The acetabular fossa hot spot on ¹⁸ F-FDG PET/CT: epidemiology, natural history, and proposed etiology

Abstract

Objective

To describe a benign focus of increased activity in the acetabular fossa (the acetabular fossa hot spot, AFHS) on ¹⁸ F-FDG PET/CT that can mimic a neoplasm.

Materials and methods

¹⁸F-FDG PET/CT images from four patient populations were examined. Group 1 (n = 13) was collected from a search of radiology reports and used to define the AFHS and for hypothesis generation. Group 2 (n = 1,150) was used for prevalence of AFHS. Group 3 (n = 1,213) had PET/CT and MRI pelvis within a week of each other and was used to correlate metabolic and anatomic findings. Group 4 (n = 100) was used to generate the control group. Data were collected on demographics, common comorbidities, underlying cancer diagnosis and status, and hip symptoms.

Results

Prevalence of AFHS was 0.36 % (95 % CI 0.10–0.91 %). None progressed to malignancy or was associated with cancer status. The majority (71 %) were on the left, and 6 % were bilateral. Mean SUV_max of the AFHS was 4.8 (range, 2.7–7.8). Male patients were more likely to have the AFHS (OR = 8.69, 95 % CI 1.88–40.13). There was no difference with respect to other collected data, including hip symptoms. Average minimum duration of AFHS was 346 days (range, 50–1,010 days). Readers did not detect corresponding hip abnormalities on MRIs.

Conclusions

AFHS is a benign finding that may be caused by subclinical ligamentum teres injury, focal synovitis, or degeneration of acetabular fossa fat. Despite uncertainty regarding its etiology, recognition of AFHS as a benign finding can prevent morbidity associated with unnecessary biopsy or initiation of therapy.