1992, The British Journal of Radiology, 65, 485-490
Intramuscular myxoma: magnetic resonance features By Abrahim Fikry Abdelwahab, MD, *Samuel Kenan, MD, George Hermann, MD, 'Michael M. Lewis, MD and tMichael J. Klein, MD Departments of Radiology, 'Orthopaedic Surgery and tPathology, Mount Sinai Medical Center, New York, USA {Received 2 September 1991 and in revised form 2 January 1992, accepted 13 January 1992) Keywords: Soft-tissue tumours, Intramuscular myxoma, Magnetic resonance imaging
Abstract. Magnetic resonance imaging (MRI) was performed in six cases of intramuscular myxoma of the extremities and revealed the following characteristics. All tumours were confined to muscle and had a sharply defined border. All had a signal intensity lower than skeletal muscles on r r weighted images and brighter than fat on r r weighted images. The signals were homogeneous on both Tr and r2-weighted images. This study did not include contrast enhancement. The diagnosis was confirmed by an open biopsy. All tumours were resected with no recurrence. Diagnosis based on these MRI characteristics was incorrect in two cases of intramuscular ganglia and in a case of intramuscular cysticercus cellulose. MRI features of intramuscular myxoma are typical in the majority of cases. Benign intramuscular lesions that contain mainly fluid can mimic intramuscular myxomas.
Intramuscular myxoma is a distinct benign tumour. The diagnostic efficacy of magnetic resonance imaging (MRI), a multiplanar imaging technique, compared with computed tomography (CT) has proved to be superior in the detection and evaluation of soft-tissue masses (Petasnick et al, 1986; Petterson et al, 1987; Wetzel et al, 1987). Certain criteria favour benign softtissue tumours, which include sharp definition of the margin, lack of septation and homogeneity in signal intensity (Sundaram et al, 1988; Kransdorf et al, 1989a; Berquist et al, 1990).
sies and the resected tumours were studied by a bone pathologist. The diagnosis of intramuscular myxoma was considered from the MRI scans and was based on the intramuscular site of the lesions, the sharp definition of the margin, the characteristic signal intensities and the homogeneity of the signals. All the patients had an open biopsy followed by total excision of the tumour. All patients were followed up every 3 months. Three patients were followed for more than 3 years, two for less than 2 years and the sixth patient for more than 6 months with no evidence of recurrence.
Materials and methods
These cases were referred over a five-year period to our orthopaedic tumour service, which functions as a tertiary referral centre for patients with bone or softtissue tumour in New York City. These patients were investigated, including MRI scans, by their private physicians before they were referred to us. There were two male and four female patients ranging in age from 36 to 65 years, with a mean of 49 years. The MRI scans were performed by different scanners ranging from 0-5 T to 1.5 T. Scanning sequences included spin-echo r r weighted 300-600/20-30 TR/TE (time to repeat/time to echo) and T2-weighted, 2000-2600/80-100 pulse sequences. Section thickness varied from 4 to 10 mm. At least two orthogonal planes were imaged, and in two patients imaging was in three planes. All the MRI scans were without contrast enhancement or short 7\ inversion-recovery sequence (STIR). The scans were reviewed by a musculoskeletal radiologist. Open biopAddress correspondence to Ibrahim Fikry Abdelwahab, MD, Department of Radiology, Box 1234, Mount Sinai Medical Center, 1 Gustave L. Levy Place, New York, NY 10029-6574, USA.
