (Figs. 15.2 and 15.3).

Recent publications and case reports confirmed the high detection rate of somatostatin receptor PET/CT in HNPGL, demonstrating the high diagnostic accuracy of ⁶⁸Ga-DOTANOC PET/CT compared to ¹³¹I-MIBG scintigraphy and even to conventional imaging (CT or MRI), including distant metastases [16, 17]. This is in line with previous publication of our group, comparing ¹²³I-MIBG scintigraphy including SPECT/CT to ⁶⁸Ga-DOTATOC PET/CT in patients with glomus tumors [18] (Figs. 15.4 and 15.5). Thereby, all head and neck manifestations were verified by both diagnostic CT and ⁶⁸Ga-DOTATOC PET compared to ¹²³I-MIBG SPECT/CT, which detected only one out of 17 positive ⁶⁸Ga-DOTATOC PET/CT lesions. Additionally, all distant metastases (e.g., the abdomen, bone) were verified by ⁶⁸Ga-DOTATOC PET/CT, providing the accurate tumor extent of patients with extra-adrenal PGL, compared to ¹²³I-MIBG scintigraphy, including SPECT/CT [18] (Figs. 15.4 and 15.5). To explain this on a molecular level, it has been suggested that extra-adrenal PGL could undergo dedifferentiation, leading to a loss of norepinephrine transporter or vesicular monoamine transporter (VMAT), which could then lead to false-negative ¹²³I-MIBG scintigraphy findings in metastatic disease [19]. In contrast to the excellence of ¹²³I-MIBG imaging in the detection of primary sympathetic PGL, its sensitivity is low in parasympathetic HNPGL [20]. Fottner et al. suggested that this could result from the under-expression of VMAT-1 in HNPGL [21]. Although ¹¹¹In-pentetreotide scintigraphy shows high sensitivity in HNPGL [8], as mentioned above, it is limited in detecting PGL lesions of sympathetic origin and – additionally – limited by its lower spatial resolution compared to PET [10].