Multiple and solitary skeletal muscle metastases on 18F-FDG PET/CT imaging

Striated muscle: an inadequate soil for cancers

Many organs of the body are susceptible to cancer development. However, striated muscles-which include skeletal and cardiac muscles-are rarely the sites of primary cancers. Most deaths from cancer arise due to complications associated with the development of secondary metastatic tumours, for which there are few effective therapies. However, as with primary cancers, the establishment of metastatic tumours in striated muscle accounts for a disproportionately small fraction of secondary tumours, relative to the proportion of body composition. Examining why primary and metastatic cancers are comparatively rare in striated muscle presents an opportunity to better understand mechanisms that can influence cancer cell biology. To gain insights into the incidence and distribution of muscle metastases, this review presents a definitive summary of the 210 case studies of metastasis in muscle published since 2010. To examine why metastases rarely form in muscles, this review considers the mechanisms currently proposed to render muscle an inhospitable environment for cancers. The "seed and soil" hypothesis proposes that tissues' differences in susceptibility to metastatic colonization are due to differing host microenvironments that promote or suppress metastatic growth to varying degrees. As such, the "soil" within muscle may not be conducive to cancer growth. Gaining a greater understanding of the mechanisms that underpin the resistance of muscles to cancer may provide new insights into mechanisms of tumour growth and progression, and offer opportunities to leverage insights into the development of interventions with the potential to inhibit metastasis in susceptible tissues.

Mechanisms Underlying the Rarity of Skeletal Muscle Cancers

Skeletal muscle (SKM), despite comprising ~40% of body mass, rarely manifests cancer. This review explores the mechanisms that help to explain this rarity, including unique SKM architecture and function, which prohibits the development of new cancer as well as negates potential metastasis to SKM. SKM also presents a unique immune environment that may magnify the anti-tumorigenic effect. Moreover, the SKM microenvironment manifests characteristics such as decreased extracellular matrix stiffness and altered lactic acid, pH, and oxygen levels that may interfere with tumor development. SKM also secretes anti-tumorigenic myokines and other molecules. Collectively, these mechanisms help account for the rarity of SKM cancer.

Skeletal muscle metastasis from colorectal adenocarcinoma: A literature review

BACKGROUND

Colorectal adenocarcinoma is the third most common cancer worldwide. It accounts for almost 10% of all cancer-related deaths. Skeletal muscle is a very unusual site for metastasis from colorectal cancers and is associated with a poor prognosis and high mortality.

AIM

To review the literature for cases of skeletal muscle metastasis (SMM) from colorectal adenocarcinoma.

METHODS

A systematic literature search using a validated search strategy was carried out to identify the incidence of SMM associated with colorectal adenocarcinoma. The studies identified were tabulated in a PRISMA, and data was extracted in a tabulated form.

RESULTS

Twenty-nine studies were included in this literature review. SMM was most commonly detected in the thigh muscles. Most of the tumours had originated from the rectum or the right colon. The histopathology of the primary tumour was generally advanced. The mean time interval between the primary tumour and onset of SMM was 22 mo. In 3 cases, asymptomatic SMM had been picked up by advanced imaging systems, like fluorodeoxyglucose-positron emission tomography scan.

CONCLUSION

SMM from colorectal adenocarcinomas is a rare complication. However, it is possible that the low incidence could be due to under-reporting. Early use of advanced imaging techniques and a high index of clinical suspicion might increase the reporting of SMM from colorectal adenocarcinoma.

Skeletal muscle metastasis with bone metaplasia from colon cancer: A case report and review of the literature

BACKGROUND

Colon cancer is a common malignant disease of the gastrointestinal tract and usually occurs at the junction of the rectum and sigmoid colon. Lymphatic and hematogenous metastases occur frequently in colon cancer and the most common metastatic sites include the liver, lung, peritoneum, bone, and lymph nodes. As a manifestation of advanced tumor spread and metastasis, soft tissue metastasis, especially skeletal muscle metastasis with bone metaplasia caused by colon cancer, is rare, accounting for less than 1% of metastases.