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Case histories Case 1 A 40-year-old white female noticed a painless lump in the left shoulder for 2 weeks. Physical examination revealed a non-tender, 2 cm x 4 cm well demarcated mass in the region of the deltoid muscle. There were no skin changes. The MRI scan revealed an oval mass lesion in the left deltoid muscle (Fig. 1). Case 2 A 65-year-old white female presented with a lump in the posterior aspect of the right shoulder, which she noticed 3 weeks earlier. Physical examination revealed a non-tender, 6 cm x 8 cm mass in the infraspinatus region of the right scapula. There was full range of movement of the right shoulder. MRI revealed a well circumscribed oval mass in the infraspinatus muscle. Case 3 A 48-year-old white female noted a painless left gluteal mass for 1 year, which grew slowly during this period. Clinical examination revealed a 3 cm x 5 cm, non-tender, deeply seated left gluteal mass. There was 485
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Figure 1. MRI of the left shoulder, (a) Axial 7,-weighted image (TR 400/TE 20) and (b) axial r r weighted image (TR 2000/TE 80). MRI reveals an oval, sharply defined lesion in the left deltoid muscle with hypointense signal on the r,-weighted image and bright signal on the r2-weighted image. Both signals are homogeneous.
no neurovascular deficit. MRI revealed an oval mass in the left gluteus maximus (Fig. 2). Case 4 A 38-year-old black female noted 3 months earlier a painless, deeply seated mass in the proximal part of the right thigh. Physical examination revealed full range of movement of the right hip and knee without neurological deficit. A firm, mobile, non-tender mass, 4 cm x 8 cm, was felt in the proximal anteromedial part of the right thigh. MRI showed the mass to be in the vastus medialis (Fig. 3). Case 5 A 65-year-old Asian male presented with a 6-month history of a firm, painless mass on the medial aspect of
the left thigh. Physical examination revealed an oval, non-tender mass approximately 4 cm x 5 cm in its greatest diameter located in the mid-thigh in the region of the adductor muscles. The overlying skin and the neuro vascular bundle were intact. MRI revealed the mass to be in the semimembranosus muscle (Fig. 4). Case 6 A 36-year-old white male presented with a mass in the anterolateral aspect of the left knee just proximal to the patella, noticed 1 year earlier. Lately the mass became painful during walking and climbing stairs. A laminectomy had been performed 12 years earlier. Physical examination revealed a firm nodule on the lateral aspect of the quadriceps tendon approximately 3 cm proximal to the patella. The mass was mobile and slightly tender
Figure 2. MRI of the left buttock, (a) Axial 7>weighted image (TR 570/TE 20) and (b) axial 7>weighted image (TR 2000/TE 85). MRI demonstrates an oval, sharply defined mass in the left gluteus maximus, which has a low signal intensity on the T,-weighted image and high signal intensity on the T2-weighted image with homogeneity in both signals.
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Intramuscular myxoma: magnetic resonance features
Figure 3. MRI of the right thigh, (a) Coronal r,-weighted image (TR 600/TE 20) and (b) axial r r weighted image (TR 2000/TE 60). MRI shows an oval lesion that has sharp borders in the vastus medialis muscle with homogeneous hypointense signal on the Tx -weighted image and homogeneous bright signal on the T2- weigh ted image.
on deep palpation. It was attached neither to the skin nor to the bone. There was a full range of movement in the hip and knee. MRI revealed the mass to be in the quadriceps muscle. Discussion Although the superiority of MRI over CT in evaluating soft-tissue masses is well established, the specificity of MRI in the histological diagnosis of these tumours is less than 20% (Kransdorf et al, 1989a). Tumours with substantial amounts of myxoid tissue may be benign as intramuscular myxomas or they may Vol. 65, No. 774
