Magnetic resonance imaging of intramuscular metastases

Diffusion weighted imaging demystified: the technique and potential clinical applications for soft tissue imaging

Diffusion-weighted imaging (DWI) is a fast, non-contrast technique that is readily available and easy to integrate into an existing imaging protocol. DWI with apparent diffusion coefficient (ADC) mapping offers a quantitative metric for soft tissue evaluation and provides information regarding the cellularity of a region of interest. There are several available methods of performing DWI, and artifacts and pitfalls must be considered when interpreting DWI studies. This review article will review the various techniques of DWI acquisition and utility of qualitative as well as quantitative methods of image interpretation, with emphasis on optimal methods for ADC measurement. The current clinical applications for DWI are primarily related to oncologic evaluation: For the assessment of de novo soft tissue masses, ADC mapping can serve as a useful adjunct technique to routine anatomic sequences for lesion characterization as cyst or solid and, if solid, benign or malignant. For treated soft tissue masses, the role of DWI/ADC mapping in the assessment of treatment response as well as recurrent or residual neoplasm in the setting of operative management is discussed, especially when intravenous contrast medium cannot be given. Emerging DWI applications for non-neoplastic clinical indications are also reviewed.

[Imaging characteristics of malignant and benign lesions of skeletal muscle]

There are many different tumors and tumor-like lesions with variable biological behavior that may affect the skeletal musculature. The aim of this study was to review the different intramuscular lesions and to provide a classification based on their radiological patterns. Intramuscular lesions can present as solid, liquid, semiliquid or fat equivalent manifestations and also as diffuse muscle enlargement and muscle calcification. Additionally, lesions with mixed patterns of the aforementioned alterations can also occur. Benign and malignant muscle lesions can often manifest with identical radiological patterns, which is why a certain differentiation is often difficult. A systematic radiological description and when possible assignment with respect to etiology and dignity depending on the patient history is necessary in order to recommend a subsequent histological confirmation or to avoid unnecessary confirmation.

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

OBJECTIVE

The aim of this study was to investigate the features and patterns of skeletal muscle metastases (SMM) detected with F-fluorodeoxyglucose (F-FDG) PET/computed tomography (PET/CT).

PARTICIPANTS AND METHODS

Our database was analyzed for patients with pathologically proven malignancy, who underwent F-FDG PET/CT in our institution. The patients with SMM were included in the study group on the basis of the final diagnosis confirmed by follow-up or histopathology. Images were acquired using a PET/CT system Biograph mCT S(64)-4R. CT was performed without contrast enhancement.

RESULTS

The selected group included 31 patients (1.7% of the database, which consisted of 1805 patients). A total of 233 lesions were found. The prevalence of SMM evaluated in specific primary malignancies was the highest in melanoma (6.9%), followed by carcinoma of unknown primary (4.4%), colorectal cancer (4.1%) and lung cancer (2.8%). Three patterns of skeletal muscle metastatic involvement were observed: multiple SMM accompanied by other metastases (64.5%), solitary lesion associated with other metastases (29%) and isolated intramuscular lesions (two cases, 6.5%). Isolated SMM represented recurrence of the malignant disease. In patients with extraskeletal metastases, solitary or multiple SMM did not affect tumor staging.

CONCLUSION

Solitary SMM are less common than multiple on F-FDG PET/CT imaging. SMM are usually associated with other metastases and do not affect tumor staging. The cases of isolated SMM are very rare. Nevertheless, in patients with a diagnosis of malignant disease, a solitary, F-FDG avid intramuscular focus should be suspected to represent metastasis.

Infiltrative pattern of carcinomatosis in extremity muscles on MRI

Carcinomas can cause an unusual, infiltrative pattern of metastatic carcinoma in extremity muscles on MRI. To assess this pattern, reports of MRI exams of 907 consecutive patients with a diagnosis of carcinoma were reviewed retrospectively to identify those that mentioned muscle metastasis or myositis in an extremity. Thirty-six (4%) of those reports described muscle metastasis (n=18) or myositis (n=18); based on medical record review and imaging follow-up, 17 cases represented metastases. Metastases manifested as an infiltrative carcinomatosis pattern in five patients, resulted from primary esophageal or gastric adenocarcinomas, and often were misdiagnosed as myositis.

