By Klaas Pieter Koopmans, MD, UMCG Groningen and Partha Ghosh, MD, Siemens Healthineers
Data and images courtesy of EMC Grha Kedoya Hospital, Jakarta, Indonesia
History
65-year-old man with history of colon carcinoma treated with chemotherapy followed by colonic resection surgery in December 2025. Immunotherapy started in January 2026 and the patient was referred for Fludeoxyglucose F 18 injection (18F-FDG) PET/CT study to evaluate tumor response.
Study was acquired 60 minutes following intravenous injection of 4.4 mCi (163 MBq)** 18F-FDG (0.05 mCi/kg or 1.85 MBq/kg)) on the the Biograph Vision Quadra 106 cm long axial field of view (LAFOV) PET/CT. Total scan time was approximately 4 minutes for head-to-toe acquisition. Low-dose non-contrast CT was performed for attenuation correction. PET image reconstruction parameters were 4i5s 440x440 matrix allpass.
* Measured value, based on phantom studies performed on a single system. Biograph Vision Quadra has ≤249 ps based on acceptance values. Data on file.
** Based on bench testing (e.g. improved sensitivity and ToF per NEMA NU-2:2018). Please refer to the approved PET drug prescribing information for dosing and administration instructions.
Findings
The MIP image of the 18F-FDG PET/CT study (Figures 1 and 2) shows total transposition of all organs reflecting situs inversus totalis. There was no well-defined focal hypermetabolism in the abdomen except reactive changes in the colonic surgical site at the hepatic flexure (Figure 3), which suggests no clinically significant metastatic lesions. The incidental finding of situs inversus totalis is a rare clinical condition which was defined on the PET/CT study.
Figure 1: Whole body 18F-FDG PET MIP and coronal fused PET/CT images show situs inversus totalis with the liver on the left and spleen and heart on the right with complete transposition of the aortic arch and colon. PET MIP image shows high image quality despite fast 4-minute head-to-toe acquisition. No focal hypermetabolic lesion visualized in the abdomen or pelvis. Mild hypermetabolism at the hepatic flexure at the site of previous surgery reflects reactive changes at the site of colonic surgery harbouring multiple surgical clips. Coronal fused images show chemotherapy catheter within the transposed right atria.
Discussion
Situs inversus totalis is a rare congenital anomaly which originates from an early disturbance of the left-right axis in the embryonic phase. Motile cilia normally generate a left-directed fluid flow within the embryo. If this flow is disrupted, visceral rotation and organ positioning are laid out in mirror image. This results in the situs inverses totalis in which the position of the thoracic and abdominal organs are opposite to normal and presents a mirror image with normal subjects.1 This condition affects 0.01% of the population.2 Most are asymptomatic, but the condition is associated with congenital cardiac defects and Kartagener syndrome (triad of chronic sinusitis, bronchiectasis and dextrocardia and situs inversus totalis).3
There are several case reports of incidental findings of situs inversus totalis in 18F-FDG PET/CT. Liu et al. (2022) published a case report of situs inversus totalis in a patient with left lung small cell neuroendocrine carcinoma.4 Identifying anatomical variations due to situs inversus totalis by PET/CT was key to proper staging and therapy planning for this tumor. Situs inversus totalis has been demonstrated with lung cancer with 18F-FDG PET/CT,5 with sigmoid carcinoma and incidental pheochromocytoma,6 and with cholangiocarcinoma.7 In the clinical example discussed above of situs inversus totalis with colon carcinoma in the hepatic flexure, 18F-FDG PET/CT shows complete tumor resection without any hypermetabolic metastatic lesion, while the clinical evaluation ruled out any other concomitant cardiac congenital anomaly or bronchiectasis.
The 18F-FDG PET/CT study performed on the Biograph Vision Quadra showed high image quality with sharp definition of vascular and colonic structures even with fast 4-minute head-to-toe and 3-minute head-to-mid-thigh revision acquisition times using the 106 cm LAFOV and 1-minute acquisition for the extremities. This reflects ultra-high sensitivity of the Biograph Vision Quadra and its ability to define very early lesions due to the excellent lesion contrast and high count rate capability.
Examination protocol
Fludeoxyglucose F 18
Please see Indications and Important Safety Information for Fludeoxyglucose F 18 (18F FDG) Injection.