A 56-year-old male presented with left thigh progressive pain. A firm mass was palpated at the posteromedial side of the thigh. Patient's medical history included surgery for colon cancer seven months ago. The patient was referred for thigh ultrasound (US), given the localization and palpable nature of the finding.
Using a linear high-frequency transducer (10 MHz), the ultrasonographic examination revealed a well-defined, solid, iso- to hypo-echoic mass, measuring 4 x 5 x 4.5 cm. It was located inside the biceps femoris muscle manifesting mass effect to the adjacent tissues (Fig. 1a). The mass demonstrated a stalk on its posterior aspect and increased peripheral and central vascularity on colour and power Doppler examinations (Figs 1b, 1c). Furthermore, spectral Doppler showed an arterial waveform with increased velocities (Fig. 1d). After surgical removal, the histopathological examination confirmed the diagnosis of intramuscular metastasis from colon adenocarcinoma (Fig. 2). The patient had an uneventful recovery from surgery, being under surveillance with no signs of recurrence.
Skeletal muscle metastases (SMM) are uncommon, although skeletal muscles account for approximately 40% of total body weight. The prevalence of SMM varies, with some authors reporting rates from 0.03 to 17.5%, based on post-mortem autopsies of patients with cancer [1–3]. Most common types of primary tumours metastasizing to skeletal muscles are adenocarcinomas of the lung, the gastrointestinal tract and urogenital malignancies. Thigh muscles, iliopsoas, gluteal and paravertebral muscles are the most often affected muscles [1,4–6]. SMM may be asymptomatic, constituting incidental findings, or it may manifest as a palpable mass with local pain, tenderness, swelling and/or erythema; the patient may complain for reduced range of motion of the affected area, or for systematic symptoms such as fever, weight loss, malaise and anorexia [1,3,7]. Clinical examination may reveal a skeletal muscle lump on palpation. However, imaging with US, CT and MRI plays an important role in the diagnostic approach and further evaluation of these lesions. MRI is considered, by some authors, superior to other imaging modalities in detecting intramuscular metastases. The definite diagnosis, however, will be made by the histopathological analysis, preferably after a US or CT guided biopsy, or after lesion’s surgical excision [3,7]. Indeterminate lesions, or lesions in which therapy is dependent on histology results, should be biopsied [8]. After the diagnosis is made, a multidisciplinary meeting should be held in order all involved specialists (e.g., surgeon, radiologist, histopathologist) to discuss for the next best step. Regarding US, a percentage of SMM appear hypoechoic [2,5,6,9], as in our patient; however, hyperechoic appearance has also been reported [10]. In our case, the stalk-like structure of the lesion with its central feeding artery emerging from the deep femoral artery indicated neoangiogenesis, consistent with malignancy. The aforementioned US findings, i.e., stalk, feeding artery and multi-branching hypervascularity have not been previously reported in SMM from colon cancer, to the best of our knowledge. Due to the US imaging appearance combined with past medical history, the patient was referred to surgery without any further workup. After surgical removal, the histopathological examination confirmed the diagnosis of intramuscular metastasis from colon adenocarcinoma.
Take Home Message / Teaching Points
US is considered the appropriate initial triage imaging modality for the evaluation of intramuscular soft tissue lesions.
The US imaging findings including iso to hypo-echogenicity, hypervascularity with a multi-branching configuration, high-resistance arterial pattern and a stalk with a feeding artery, are features that suggest malignancy.
US findings are able to rapidly and correctly direct clinicians to the diagnosis and appropriate treatment of SMM.
Written informed patient consent for publication has been obtained.
Skeletal muscle metastasis
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
According to the ultrasound images, a relatively distinct hypoechoic lesion is visible within the posterior medial muscle layer of the left thigh, with heterogeneous internal echoes. Under the color Doppler mode, significant blood flow signals are observed, showing multi-branch, high-flow, and high-resistance arterial supply characteristics. A “pedicle-like” structure is also noted, where the feeding artery originating from the deep femoral artery enters directly into the center of the lesion. The boundaries of the surrounding muscle structure are slightly affected, but the overall muscle layer is still discernible.
Considering the patient’s age (56 years), previous surgical history of colon cancer, imaging characteristics (hypoechoic lesion, high-resistance arterial flow, and a pedicle-like feeding structure), and confirmation by postoperative pathology, the most likely diagnosis is: Intramuscular Metastasis from Colon Adenocarcinoma.
For patients diagnosed with intramuscular metastasis from colon adenocarcinoma, the following treatments are typically considered:
After surgery and other tumor treatments, patients may experience local pain, tissue damage, and systemic fatigue. Rehabilitation training should be progressive and individualized:
Throughout the rehabilitation process, pay close attention to:
The above report is based on an analysis of existing data and is provided for clinical reference only. It does not replace an in-person consultation or professional medical advice. Patients should undergo further examination or treatment under the guidance of a specialist and complete rehabilitation exercises in the presence of qualified personnel.
Skeletal muscle metastasis
