(ChemotherapyAdvisor)–Computed tomography (CT) image features might be useful in differentiating thymus malignancies from benign lesions, possibly allowing fewer unnecessary invasive procedures, according to a retrospective study presented at the Radiological Society of North America (RSNA)’s 2012 Scientific Assembly and Annual Meeting in Chicago, IL.

“Absence of intralesional fat, a left or right of midline location, and a non-thymic shape were (independently) statistically associated with malignant thymic lesions,” reported lead author Aoife McErlean MBBCh, FFRRCSI, of the Radiology Department, Children’s University Hospital, in Dublin, Ireland, and coauthors. “Patients who are older, had infiltration of the mediastinal fat and increased lesion short axis dimension had greater odds of a malignant lesion.”

Increasing use of CT has lead to more frequent incidentally-identified asymptomatic thymic lesions in the anterior mediastinum, the authors noted. Detection of preclinical or benign ‘incidentalomas’ can lead to unnecessary invasive biopsies and interventions, so the authors studied if CT features are useful in distinguishing between benign thymic lesions and early-stage malignancies of the thymus.

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Preoperative CT images for 66 patients who had undergone thymectomy during 2007-2010 were reviewed by radiologists blinded to the patients’ pathology results. Image assessments followed International Thymic Malignancy Interest Group (ITMIG) definitions.

“There were 38 (58%) malignant and 28 (42%) benign thymic lesions in the study group,” the authors reported. “Malignant tumors were larger, with a median short axis dimension of 31.0mm compared to 19.5mm for benign lesions (P=0.028), and were more frequently located in the left or right of the anterior mediastinum as opposed to the midline (P =0.029). Intralesional fat was seen exclusively in benign thymic masses (P =0.002).”

Patients with thymic malignancies were significantly older (median age, 60.0 years) than those with benign-lesions (median age, 49.5 years; P=0.007), they reported.

“Seven benign (25%) but only 1 (2.6%) malignant tumors had a thymic (triangular) shape (P=0.023),” the authors noted. “In multivariate analysis, patient age, short axis dimension and infiltration of the mediastinal fat were significant independent predictors of malignant pathology.”

“Some CT features of thymic masses may be helpful in suggesting a benign etiology, therefore possibly avoiding unnecessary invasive procedures,” they concluded.