Extranodal NHL comprises for 20–30% of all cases, and primary muscular lymphoma is an uncommon form that typically affects the lower limbs [7]. Only 8 lymphoma cases out of 7,000 (0.1%) were diagnosed as muscle lymphoma of the extremities, according to a 10-years study by Travis et al [8]. Diffuse big B-cell immunophenotype primary skeletal muscle NHL is extremely uncommon which was first reported by Kandel et al [9] in 1984 and is found in about 0.5% of extranodal lymphomas. Therefore, only a few cases of DLBCL developing largely from skeletal muscle, particularly the psoas major muscle, have been reported. It is a significant item to consider in the differential diagnosis of other cancers, despite its rarity.

Several research have reported on imaging modalities for the diagnosis of skeletal muscle lymphoma. Using CT, the tumors usually appear as low density or iso-density masses in the skeletal muscle [10]. Although nonspecific, US is useful and convenient for delineating soft tissue lesions. The sonographic, as an initial investigation tool of this lesion, showed an ill-defined hypoechoic mass with preservation of the underlying muscle architecture. Skeletal muscle lymphoma usually takes the form of irregular, poorly defined hypoechoic masses with a texture similar to muscular fibers that maintain continuity with adjacent muscles [11]. Other studies reported that the color Doppler US may show hypervascularity within the lymphoma which is similar to our report [5, 12].

Musculoskeletal soft tissue tumors are very common and diverse lesions, ranging from benign and malignant tumors to tumor-like lesions [13]. Vascular supply is an important identification point to differentiate benign from malignant tumors [14]. The non-hepatic CEUS, an emerging application, is concerned with the use of microbubble ultrasound contrast outside the liver which is a recognized imaging tool in the characterization of lesions to increase signal backscattering from the blood [15]. CEUS can detect both tumor angiogenesis and vascularity. Loizides et al [16] identified peripheral enhancement with a non-enhanced central area have a positive predictive value (PPV) of 86 percent and a negative predictive value (NPV) of 88 percent in discriminating benign from malignant tumors and the perfusion pattern is consistent with our results. Another study showed that the rapid arterial vascularization time (<11 s) was linked to a higher risk of malignancy [17] and the arterial perfusion in our case was just very rapid (10 s).

However, only a few earlier reports of CEUS used in skeletal muscle lymphoma have been reported, and the relationship between CEUS and pathological characteristics remains unclear. In a study about CEUS and intestinal lymphoma reported that high proportion of cases had arterial hyperechoic enhancement followed by venous wash out, as well as a high rate of central necrosis (61.1%) was observed which was more frequent in aggressive subtypes [18]. A study by Trenker et al [19] showed that renal lymphoma consistently showed washout in the late phase, and it can help to distinguish renal lymphoma from benign tumors. Therefore, the above studies confirmed that the extranodal lymphoma is a rich blood supply mass which grows rapidly, and it is prone to central necrosis. Thus, our results showed that skeletal muscle DLBCL displayed almost identical CEUS patterns.