CASE SUMMARY

A 43-year-old male patient developed skeletal muscle metastasis with bone metaplasia of the right proximal thigh 5 mo after colon cancer was diagnosed. The patient was admitted to the hospital because of pain caused by a local mass on his right thigh. Positron emission tomography-computed tomography showed many enlarged lymph nodes around the abdominal aorta but no signs of lung or liver metastases. Color ultrasound revealed a mass located in the skeletal muscle and the results of histological biopsy revealed a poorly differentiated adenocarcinoma suspected to be distant metastases from colon cancer. Immunohistochemistry showed small woven bone components that were considered to be ossified.

CONCLUSION

This case reminds us that for patients with advanced colorectal tumors, we should be alert to the possibility of unconventional metastasis.

Practical Considerations When Interpreting FDG PET/CT Imaging for Staging and Treatment Response Assessment in Melanoma Patients

While FDG PET/CT bears a high sensitivity and specificity for the staging of stage III and IV melanoma as well as for the purpose of melanoma recurrence detection, overall results tend to vary from one part of the body to another as well as for melanoma from cutaneous or choroidal origin. In this paper, organ or site-related differences in sensitivity and specificity in melanoma patients, both from cutaneous and choroidal origin, as well as their impact on clinical decision making are discussed. Furthermore, with the advent of immunotherapy for the treatment of malignant melanoma, post-treatment related potential false positive findings have emerged, the knowledge of which is essential for accurate treatment response assessment. These post-treatment related potential false positive findings are summarized in this paper so as to help the nuclear medicine physician in avoiding erroneous interpretation of acquired FDG PET/CT images in melanoma patients receiving immuntherapy.

Skeletal muscle metastases of hepatocellular carcinoma: A case report and literature review

BACKGROUND

The metastasis of liver cancer to skeletal muscle is extremely rare compared to other sites. We herein report a case of rapidly developing skeletal metastases following liver transplantation due to primary liver cancer.

CASE SUMMARY

A 70-year-old male with underlying chronic hepatitis B virus infection was diagnosed with hepatocellular carcinoma (HCC), for which he underwent liver transplantation in 2014. Six years after receiving the transplant, pathological examination confirmed the presence of HCC without vascular invasion. He was admitted to the hospital with a rapidly growing mass on his right thigh. Ultrasound examination revealed a mixed echo mass in the lateral soft tissue of the middle part of the right femur. Magnetic resonance imaging showed heterogeneous iso-signal intensity on T1-weighted images and heterogeneous hyper-intensity on T2-weighted images compared to the surrounding muscles. Pathological examination of the ultrasound-guided needle biopsy specimen revealed that it was similar to the previously detected liver cancer; the diagnosis was metastasis of HCC. Surgical excision was performed. There were no other sites of metastasis, and the patient recovered well after surgery.

CONCLUSION

This report presents a rare case of skeletal metastasis following liver transplantation for HCC. The study suggests a possible role for skeletal muscle metastasis mechanisms, which should be the focus of future research.

The Path of Most Resistance: A Rare Instance of Metastatic Pancreatic Adenocarcinoma Identified Within Skeletal Muscle

Soft tissue neoplastic metastases, specifically to the skeletal muscle, are uncommon in comparison to metastases within the abdomen, thorax, or intracranial regions. Specifically, pancreatic adenocarcinoma with skeletal muscle metastasis is a rare clinical phenomenon and is hardly reported. There is a high mortality rate after the diagnosis of metastatic pancreatic adenocarcinoma, attributed to inadequate screening and advanced staging upon incidental discovery. Rarely, metastatic lesions manifest in the skeletal muscle and are hardly documented. Some of the factors that deter skeletal muscle tumor implantation include the deficiency of skeletal muscle mediators and genetic makeup of the primary tumor. Surgical resection of pancreatic adenocarcinoma with adjuvant chemotherapy demonstrates the best prognosis; however, surgical management is usually limited to patients without known metastatic disease. Alternative treatment options such as chemotherapy and radiotherapy are used in the palliative care setting. Here, we present the case of a patient with previously diagnosed and treated pancreatic adenocarcinoma in remission, with biopsy-proven metastases isolated within the skeletal muscle.