Skeletal Muscle Metastasis from Renal Cell Carcinoma: 21 cases and review of the literature

OBJECTIVES

This study aimed to raise radiologists' awareness of skeletal muscle metastases (SMM) in renal cell carcinoma (RCC) cases and to clarify their imaging appearance.

METHODS

A retrospective analysis was undertaken of 21 patients between 44-75 years old with 72 SMM treated from January 1990 to May 2009 at the MD Anderson Cancer Center in Houston, Texas, USA. Additionally, 37 patients with 44 SMM from a literature review were analysed.

RESULTS

Among the 21 patients, the majority of SMM were asymptomatic and detected via computed tomography (CT). Mean metastasis size was 18.3 mm and the most common site was the trunk muscles (83.3%). The interval between discovery of the primary tumour and metastasis detection ranged up to 234 months. Peripheral enhancement (47.1%) was the most common post-contrast CT pattern and non-contrasted CT lesions were often isodense. Magnetic resonance imaging (MRI) characteristics were varied. Five lesions with available T1-weighted pre-contrast images were hyperintense to the surrounding muscle. Other organ metastases were present in 20 patients. Of the 44 SMM reported in the literature, the majority were symptomatic. Average metastasis size was 53.4 mm and only 20.5% of SMM were in trunk muscles. The average interval between tumour discovery and metastasis detection was 101 months. Other organ metastases were recorded in 17 out of 29 patients.

CONCLUSION

SMM should always be considered in patients with RCC, even well after primary treatment. SMM from RCC may be invisible on CT without intravenous contrast; contrast-enhanced studies are therefore recommended. SMM are often hyperintense to the surrounding muscle on T1-weighted MRI scans.

Comparison of ADC values in different malignancies of the skeletal musculature: a multicentric analysis

OBJECTIVE

Diffusion-weighted imaging (DWI) provides essential information regarding tumor composition, such as cellularity and/or perfusion. DWI is helpful in distinguishing between malignant and benign lesions. Malignant intramuscular/soft tissue lesions consist of a wide spectrum of tumors that have different cell counts and matrix. It is presumed that these different tumors have different DWI findings and have different apparent diffusion coefficient (ADC) values. The aim of this study was to analyze DWI findings of different intramuscular malignancies in a multicentric study by using a standardized DWI protocol, and to compare the ADC values acquired.

MATERIALS AND METHODS

The data banks of four radiology departments were screened retrospectively for malignant intramuscular tumors. Only lesions that were investigated by MRI (with a 1.5-T scanner) using DWI (multishot EPI sequence with b values of 0 and 1,000 s/mm(2)) were included in the study. Overall, 51 patients (28 women, 23 men; mean age 58.8 ± 16.1 years) with 57 different malignant intramuscular lesions were collected. In every case apparent diffusion constant (ADC) maps were calculated. In 14 patients muscle lymphoma, 11 patients intramuscular metastases from different primary tumors, and in 26 cases several muscle sarcomas were identified.

RESULTS

The mean ADC value of the estimated lesions was 1.24 ± 0.53 × 10(-3) mm(2)s(-1), median value, 1.11 × 10(-3) mm(2)s(-1), range, 0.54-2.9 × 10(-3) mm(2)s(-1). The mean ADC value in muscle metastases was 1.28 ± 0.24 × 10(-3) mm(2)s(-1), in muscle lymphoma 0.76 ± 0.14 × 10(-3) mm(2)s(-1), and in muscle sarcomas 1.82 ± 0.63 × 10(-3) mm(2)s(-1). Muscle lymphoma showed statistically significant lower ADC values in comparison to muscle metastases (p = 0.01) and muscle sarcoma (p = 0.001). There was no significant differences between ADC values in muscle metastases and sarcomas (p = 0.48). ADC values in muscle lymphoma were homogeneous with less inter-patient variability and were within a relatively close range. Muscle sarcomas had a broad range of ADC values.

CONCLUSION

Intramuscular malignant lesions had different ADC values on DWI. 22.8% of the tumors analyzed had low ADC values, 26.3% moderate, and 50.9% high ADC values. Muscle lymphoma had statistically significantly lower ADC values in comparison to muscle metastases and sarcomas. Muscle sarcomas presented with a broad range of ADC values.

