68Ga-PSMA-11 uptake in tracheal mucus plug – a potential pitfall

Abstract

Prostate-specific membrane antigen (PSMA) PET/CT is a well-acclaimed imaging modality for prostate cancer (PCa). However, many reports have highlighted PSMA radioligand uptake in a variety of benign tumors and lesions. We report a case of PCa in which ⁶⁸ Ga-PSMA-11 uptake was noted in the tracheal lumen. However, ¹⁸F-PSMA-1007 PET/CT was done on a subsequent day, which demonstrated no abnormal radiotracer uptake or morphological lesion within the tracheal lumen. This case highlights an uncommon finding of PSMA ligand uptake in a tracheal mucus plug (non-prostatic benign uptake), which may be misinterpreted as a false-positive finding.

PSMA is a transmembrane glycoprotein, which was initially described in PCa cell lines [1]. Currently, small molecule inhibitors that bind to the extracellular domain of the PSMA molecule, such as ⁶⁸ Ga-PSMA-11, are the most frequently used PET tracers for imaging of PCa [2]. Though initially assumed to be specific to the prostate, physiological expression of PSMA has subsequently been reported in the salivary glands, liver, duodenum, colon, kidney, and seminiferous tubules [3–5]. With the increasing adoption of PSMA-targeted PET imaging into clinical practice for the evaluation of PCa, there have been several reports of non-prostatic benign and malignant etiologies showing PSMA radioligand uptake (Figs. 1 and 2). PSMA radioligand uptake has been reported in several benign conditions such as Paget’s disease, fibrous dysplasia, granulomatous diseases (e.g., Sarcoidosis), and benign soft tissue lesions (e.g., hemangiomas, dermatofibromas) [6–10]. PSMA radioligand uptake has also been reported in several non-prostatic cancers (e.g., renal cell carcinoma, lung cancer, hepatocellular carcinomas) [11–13]. Understanding the different physiological variants of radiotracer uptake and the pathological conditions (other than PCa) showing PSMA radioligand uptake is essential for interpretation and adds to the clinical utility of PSMA PET/CT [14, 15]. This case report emphasizes that PSMA radiotracer accumulation can not only occur in the seromucous glands [16] but also in mucus plugs which in the index case was present within the trachea.

Fig. 1.

A 49-year-old male presented with complaints of dysuria and lower urinary tract symptoms for 4 months. On examination, his serum prostate-specific antigen (PSA) value was 19.5 ng/ml. The prostatic biopsy was suggestive of prostate adenocarcinoma, Gleason score (GS) 1 + 4. He underwent ⁶⁸ Ga-PSMA-11 PET/CT for initial staging. The maximum intensity projection (MIP) image (a) demonstrated tracer uptake in the prostatic region (green arrow). Axial PET (b), CT (c), and fused PET/CT (d) images confirmed a tracer avid lesion in the prostate. Apart from the prostatic lesion, focal PSMA ligand uptake (SUV max 9.2) was also noted in the lower neck region (red arrow), which on as transaxial PET (e – black arrow), axial CT (f), and fused PET/CT (g – white arrow) images were localized to fluid density material in the right posterolateral aspect of the tracheal lumen having an average CT Hounsfield unit value of 16, which is consistent with mucus

Fig. 2.

On a subsequent day, the patient underwent whole-body ¹⁸F-PSMA-1007 PET/CT. The MIP image (a) revealed focal PSMA ligand uptake in the pelvis (green arrow), which localized to the prostate on axial PET (b), CT (c), and fused PET/CT images (d). No abnormal PSMA ligand uptake and no discernible morphological change is noted within the tracheal lumen (red arrow in MIP) and PET (e), CT (f), and fused PET/CT images (g), which confirm that ⁶⁸ Ga-PSMA-11 uptake in the tracheal lumen 1 day before was a mucus plug in the trachea. On further history, examination of the patient confirmed that he had a productive cough for the past 1 week

Declarations

Conflict of Interest

Kunal Ramesh Chandekar, Apurva Sood, Rajender Kumar, Harmandeep Singh, and Shrawan Kumar Singh declare that they have no conflict of interest.

Ethical Approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and /or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. For this type of study, formal consent is not required.

Informed Consent

The institutional review board of our institute approved this retrospective study, and the requirement to obtain informed consent was waived.