Imaging features and prognostic value of 18F-FDG PET/CT detection of soft-tissue metastasis from lung cancer: a retrospective study

BACKGROUND

Soft-tissue metastasis (STM) is a relatively rare, but not exceptional, manifestation of lung cancer. The purpose of this study was to evaluate the imaging features of STM from lung cancer using fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT), and assess the impact of STM detected at baseline PET/CT on patient survival.

METHODS

Out of 4543 patients with lung cancer who underwent ¹⁸F-FDG PET/CT in our hospital between January 2013 and September 2018, 85 were diagnosed with STM (78 at baseline PET/CT and 7 at restaging PET/CT) and included in the imaging study. We conducted a comparative survival analysis between patients with stage 4 lung cancer with and without STM at baseline PET/CT (n = 78 in each group) and performed univariate and multivariate analyses to investigate the factors affecting the prognosis of lung cancer.

RESULTS

A total of 219 lesions were identified by ¹⁸F-FDG PET/CT: 215 were detected by PET and 139 by CT. Muscle STM were primarily found in the hip and upper limb muscle, whereas subcutaneous STM were mainly distributed in the chest, abdomen, and back. In 68 patients, STM were found incidentally during routine ¹⁸F-FDG PET/CT staging. Isolated STM were detected in 6 patients, whose tumor staging and treatment were affected by PET/CT findings. There were no significant differences in the 1-, 3-, and 5-year survival rates between patients with and without STM at baseline PET/CT. Brain and adrenal metastases, but not STM, were associated with poor prognosis of stage 4 lung cancer.

CONCLUSIONS

We described the PET/CT imaging characteristics of STM from lung cancer, and confirmed that PET/CT can detect unsuspected STM to change the staging and treatment of some patients. Our analysis indicates that STM is not a useful prognostic indicator for patients with advanced lung cancer, while brain and adrenal metastases portend a poor prognosis.

The role of radiological and hybrid imaging for muscle metastases: a systematic review

AIM OF THE STUDY

Skeletal muscle metastases (SMM) are a rare entity, mainly detected at autopsy. Nevertheless, radiological and nuclear medicine imaging can contribute to the diagnosis with a significant impact on the treatment and prognosis of neoplastic patients. This study aimed to systematically review the features of SMM at imaging considering the primary tumors and the sites of occurrence.

MATERIALS AND METHODS

We conducted a systematic search of three electronic database (i.e., PubMed, Science Direct, and Web of Science) up to May 2019, without any language or time interval restriction. Two reviewers performed the search and selection process, data extraction, and synthesis. We resolved disagreements by consensus and/or involving a third reviewer. The included studies have been classified according to the Oxford Centre for Evidence Based Medicine (CEBM) grading system.

RESULTS

Out of 8598 and 1077 articles respectively for radiological and hybrid imaging, 29 papers were included. According to CEBM, twelve were level 4. Computed tomography (CT) is mainly applied and, despite the existence of CT and magnetic resonance-based classifications, these are rarely used. Positron emission tomography/CT allowed the detection of small and subtle lesion also in the extremities. Muscles of the trunk were mostly affected and mainly respiratory tumors are associated with this type of metastatic spread.

CONCLUSION

Radiological and hybrid imaging allow a precise characterization of SMM. However, a more systematic approach, including also the application of available classification systems, may increase the diagnostic accuracy for this rare type of metastases.