Non-Hodgkin's Lymphoma of Multiple Skeletal Muscles Involvement Seen on FDG PET/CT Scans

As normal healthy skeletal muscle does not contain lymphoid tissue, extra nodal lymphoma involving multiple muscles is rare, as well. This study reports a case of non-Hodgkin's lymphoma (NHL) of multiple skeletal muscles involvement and a review of differential diagnosis of it.A 37-year-old female presented to our hospital after being diagnosed with NHL for 7 months. She had received six courses of cyclophosphamide hydroxydaunorubicin oncovin prednisolone etoposide (CHOPE) chemotherapy. Then she felt pain and noticed swelling on her left calf. The fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) image showed abnormal focal FDG uptake in hypo-pharynx, which was the primary NHL and also in multiple groups of muscles in whole body. As the patient has history NHL, lymphoma of multiple muscle involvement was suspected.Finally, an ultrasound-guided tissue biopsy was performed on the left calf and histological examination yielded lymphomatous cells infiltration in the left gastrocnemius.Through this report, we emphasize that a multidisciplinary team approach with clinician, radiologist, and pathologist is essential for proper diagnosis, staging, and management of such rare lesions.

Rotator cuff metastases: a report of two cases with literature review

Context:

Distant metastases of primary malignancies to the skeletal muscle tissue are a very rare event. Distant metastases that affect the rotator cuff are even rarer, and only a few of cases have been reported so far.

Case Report:

The present article reports two cases that presented to our hospital with the complaint of shoulder pain and had a soft tissue mass affecting the muscles of the rotator cuff and invading the neighboring bone compartments. One of the patients developed mucoepidermoid cancer metastasis of the submandibular gland, and the other was found to have a malignant epithelial tumor metastasized from the lower lobe of the right lung, whose primary origin could not be diagnosed until the imaging examinations were employed. Ultrasound and magnetic resonance imaging findings are presented in this paper.

Conclusion:

Metastases to the muscle tissues could be misdiagnosed as primary sarcomas. Because the therapy regiments and prognoses are fairly different for these two entities, the possibility of a metastasis to the muscle tissue must be considered as a differential diagnosis for case of painful soft tissue mass. Ultrasound is very useful in detection of the lesion and acts as a very important tool during guidance for biopsy. Magnetic resonance imaging, however, is a very valuable asset in the evaluation of the borders of the soft tissue mass and its invasive effect on the bony tissues. Particularly when the features such as lobulated contours, peripheral edema, and intratumoral necrosis exist, the possibility of metastases must be considered.

Metastasis of gastrointestinal stromal tumor to skeletal muscle: a case report

Introduction

Gastrointestinal stromal tumor is the most common malignant mesenchymal tumor of the gastrointestinal tract. The most common sites of metastasis are the liver and the peritoneum, but gastrointestinal stromal tumors rarely metastasize to the skeletal muscles. Only three cases of gastrointestinal stromal tumor metastasizing to skeletal muscle have been reported in the English literature. Here we present an additional case of skeletal muscle metastasis, and the relevant literature is reviewed.

Case presentation

A 54-year-old Japanese man presented with a three-month history of an enlarging mass of the left buttock. An excisional biopsy was performed and the tumor was diagnosed as a leiomyosarcoma. However, careful examination of the gastrointestinal tract revealed a tumor located in the small intestine. Surgical resection of the small intestine tumor was performed; histopathological and immunohistochemical examinations identified it as a primary gastrointestinal stromal tumor arising from the small intestine. Despite receiving both chemotherapy and molecular-targeted therapy, our patient died of gastrointestinal bleeding six months after the initial diagnosis.

Conclusions

Because it is a mesenchymal tumor, it is difficult to distinguish a gastrointestinal stromal tumor metastasis to skeletal muscle from other primary soft tissue sarcomas. Although metastasis of gastrointestinal stromal tumor to skeletal muscle is rare, the likelihood of finding metastases in these unusual sites is increasing due to prolonged survival of patients with gastrointestinal stromal tumor after the introduction of imatinib therapy. We should include metastases of gastrointestinal stromal tumors as differential diagnosis of spindle cell tumor, and it is necessary to begin appropriate treatment early.

