E1311. Chordoma: 18F-FDG PET/CT and MRI Imaging Features
  1. Joshua Olson; Mayo Clinic
  2. Doris Wenger; Mayo Clinic
  3. Peter Rose; Mayo Clinic
  4. Ivy Petersen; Mayo Clinic
  5. Stephen Broski; Mayo Clinic
To examine the 18F-fluorodeoxyglucose (18F-FDG) PET/CT and MRI imaging characteristics of chordoma.

Materials and Methods:
All institutional cases of biopsy-proven chordoma with a pre-therapy 18F-FDG PET/CT from 2001 through 2019 in patients >18 years old were retrospectively reviewed. Multiple PET/CT and MRI imaging parameters were assessed.

23 chordoma patients were included (16M, 7F; average age of 60.1 ± 13.0 years), including 13 sacrococcygeal, 9 mobile spine, and one clival lesions. Comparative MRI imaging was available in 22/23 cases. The average largest dimension was 7.5 ± 3.6 cm (range 2.8 – 19.8 cm), and average volume was 385.3 ± 714.4 cm3 (range 12.2 - 3423.2 cm3). On 18F-FDG PET/CT, chordomas had an average maximum standardized uptake volume (SUVmax) of 5.8 ± 3.7 (range 2.3 – 20.0), average metabolic tumor volume (MTV) of 160.2 ± 263.8 cm3 (range 11.1 – 1226.0 cm3), and average total lesion glycolysis (TLG) of 542.6 ± 1210.1 g (range 28.9 – 5972.1 g). All chordomas demonstrated heterogeneous FDG activity. No patients had metastatic disease on staging 18F-FDG PET/CT. Most chordomas contained mineralization/sequestered bone [14/23 (61%)], were lytic or mixed lytic/sclerotic [22/23 (96%)], had an associated soft tissue mass [23/23 (100%)], involved more than one vertebral level [19/22 (86%)], and extended into the posterior elements [21/22 (95%)]. On MRI, chordomas were predominantly T2 hyperintense [22/22 (100%)], T1 isointense [18/22 (81%)], contained small foci of T1 hyperintensity [17/22 (77%)], and demonstrated heterogeneous enhancement [14/20 (70%)]. There were no statistically significant associations found between 18F-FDG PET/CT and MRI imaging features. 22/23 (96%) patients had imaging follow-up over a mean duration of 3.6 ± 2.5 years and 6/22 (27%) patients developed local recurrence or metastatic disease. There was no relationship of SUVmax (p = 0.53), MTV (p = 0.47), TLG (p = 0.48), maximal dimension (p = 0.92), or volume (p=0.45) to the development of recurrent or metastatic disease.

On 18F-FDG PET/CT imaging, chordomas demonstrate moderate, heterogeneous FDG uptake. They typically contain mineral or sequestered bone, involve more than one vertebral level, extend into the posterior elements, and are lytic or mixed lytic/sclerotic. Predominant T2 hyperintensity and small foci of internal increased T1 signal are common on MRI. The inherent FDG avidity of chordomas suggests that 18F-FDG PET/CT may be a useful modality for staging, evaluating treatment response, and assessing for recurrent or metastatic disease.