KEY POINTS

• Skeletal muscle metastases have heterogeneous characteristics at imaging but mostly abscess-like features and high metabolic activity are described. • Skeletal muscle metastases mainly affect the muscles of the trunk. • Pulmonary, urological, and gastrointestinal cancers are the most frequent cause of skeletal muscle metastases.

Skeletal muscle and solitary bone metastases from malignant melanoma: multimodality imaging and oncological outcome

Malignant melanoma solitary metastases to bone or skeletal muscle occur in 0.8% of patients. The aim of this study was to evaluate features of skeleton and muscle metastases with multimodality imaging and review the oncological outcome. Thirteen patients with melanoma metastases from January 2006 to February 2016 were included. Histologic confirmation was obtained. Imaging studies included computed tomography (CT), MRI, and/or positron emission tomography/CT. Treatment received and BRAF status were recorded. Differences in BRAF status and overall survival (OS) were analyzed using the χ²-test. Associations between OS and metastases were analyzed using Cox proportional models. Nine (69%) patients showed osseous involvement. Lower extremity bones were affected in three (23%) patients: first toe, right calcaneal spurs, and knee. The spine was involved in three (23%) patients. In two (15%) patients, the pelvic bones were involved. In one (8%) patient, the temporal bone was affected. Nine (70%) patients had a history of malignant melanoma, with a median time to progression of 28 months. The median OS was 18 months: 24 months in patients with a history of melanoma and 3 months in patients with metastases at first diagnosis. The median follow-up duration was 28 months. BRAF mutant versus wild-type tumors showed significant differences in OS (P=0.03). The hazard ratio for death in the metastatic group at diagnosis was 6.83, 95% confidence interval: 1.060–144.072 (P=0.04). Solitary metastases from melanoma to the skeleton and muscle are rare. CT, MRI, and positron emission tomography/CT are useful for the evaluation of musculoskeletal findings. Image findings are not definitive for diagnosing a malignant solitary lesion; thus, a pathologic confirmation with a biopsy is recommended.

Rectal adenocarcinoma presenting with thigh muscle metastasis as the only metastatic site

Rectal carcinoma with metastasis to skeletal muscle is a rare finding. According to literature review, 17 cases of skeletal muscle metastasis from colorectal carcinoma have been documented where only six cases were rectal carcinomas.We discuss a case of a middle-aged man with a known history of high-grade mucinous adenocarcinoma of the rectum, status post abdominoperineal resection followed by adjuvant radiotherapy and chemotherapy. During the planned chemotherapy course, a right proximal thigh subcutaneous mass was incidentally found which on subsequent biopsy proved to be metastatic from rectal primary site. On subsequent 18F-FDG (Fluorodeoxyglucose) positron emission tomography (PET)/CT scan after completion of chemotherapy for the purpose of treatment response evaluation, only FDG-avid lesion was residual right proximal thigh metastatic mass without involvement of other common sites, such as liver and lung. In this case, the 18F-FDG-PET/CT scan was able to exclude additional metastatic sites and also evaluate the patient's treatment response.

Oropharyngeal Squamous Cell Carcinoma Metastasis to Distal Skeletal Muscle on FDG PET/CT

We present a case of a tongue squamous cell carcinoma (SCC) metastasizing to distal skeletal muscle detected on FDG PET/CT imaging. A 48-year-old man with locally recurrent tongue SCC underwent a restaging FDG PET/CT to investigate neck and unilateral leg pain. The PET scan showed large, intensely FDG-avid lesions in the right scalene and left hamstring muscles, which were biopsy proven as metastatic SCC. Skeletal muscle metastases from oropharyngeal SCCs are rare; however, PET/CT has allowed increased detection of atypical metastatic sites. Such cases support the consideration of metastasis for muscular lesions in head and neck cancer patients.