Diffusion-weighted imaging of skeletal muscle lymphoma

OBJECTIVE

Muscle lymphoma (ML) is a relatively uncommon condition. On magnetic resonance imaging (MRI), ML can manifest with a broad spectrum of radiological features. The aim of this study was to demonstrate the features of DW images of muscle lymphoma (ML).

MATERIALS AND METHODS

In our database, ten patients (six women and four men) with ML were identified who were investigated by magnetic resonance imaging including acquisition of DW images. DW images were obtained using a multi-shot SE-EPI pulse sequence. Apparent diffusion constant (ADC) maps were also calculated. Furthermore, fusion images were generated manually from DW and HASTE or T2W images.

RESULTS

On T2W images, all recognized lesions were hyperintense in comparison to unaffected musculature and on T1W images they were homogeneously hypointense. All lesions demonstrated low signal intensity on ADC images. The calculated ADC values ranged from 0.60 to 0.90 mm(2)s(-1) (mean value 0.76 ± 0.10; median value 0.78). On fusion images, all lesions showed high signal intensity.

CONCLUSIONS

ML demonstrated low ADC values and high signal intensity on fusion images suggesting high cellularity of the lesions.

Malignant and benign lesions of the skeletal musculature

There are several tumors and tumorlike conditions with variable biological behavior that may involve the skeletal musculature. The aim of this work was to review different intramuscular lesions and to provide a classification of muscle lesions based on their radiological patterns as well as to provide as a pictorial essay the imaging characteristics of typical muscle lesions. Radiologically, intramuscular lesions can manifest as solid masses, liquid or semiliquid masses, fat-containing lesions, diffuse muscle enlargement, and muscle calcifications. Additionally, lesions with mixed patterns can also occur. It is noteworthy that different malignant or benign muscle lesions can manifest with identical radiological patterns.

Magnetic resonance imaging of pelvic metastases in male patients

Magnetic resonance (MR) imaging offers a noninvasive tool for diagnosis of primary and metastatic pelvic tumors. The diagnosis of a pelvic metastatic lesion implies an adverse prognosis and dictates the management strategies. Knowledge of normal MR imaging anatomy of the pelvis and the signal characteristics of normal and abnormal structures is essential for accurate interpretation of pelvic MR imaging. This article reviews imaging manifestations of nodal, visceral, and musculoskeletal metastatic lesions of the pelvis along with current and evolving MR imaging techniques.

Muscle metastases: comparison of features in different primary tumours

Background

Muscle metastases (MM) from solid tumours are rare. The aim of this study was to describe radiological features of MM, and to compare their patterns in different malignancies.

Methods

A retrospective search in the statistical database of our institution revealed 61 cases of MM. Additionally, a retrospective search in Pubmed database was performed. Together with our cases the present analysis comprises 461 patients (682 MM).

Results

MM derived from the following malignancies: lung cancer (25.1%), gastrointestinal tumours (21.0%), and urological tumours (13.2%). Other neoplasias with MM were rare. MM were localised most frequently in the thigh muscles, the extraocular musculature, and the gluteal and paravertebral muscles. The localisation of MM was different in several primary malignancies.

On computed tomography (CT), five different patterns of MM occurred: masses with homogeneous contrast enhancement (type I, 46.5%), abscess-like lesions (type II, 27.7%), diffuse infiltration with muscle swelling (type III, 18.1%), intramuscular calcifications (type IV, 6.5%), or MM presented as intramuscular bleeding (type V, 1.2%). MM from several primary tumours manifested with different CT patterns.

On MRI, most MM were hyperintense in comparison to unaffected musculature in T2 weighted images and hypo- to isointense on T1 weighted images with a heterogeneous enhancement. There were no differences in MRI features of MM in different primary tumours. On ultrasound, most MM were hypoechoic. On positron emission tomography, MM presented as focally abnormal intramuscular uptake.

Conclusion

MM present with a broad spectrum of radiological features. Different CT imaging findings of MM were observed in different primary tumours. The localisation of MM also varies with different primary malignancies.

PET/CT imaging of skeletal muscle metastases

BACKGROUND

Skeletal muscle metastases (SMM) are very rare because of complex resistance of the musculature to metastatic invasion. Previously, positron emission tomography (PET) imaging of SMM has been reported only in few reports. A systematic analysis of SMM features in PET/CT has not been performed before.