be malignant tumours undergoing myxomatous degeneration. The majority of intramuscular myxomas occur between the fourth and seventh decades They are less commonly encountered in young adults and rarely in children (Ireland et al, 1973; Canalis et al, 1976; Kransdorf et al, 1989b). The mean age in our cases was 49 years. There is a slight female predominance (Canalis et al, 1976); four of our six patients were women. The most common site of myxoma is the heart (Stout, 1948). If we eliminate bony myxomas, which are almost exclusively in the jaws with only a few cases reported in the long tubular bones and pelvis (Stout, 1948; Ireland et al, 1973; Canalis et al, 1976; McClure & Dahlin, 1977; Abdelwahab et al, 1991), the majority of extracardiac soft-tissue myxomas occur in the musculature of the extremities, particularly of the thigh and shoulder girdle (Stout, 1948; Enzinger, 1965; Ireland et al, 1973). Three of our cases occurred in the thigh and two in the shoulder. To date, the total number of intramuscular myxomas is less than 150 (Canalis et al, 1976; McCook et al, 1981). The tumour usually presents as a painless mass. About 20% of patients are symptomatic, complaining of pain and/or tenderness (Enzinger, 1965). The rate of tumour growth is variable, and occasionally there is no apparent growth over long periods of time (Kransdorf et al, 1989b). It is rare for the tumour to be clinically diagnosed before MRI or biopsy. There has been no documented case of metastasis (Shugar et al, 1987). In 1948, Stout defined the myxoma as a true mesenchymal neoplasm composed of undifferentiated stellate cells in myxoid stroma. Enzinger (1965), reviewing softtissue myxomas but excluding cardiac myxomas, found that one of every six myxomas was located in muscle. On gross inspection, the tumour is oval or spherical in shape, and when cut open presents a white or grey-white mucoid, gelatinous surface. Small cyst-like spaces or traversing trabeculae are not uncommon. On close inspection, the delicate fibrous capsule is usually incomplete and practically all lesions infiltrate adjacent muscles. Microscopically, myxoma is composed of stellate cells and a meshwork of reticulum fibres in a matrix of mucoid material that contains hyaluronic acid (Stout, 1948; Kindbloom et al, 1974) (Fig. 5). Although Stout stated that the recurrence rate was high after resection of these tumours, other reports, including ours, have not confirmed this (Enzinger, 1965; Kindbloom et al, 1974; Feldman, 1979). There is an association between intramuscular myxomas and fibrous dysplasia (Ireland et al, 1973; Sundaram et al, 1989). Wirth et al (1971) described this association as a syndrome in which intramuscular myxomas are an extraskeletal manifestation of fibrous dysplasia. The majority of tumours are associated with polyostotic fibrous dysplasia (Wirth et al, 1971; Logel, 1976; Dahlin, 1987). The intramuscular myxomas are usually located in the vicinity of the most severely affected bones and most often occur in the thigh and may be multiple. Half of the patients had some manifestation of Albright's syndrome (Logel, 487
/. F. Abdelwahab, S. Kenan, G. Hermann, M. M. Lewis and M. J. Klein
Figure 4. MRI of the left thigh, (a) Axial T.-weighted image (TR 500/TE 30) and (b) axial J2-weighted image (TR 2000/TE 60). MRI reveals an oval lesion with sharp borders in the semimembranosus muscle, which has low signal intensity on the r r weighted image and high signal intensity on the r r weighted image. Both signals are uniform.
1976). To date, there are less than 20 cases of intramuscular myxomas associated with fibrous dysplasia. Of these, only two cases were associated with monostotic fibrous dysplasia (Ireland et al, 1973; Sundaram et al, 1989). The possibility of associated fibrous dysplasia when an intramuscular myxoma is discovered should always be considered. Our six cases were not associated with fibrous dysplasia. Intramuscular myxomas are rare tumours. In three large series of soft-tissue tumours studied by MRI, totalling 258, there were only three intramuscular myxomas (Sundaram et al, 1988; Kransdorf et al, 1989a; Berquist et al, 1990). There are also sporadic case
reports of intramuscular myxomas in which MRI was performed (Kransdorf et al, 1989b; Sundaram et al, 1989). Our series of six intramuscular myxomas seems to be the largest studied by MRI. The characteristic pattern of MRI was typical in all our cases. However, our experience differed from other authors. In a recent report by Peterson et al (1991), although three of their four cases of intramuscular myxomas demonstrated the typical MRI characteristics, one case that was homogeneous on both Tx- and T2weighted images demonstrated, only after contrast enhancement, an irregular contrast enhancement in only one of the two components of the lesion. Part of the
(a) Figure 5. Photomicrographs, (a) A low-power view demonstrating loose textured, avascular myxoid tissue of the tumour (left and centre). A fibrous capsule separates the lesion from the skeletal muscle fibres (right) ( x 11). (b) A high-power view reveals spindle and stellate cells with long processes in a loose acellular myxoid stroma ( x 113).
