Distinguishing Benign Thymic Lesions from Early-Stage Thymic Malignancies on Computed Tomography

Abstract

Introduction The increasing use of computed tomography (CT) has led to more-frequent identification of asymptomatic lesions in the anterior mediastinum. The purpose of this study is to identify CT features that distinguish benign thymic lesions from early stage malignant thymic neoplasms. Methods We retrospectively reviewed preoperative CT imaging for 66 patients who had undergone thymectomy for benign thymic lesions or early stage malignant thymic neoplasms. All variables with a p-value <0.2 on univariate logistic regression analysis were evaluated by multivariate analysis. Stepwise selection was performed, and variables with a p-value <0.05 were retained in the final model. Results Thirty-eight malignant (58%) and 28 benign thymic lesions (42%) were included. Patients with benign thymic tumors were significantly younger (median age, 49.5 years) than patients with malignant tumors (60.0 years; p=0.007). Malignant tumors were larger in short-axis dimension (p=0.028) and more frequently in a non-midline location in the anterior mediastinum (p=0.029). Intralesional fat was seen exclusively in benign masses (p=0.002). Seven benign tumors (25%) and 1 malignant tumor (2.6%) had a triangular thymic shape (p=0.023). In multivariate analysis, lower age, smaller short-axis dimension, and lack of infiltration of the mediastinal fat were significant independent predictors of benign pathologic results. Conclusion Intralesional fat, midline location, and triangular thymic shape are more frequently found in benign thymic lesions. Lack of infiltration of the mediastinal fat, younger patient age, and smaller size are independent predictors of benign thymic lesions. These features may help characterize thymic masses as benign and avert potentially unnecessary invasive diagnostic procedures.

Intrathymic cyst: Clinical and radiological features in surgically resected cases

“…In terms of the demographics of patients with histopathologically proven intrathymic cysts, the median age was 56 years with a range of 37–79 years, which is similar to the previously reported age range of patients with thymic tumours including thymic epithelial tumours, thymic carcinoid, and lymphoma 4, 5, 20-22 . In a recent study by McErlean et al ., 5 it was suggested that indeterminate thymic lesions in patients <43 years tend more often to be benign.…”

“…Pathology reports were reviewed by a board-certified anatomic pathologist (L.S.) to determine the pathological subcategories of intrathymic cysts, such as thymic cysts and bronchogenic cysts 5, 19 . Thymic cysts were also subcategorized into multilocular or unilocular according to the histopathology reports.…”

“…Although multiple studies have evaluated the radiological manifestations of thymic neoplasms, such as thymomas and thymic carcinoma 4,5 , there are few studies focused on the radiological manifestations of benign entities of the thymus, such as cysts or hyperplasia 6–8 . In particular, the imaging characteristics of intrathymic cysts have rarely been studied, except for being mentioned in comparison to thymic neoplasm, under the non-specific category of “benign thymic pathology” 5 .…”

“…Acquired thymic cysts are reported to be associated with radiation therapy for Hodgkin’s disease 13, 14 , thymic tumour 15 , thymic hyperplasia 16 , thoracostomy or chest trauma, 17 and human immunodeficiency virus (HIV) infection 18 . Although less common than thymic neoplasms, thymic cysts are one of the most common benign thymic lesions 5 . One of the challenges to the systematic radiological investigation of the entity is the lack of surgical and pathological confirmation for asymptomatic patients with imaging features strongly suggestive of simple cysts without suspicion for solid neoplasm.…”

Imaging Characteristics of Pathologically Proven Thymic Hyperplasia: Identifying Features That Can Differentiate True From Lymphoid Hyperplasia

“…However, a variety of pathologic conditions can involve the gland, which then presents challenges to radiologists who aim to provide accurate diagnosis and aid patient management [3, 4]. Imaging characteristics of neoplastic processes of the thymus, especially thymic epithelial tumors, have been well studied and reported in cohorts of patients with pathologically proven disease [2, 5–11]. However, the imaging features of nonneoplastic conditions such as thymic hyperplasia have not been systematically studied in a cohort of patients with pathologically confirmed diagnoses.…”