Psoas muscle metastasis from cervical carcinoma: Correlation and comparison of diagnostic features on FDG-PET/CT and diffusion-weighted MRI.

Psoas muscle metastasis, though rare, is the commonest site of skeletal muscle involvement in cervical carcinoma. The appropriate clinical management of this condition, particularly of the pain related to malignant psoas syndrome, is still evolving and the diagnostic features on conventional morphological imaging modalities are often non specific, with the differential diagnosis lying between sarcoma, hematoma, and abscess. In this report, a comparison of various morphofunctional imaging modalities was made. Fluorodeoxyglucose-positron emission tomography (FDG-PET)/computed tomography (CT) was the first to suspect disease involvement of the psoas muscle, demonstrating intense FDG uptake (compared with the contralateral muscle), while ultrasound showed heterogeneous echotexture, and magnetic resonance imaging (MRI) showed subtle altered signal intensity in the right psoas muscle. Both anatomical imaging modalities and non contrast CT of the PET-CT examination demonstrated a bulky psoas muscle, without any focal abnormality. On diffusion-weighted imaging of MRI (DWI-MRI), restricted diffusion of the involved muscle was an important observation. The psoas muscle metastatic involvement was proven histopathologically. Thus, enhanced glucose metabolism and restricted diffusion in the newer non-invasive molecular imaging modalities (e.g., PET/CT and DWI-MRI) could serve as valuable adjunctive parameters in diagnosing this entity in the absence of a focal abnormality in the anatomical modalities. In the treatment response monitoring scenario, FDG-PET/CT demonstrated near complete resolution following administration of 3 cycles of systemic chemotherapy and local external radiotherapy.