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Intramuscular myxoma: magnetic resonance features
Figure 6. MRI of the right leg. (a) Coronal r,-weighted image (TE 400/TE 20) and (b) axial T2-weighted image (TR 1800/TE 60). The coronal slice reveals an oval, sharply defined lesion in the proximal part of the right leg with low signal intensity. Note the stalk between the lesion and the superior tibiofibular joint. The signal is bright on the r2-weighted image. The above appearances are characteristic of an intramuscular ganglion.
border was also not sharply denned. In one of two cases of intramuscular myxomas reported by Kransdorf et al (1989b), MRI revealed on 7> and T2-weighted pulse sequences an area of increased signal intensity in the distal aspect of the tumour similar to subcutaneous fat. As fluid and myxoid tissue have the same MRI characteristics, our diagnosis was incorrect in three rare benign lesions that contained mainly fluid. Two were intramuscular ganglia in the proximal part of the leg, which communicated with the synovium of the knee joint by a thin duct-like structure lined by single, flattened endothelial cells. Retrospective study of the MRI of the intramuscular ganglia revealed, in the cuts performed in the coronal plane, the tract between the ganglion and the knee joint (Fig. 6). We, therefore, emphasize performing MRI in the coronal planes, particularly when fluid-containing lesions are close to the joints. The third lesion was an intramuscular cysticercus cellulose located in the brachioradialis muscle of the right forearm in a Middle Eastern young male. The lesion contained gelatinous fluid. Acute haematoma containing fresh blood can mimic myxoma, although there is usually a history of trauma with a Vol. 65, No. 774
painful tender swelling. Intramuscular abscess usually has inhomogeneous signal intensity, depending on the amount of protein and necrotic debris within the abscess, with oedema in the surrounding tissue. Schwannomas are attached to the nerve roots outside the muscles, but if large, may compress the surrounding muscles and may simulate myxoma. However, they are usually more hyperintense than the muscle on r,-weighted images and have areas of decreased signal intensity on r2-weighted images. Some malignant softtissue tumours, namely liposarcomas, chondrosarcoma and malignant fibrous histiocytomas, may undergo myxomatous degeneration and may demonstrate a high signal intensity on T2-weighted images, simulting intramuscular myxomas. However, these tumours usually lack the uniformity of the signal intensity and usually have septations on r2-weighted images (Kransdorf et al, 1989a; London et al, 1989). Myxoid liposarcomas constitute approximately 50% of liposarcomas. They show amorphous or linear foci of high signal within a low signal mass on Trweighted images and one should consider this possibility even if the tumour otherwise appears benign (Sundaram et al, 1990). Occasionally, a 489
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malignant tumour may have a homogeneous signal intensity with a sharply defined margin. A signal intensity on a r,-weighted image greater than muscle or if the tumour is extramuscular, may differentiate them from myxomas. We conclude that MRI characteristics of intramuscular myxomas are typical in the majority of cases and that benign lesions which contain mainlyfluidmay mimic intramuscular myxomas. On the other hand, malignant soft-tissue tumours with myxomatous degeneration can be differentiated by the heterogeneity of the signal intensity on both T{- and T2- weigh ted images and the presence of septations. Acknowledgments The authors wish to thank Thomas A. Einhorn, MD, for Case 1 and Herbert S. Sherry, MD, for Case 3. References ABDELWAHAB, I. F., HERMANN, G., KLEIN, M. J., KENAN, S. &
S. W., BENTON, P. C. & BERRY, B. H., 1989b. Intramuscular
myxoma: MR features. Journal of Computer Assisted Tomography, 13, 836-839. LOGEL, R. J., 1976. Recurrent intramuscular myxoma associated with Albright's syndrome. Case report and review of the literature. Journal of Bone and Joint Surgery, 58A, 565-568. LONDON, J., KIM, E. E., WALLACE, S., SHIRKODA, A., COAN, J.