PURPOSE

To study PET/CT findings of SMM in a larger group of patients with known malignancies and to determine PET/CT patterns of SMM in different primary tumors.

MATERIAL AND METHODS

Between January 2009 and December 2011 581 patients with lung cancer were investigated by PET with 18 F-fluordeoxyglucose (FDG PET) and computed tomography (CT) at the Center of Fusion Imaging, Halle. In five patients SMM were identified. Furthermore, PubMed database was screened for muscle metastases. Only articles containing SUV of SMM were considered in the study. Twenty-one articles with 33 patients could be included in this meta-analysis from the literature.

RESULTS

At our center the prevalence of SMM was 0.9%. Our analysis comprised 38 patients with 67 muscle metastases. All identified SMM presented as intramuscular focal abnormal activity with SUV ranging from 2.4 to 25.9, median SUV 7.8. The median size of the muscle metastases was 2.5 cm (range, 0.6-6.5 cm). There were no significant differences between SUV and size of SMM arising from lung cancer, renal cell carcinoma, and esophageal cancer. Also, there was no correlation between SUV and size of SMM (r = 0.101, P = 0.558) and between SUV of SMM and primary tumors (r = 0.138, P = 0.686). In nine (23.7%) of the 38 patients, the identified SMM were isolated distant metastases or isolated tumor recurrence.

CONCLUSION

SMM manifested on PET/CT as focal hypermetabolic intramuscular areas with different SUV. There were no significant differences between SUV or size of the identified SMM in esophageal cancer, renal cell carcinoma, and lung cancer.

Usefulness of a half-fourier acquisition single-shot turbo spin-echo pulse sequence in identifying arachnoid diverticula in dogs

Single-shot turbo spin-echo sequences are heavily T2-weighted sequences that are exceptionally well suited to evaluate the subarachnoid space. In the T2-weighted fast spin-echo sequences that are used routinely in spinal magnetic resonance (MR) imaging, the subarachnoid space is not well differentiated from the surrounding epidural fat, which could lead to decreased detection of lesions of the subarachnoid space such as arachnoid diverticula. Our purpose was to determine the added value of a single-shot turbo spin-echo sequence in identifying cystic lesions of the subarachnoid space in dogs. MR images of six dogs with a confirmed arachnoid diverticulum and 24 dogs with other spinal disease were included. Six observers were asked to interpret only T2-weighted images initially, and in a second session, T2-weighted and half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequences. The MR images were anonymized, and no signalment, history, or clinical information was provided. Without the HASTE sequences, 25% of arachnoid diverticula were identified. Adding the HASTE sequence increased the diagnosis of arachnoid diverticulum to 52.8%. The resulting difference, after adding the HASTE sequence, of 27.8% was statistically significant (P = 0.002). No false-positive diagnoses of arachnoid diverticulum were made with either sequence. Although sensitivity in this study was likely artificially low, the significantly increased detection rate of arachnoid diverticula when using HASTE imaging indicates that this sequence is a valuable addition to MR imaging protocols for the canine spine.

Intramuscular metastases on FDG PET-CT: a review of the literature

OBJECTIVE

Intramuscular metastases (IM) are both rare and difficult to detect using routine anatomical computed tomography (CT) imaging. However, since the introduction of 18F-fluoro-deoxy-glucose (FDG) PET-CT, the number of detected IM has increased. We review the available literature to illustrate the relevance of these findings for staging and patient management.

METHODS

In a review of the literature, we found one series and 33 case reports of IM shown on FDG PET-CT. No cases were reported before 2005. Furthermore, we present a patient with nonsmall cell lung cancer and a solitary distant metastasis in the left musculus infraspinatus that was not detected on diagnostic CT, but was found on FDG PET-CT.

RESULTS

For a total of 39 recorded cases of IM, we found that FDG PET-CT had a significant impact on patient management in at least 51% of cases. Where reported, lesions were either isodense or hypodense on CT compared with the surrounding muscle tissue. The lesions that were also analyzed with MRI showed heterogeneous intensity. Five out of 39 patients had metastases in the extraocular muscles of one or both orbits.

CONCLUSION

FDG PET-CT appears to be a sensitive tool for detecting IM, with important impact on management in many cases.