What Is the Clinical Importance of Incidental Findings on Staging CT Scans in Patients With Sarcoma?
Authors: Mayo Zachary , Kennedy Sean , Gao Yubo , Miller Benjamin J. 
Published: June 2018

Abstract

Background
Baseline staging CT scans are performed on nearly every patient after the diagnosis of a sarcoma to evaluate for the presence of metastatic disease. These scans often identify abnormalities that may or may not be related to the known malignancy. Despite the high frequency of incidental findings, there is little guidance for clinicians faced with assessing these radiographic abnormalities. The interpretation of incidental findings is important because it may influence decisions regarding surveillance frequency, prognostic estimation, and surgical and medical intervention.

Questions/purposes
The purpose of this study was to determine (1) the frequency of abnormal findings and indeterminate nodules on staging CT scans; (2) the natural history of indeterminate nodules identified at the time of sarcoma diagnosis; and (3) the factors associated with indeterminate nodules representing true metastatic disease.

Methods
Between September 2010 and February 2016 we treated 233 patients with bone and soft tissue sarcomas. Of those, 227 (97%) had a staging CT scan of the chest or chest/abdomen/pelvis performed within 2 months of diagnosis. To be eligible for this retrospective study, a patient had to have a minimum of 6 months of radiographic followup after that initial CT scan. A total of 36 (16%) were lost to followup or did not have radiographic surveillance at least 6 months later, and 48 (21%) were excluded for other prespecified reasons, leaving 149 patients for evaluation. We recorded all abnormal findings listed in the official radiology CT report of the lung, bone, liver, and lymph nodes. We assessed progression of indeterminate nodules by reviewing radiology reports, which listed both size and number of findings, and clinical notes outlining the current assessment of disease status and treatment plan. If indeterminate nodules grew in size or number consistent with metastatic disease or were confirmed histologically, they were considered to represent true metastasis. Bivariate methods were used to investigate an association between various clinical factors, which were obtained from chart review, and progression of indeterminate nodules to clear metastatic disease.

Results
One hundred thirty-five of 149 patients (91%) had at least one abnormal finding on a staging CT scan. Forty-nine patients (33%) presented with indeterminate lung nodules, 15 (10%) with indeterminate liver lesions, four (3%) with indeterminate bone lesions, and 57 (38%) with enlarged lymph nodes. Fifteen of the 49 patients with indeterminate lung nodules (31%), one of 15 liver nodules, zero of four bone lesions, four of 13 lymph nodes 1 to 2 cm in size, and two of 44 subcentimeter lymph nodes (4.5%) were clearly metastatic on followup. A primary tumor size ≥ 14 cm in greatest dimension was more suggestive of indeterminate nodules representing true metastatic disease compared with smaller primary tumors in both lung (eight of 10 compared with seven of 36 [19%]; odds ratio, 16.6; 95% confidence interval, 2.9-95.9; p < 0.001) and lymph nodes (six of 18 compared with zero of 36 [0%], p < 0.001).

Conclusions
It is extremely common for abnormal findings and incidental nodules to be present at the time of a staging CT scan in patients with sarcoma. Although patients with indeterminate nodules should have continued surveillance, it appears from this study that the majority of these findings do not represent true metastatic disease. Given a minimum followup of 6 months, it is possible the actual proportion of indeterminate lesions representing true metastatic disease may increase over time.

Level of Evidence
Level III, prognostic study.