Case of the Month - August 2017

This case can be downloaded and read as an PDF or read on this page below.

Click here to view the PET and CT images for this case through an interactive website provided by Hermes Medical Solutions.

Clinical History

75-year-old male ex-smoker with a left upper lobe nodule. PET-CT requested to further characterise.

Findings

An FDG scan was acquired from skull base to below knees together with a low dose CT scan for attenuation correction and image fusion.

There is a 1.2 cm part-solid nodule within the left upper lobe, axial CT image 272, which shows only low-grade uptake, SUV max 1.5. There is no abnormal hilar or mediastinal nodal uptake.

There is a very avid uptake associated with a predominantly fat density right latissimus dorsi intramuscular lesion measuring 8x5x9 cm, SUV max 11.6. The lesion appears to extend posterior to the shoulder girdle with a further separate site of avid uptake within the subcutaneous tissues overlying the right scapula, see axial fused image 276. Uptake related to bilateral shoulder girdle musculature appears physiological.

FDG uptake is otherwise within normal physiological limits.

Interpretation

Uptake within the left upper lobe nodule is low-grade and it may be benign or represent low-grade malignancy. Continued CT surveillance suggested.

The FDG avid right shoulder girdle lesion needs further assessment with MRI. The scan findings maybe in keeping with a benign hibernoma but it would be prudent to exclude a malignant tumour such as a liposarcoma.

Follow-up

The patient subsequently underwent a dedicated MRI of the right shoulder, which demonstrated a well-defined lesion deep to the right latissimus dorsi muscle with predominantly fat signal, with thin internal septa, vessels, and a small amount of oedema. The patient was subsequently reviewed at a dedicated sarcoma centre, and a diagnosis of a hibernoma was made based on the combination of clinical findings and multimodality imaging appearances.

Key Teaching points and Discussion

References

Smith CS, Teruya-Feldstein J, Caravelli JF, Yeung HW. False-positive findings on 18F-FDG PET/CT: Differentiation of Hibernoma and Malignant Fatty Tumour on the Basis of Fluctuating Standardized Uptake Values. AJR 2008; 190:1091-1096

Kim JD, Lee HW. Hibernoma: Intense Uptake on F18-FDG PET/CT. Nucl Med Mol Imaging 2012; 3: 218-222

Murphey MD, Carroll JF et al. From the archives of the AFIP: benign musculoskeletal lipomatous lesions. Radiographics. 2004; 5: 1433-66.