New sclerotic lesions on CT may represent treatment response, not progression of metastatic disease
A 54-year-old man with squamous cell carcinoma of the lung with lymph node and osseous metastases underwent treatment with systemic chemotherapy.
After remission for 4 years, he developed abdominal discomfort, nausea and vomiting. PET/CT revealed a locally invasive central right upper lobe lung mass with peripheral extension along the bronchovascular bundle; confluent right hilar, right supraclavicular and right cervical metastases; and multiple osseous metastases.
New sclerotic lesions
Follow-up PET/CT revealed interval decrease in size and metabolic activity of the right cervical and supraclavicular lymph nodes compatible with partial treatment response (Figure 1).
Similar partial anatomic and metabolic response was noted in the mediastinal and right hilar lymph node mass (Figure 3), with subsequent improvement of the obstructive changes in the right upper lobe (Figure 4). The right upper lobe mass also showed partial metabolic and anatomic improvement (Figure 5).
There was overall positive metabolic treatment response seen in the multiple fluorine-18 fluorodeoxyglucose (FDG) avid osseous metastases, including in the bilateral ribs, thoracolumbar spine, sternum and pelvic bones (Figure 6).
There was interval development of new sclerotic lesions and/or progression of preexisting sclerotic lesions at the sites of decreasing metabolic activity, such as in the right iliac wing (Figures 7 and 8), left iliac bone (Figure 9) and lateral half of the T3 vertebral body (Figure 10).
Based on the clinical and biochemical evidence of marked positive treatment response, it appeared unlikely that these apparently new/progressing sclerotic lesions represented progression of metastatic disease. Rather, they seemed to represent healing/remodeling changes of treatment response.
Squamous cell carcinoma of the lung comprises about 10% to 15% of lung cancers. This type of lung cancer is the most aggressive and rapidly growing of all types.
Squamous cell carcinoma of the lung is strongly related to cigarette smoking, with only a small fraction of these tumors occurring in nonsmokers.
After chemotherapy, PET/CT documented a mixed pattern of improvement and progression osseous lesions, which included improvement of the metabolic activity of the FDG-avid sclerotic metastases.
This case demonstrates a good example of the paradoxical CT demonstration of new/progressive sclerotic osseous metastatic lesions when, in fact, the overall disease is improving metabolically and anatomically.
This phenomenon can occur when the metastatic lesions are initially isodense to the surrounding skeleton and not detectable on the initial CT examination.
When the metastatic disease responds to chemotherapy, resultant osteoblastic reaction makes the lesions appear more sclerotic compared with the background density of the bones, thus becoming evident on the follow-up CT scan but mimicking development of new metastatic lesions.
Availability of PET images improves accuracy of assessment, identifies the osseous metastases before actual morphologic appearance of the metastatic lesions on the initial examination, and appropriately categorizes them on follow-up images as responding to therapy.
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Munir Ghesani, MD, FACNM, is assistant professor of radiology and director of PET/CT fellowship at NYU Langone Medical Center in New York. He also serves as a HemOnc Today Editorial Board member. He can be reached at email@example.com.
Ajit Karakbelkar, MD, is a PET/CT fellow at NYU Langone Medical Center.
Disclosure: Ghesani and Karakbelkar report no relevant financial disclosures.