Relationship Between the Elevated Muscle FDG Uptake in the Distal Upper Extremities on PET/CT Scan and Prescan Utilization of Mobile Devices in Young Patients

It is common to notice increased FDG activity in the muscles of the forearms or hands on PET/CT images. The purpose of this study was to determine relationship between the prevalence of increased FDG activity in the forearms or hands and using mobile devices prior to the FDG PET/CT study.

METHODS

A total of 443 young patients with ages between 5 and 19 years who underwent FDG PET/CT scan were included in this retrospective analysis. All patients had FDG PET/CT with their arms within the field of views. The images were reviewed for elevated activity in the muscles of the distal upper extremities (DUEs), which include forearms and hands. The preimaging questionnaire/interview records regarding using mobile devices prior to FDG PET/CT were also reviewed and compared with the imaging findings.

RESULTS

Most patients (72.0% [319/443]) used mobile devices more than 60 minutes in the period of 24 hours prior to the FDG PET/CT study. Elevated uptake in the muscles in the DUEs was observed in 38.6% (123/319) of these patients. In contrast, among 124 patients who did not use the mobile devices or used the mobile device minimally prior to the study, only 6.5% (8/124) of them had elevated FDG activity in the DUEs. The difference persisted following stratification analysis for sex, age, and serum glucose level in our patient population.

CONCLUSIONS

Increased FDG uptake in the muscles of the DUEs in young patients is commonly seen in those who used mobile devices prior to PET/CT study. Recommendation should be considered to reduce using mobile devices prior to FDG PET/CT study in young patient population.

Improved detection of melanoma metastases by iodine maps from dual energy CT

OBJECTIVE

Metastatic disease in melanoma has an unpredictable nature with deposits in rare locations such as musculature. Dual energy CT (DECT) provides high contrast-visualization of enhancement by using spectral properties of iodine. Purpose of this study was to evaluate whether iodine maps from DECT improve lesion detection in staging examinations of melanoma patients.

METHODS

This retrospective study was approved by IRB and written informed consent was obtained from all patients. 75 contrast-enhanced DECT scans (thorax and abdomen) from 75 melanoma patients (n=69 stage IV; n=6 stage III) were analysed. For each patient, conventional CT and iodine maps were reviewed independently by two radiologists. The number of lesions detected by reviewing the iodine maps following conventional CT was recorded. Unweighted Cohens Kappa coefficient (κ) was used for concordance analysis, Wilcoxon test for comparing lesion detection rates.

RESULTS

In 26 patients, at least one reader found additional lesions on iodine maps (inter-reader agreement 89%, κ=0.74 (0.742-0.747)). Compared to grey-scale images, mean detection rate for metastases improved from 86% (range 82-90) to 94% (90-99%) (p≤0.01), for muscle metastases from 8% (8-8%) to 99% (98-100%) (p≤0.06). Findings included 2 pulmonary emboli.

CONCLUSION

Iodine maps from DECT improve detection of metastases, especially muscle metastases, and relevant findings in staging examinations of melanoma patients.

Long-term complete response in a breast cancer patient with skeletal muscle metastases diagnosed using 18F-FDG-PET

Common sites for metastatic spreading from breast cancer are bones, lungs and liver, the skeletal muscle being an unusual site. Although rare, when skeletal muscle metastases occur they are associated with a poor prognosis. These metastases are clinically difficult to diagnose since they can be found without pain symptoms. Radiologically, magnetic resonance imaging has been considered better than computed tomography for imaging of the muscles and has been the first procedure to use in case of muscle metastasis suspicion. In the last years, positron emission tomography (PET) with 18Fluorine-2-fluoro-2-deoxy-d-glucose (18F-FDG) has emerged as the main imaging tool. We here report a case of a hormone receptor-positive/human epidermal growth factor receptor 2-negative patient who presented with a recurrent infiltrating ductal carcinoma and diffuse skeletal muscle metastases detected by 18F-FDG-PET. The treatment of the patient with exemestane and everolimus led to a durable complete response.