Skeletal muscle metastasis from squamous cell lung cancer was first found by ultrasound: a case report.

Skeletal muscle metastasis (SMM) is rare and very difficult to diagnosis using routine ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI), especially in patients without a definitive tumor history. In this report, we describe a 64-year-old man who came to hospital because of pain from a touchable mass at his left thigh. Ultrasonography showed a substantive hypoechoic mass within the left adductor longus muscle with an anechoic area, which was ill-defined and rich in blood supply on color Doppler flow imaging (CDFI). The mass was biopsied under ultrasound guidance. The pathological findings displayed an infiltration of moderately differentiated squamous cell lung cancer (SCLC) and nests of atypical cells. Thoracic plain CT images displayed thickening of the bronchus wall of the right inferior lobe, with obstructive pneumonia and atelectasis at the distal bronchus. The final main diagnosis for this patient was central bronchogenic carcinoma, with intramuscular metastasis of the left adductor longus muscle, and the TNM classification was T2N0M1. Although the incidence of IM originating from SCLC is very rare, patients with an occasional found mass in soft tissue should be examined to exclude SMM, and ultrasound-guided percutaneous biopsy can provide vital information regarding indeterminate soft tissue masses.