& EVANS, H., 1989. MR imaging of liposarcoma. Correlation of MR features and histology. Journal of Computer Assisted Tomography, 12, 832-835. MCCLURE, D. K. & DAHLIN, D. C , 1977. Myxoma of bone.
Report of three cases. Mayo Clinic Proceedings, 52, 249-253. MCCOOK, T. A., MARTINEZ, S., KOROBKIN, M., RAM, P. C , BOWEN, J. H., BREIMAN, R. S., HARRELSON, J. M. &
GEHWEILER, J. A. JR, 1981. Intramuscular myxoma. Radiographic and computed tomographic findings with pathologic correlation. Skeletal Radiology, 7, 15-19. PETASNICK, J. P., TURNER, D. A., CHARTERS, J. R., GITELIS, S.
& ZACHARIAS, C , 1986. Soft tissue masses of the locomotor system: comparison of MRI with CT. Radiology, 160, 125-133. Skeletal
PETERSON, K. K., RENFEW, D. L., FEDDERSEN, R. M., BUCKWALTER, J. A. & EL-KOURY, G. Y., 1991. Magnetic
BERQUIST, T. H., ETHAN, R. L., KING, B. F., HODGMAN, C. G.
resonance imaging of myxoid containing tumors. Skeletal Radiology, 20, 245-250.
LEWIS, M. M., 1991. Fibromyxoma of bone. Radiology, 20, 95-98.
& ILSTRUP, D. M , 1990. Value of MR imaging in differentiating benign from malignant soft tissue masses: study of 95 lesions. American Journal of Roentgenology, 155, 1251-1255. CANALIS,
R. F.,
SMITH, G. A.
& KONRAD, H. R.,
1976.
Myxoma of the head and neck. Archives of Otolaryngology, 102, 300-305. DAHLIN, D. C , 1987. Polyostotic fibrous dysplasia associated with myxoma of the soft tissues. Presented at the closed meeting of the International Skeletal Society, Cannes, France, September 1987. ENZINGER, F. M., 1965. Intramuscular myxomas, a review and follow-up study of 34 cases. American Journal of Clinical Pathology, 43, 104-113. FELDMAN, P. S., 1979. A comparative study including ultrastructure of intramuscular myxoma and myxoid liposarcoma. Cancer, 43, 512-525. IRELAND, D. C. R., SOULE, E. H. & IOINS, J. E., 1973. Myxoma
of somatic soft tissues. A report of 58 patients, 3 with multiple tumors and fibrous dysplasia of bone. Mayo Clinic Proceedings, 48, 401-410. KINDBLOOM,
L. G.,
STENER, B. & ANGERVALL, L.,
1974.
Intramuscular myxoma. Cancer, 34, 1737-1744. KRANSDORF, M. J., JELINEK, J. S., MOSER, R. P., JR, U T Z , J. A., BROWER, A. C , HUDSON, T. M. & BERRY, B. H.,
1989a. Soft tissue masses: diagnosis using MR imaging. American Journal of Roentgenology, 153, 541-547. KRANSDORF, M. J., MOSER, R. P., J R , JELINEK, J. S., WEISS,
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PETTERSON, H., GILEPSY, T., HOUNLIN, D. J., ENNEKING, W. F., SPRINGFIELD, D. S., ANDREW, R. E., SPANIER, S. & STONE,
R., 1987. Primary musculoskeletal tumors: examination with MR imaging compared with conventional modalities. Radiology, 164, 237-241. SHUGAR, J. M., SOM, P. M., MEYERS, R. J. & CHAEFFER, B. T.,
1987. Intramuscular head and neck myxoma. Report of a case and review of the literature. Laryngoscope, 97, 105-107. STOUT, A. P., 1948. Myxoma, a tumor of primitive mesenchyme. Annals of Surgery, 127, 706-719. SUNDARAM, M . , BAREN, G., MERAND, G . & MCDONALD, D . J.,
1990. Myxoid liposarcoma: magnetic resonance imaging appearances with clinical and histologic correlation. Skeletal Radiology, 19, 359-362. SUNDARAM, M., MCDONALD, D. J. & MERAND, G., 1989.
Intramuscular myxoma: a rare but important association with fibrous dysplasia of bone. American Journal of Roentgenology, 153, 107-108. SUNDARAM, M., MCGUIRE, M. H. & HERBOLD, D. R., 1988.
Magnetic resonance imaging of soft tissue masses. An evaluation of fifty-three histologically proven tumors. Magnetic Resonance Imaging, 6, 237-248. WETZEL, L. H., LEVINE, E. & MURPHEY, M. D., 1987. A
comparison of MR imaging and CT in the evaluation of musculoskeletal masses. Radiographics, 7, 851-874. WIRTH,
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Multiple intramuscular myxomas. Another extraskeletal manifestation of fibrous dysplasia. Cancer, 27, 1167-1173.
The British Journal of Radiology, June 1992
Intramuscular myxoma: magnetic resonance features By Abrahim Fikry Abdelwahab, MD, *Samuel Kenan, MD, George Hermann, MD, 'Michael M. Lewis, MD and tMichael J. Klein, MD Departments of Radiology, 'Orthopaedic Surgery and tPathology, Mount Sinai Medical Center, New York, USA {Received 2 September 1991 and in revised form 2 January 1992, accepted 13 January 1992) Keywords: Soft-tissue tumours, Intramuscular myxoma, Magnetic resonance imaging
Abstract. Magnetic resonance imaging (MRI) was performed in six cases of intramuscular myxoma of the extremities and revealed the following characteristics. All tumours were confined to muscle and had a sharply defined border. All had a signal intensity lower than skeletal muscles on r r weighted images and brighter than fat on r r weighted images. The signals were homogeneous on both Tr and r2-weighted images. This study did not include contrast enhancement. The diagnosis was confirmed by an open biopsy. All tumours were resected with no recurrence. Diagnosis based on these MRI characteristics was incorrect in two cases of intramuscular ganglia and in a case of intramuscular cysticercus cellulose. MRI features of intramuscular myxoma are typical in the majority of cases. Benign intramuscular lesions that contain mainly fluid can mimic intramuscular myxomas.
Intramuscular myxoma is a distinct benign tumour. The diagnostic efficacy of magnetic resonance imaging (MRI), a multiplanar imaging technique, compared with computed tomography (CT) has proved to be superior in the detection and evaluation of soft-tissue masses (Petasnick et al, 1986; Petterson et al, 1987; Wetzel et al, 1987). Certain criteria favour benign softtissue tumours, which include sharp definition of the margin, lack of septation and homogeneity in signal intensity (Sundaram et al, 1988; Kransdorf et al, 1989a; Berquist et al, 1990).
sies and the resected tumours were studied by a bone pathologist. The diagnosis of intramuscular myxoma was considered from the MRI scans and was based on the intramuscular site of the lesions, the sharp definition of the margin, the characteristic signal intensities and the homogeneity of the signals. All the patients had an open biopsy followed by total excision of the tumour. All patients were followed up every 3 months. Three patients were followed for more than 3 years, two for less than 2 years and the sixth patient for more than 6 months with no evidence of recurrence.
Materials and methods
These cases were referred over a five-year period to our orthopaedic tumour service, which functions as a tertiary referral centre for patients with bone or softtissue tumour in New York City. These patients were investigated, including MRI scans, by their private physicians before they were referred to us. There were two male and four female patients ranging in age from 36 to 65 years, with a mean of 49 years. The MRI scans were performed by different scanners ranging from 0-5 T to 1.5 T. Scanning sequences included spin-echo r r weighted 300-600/20-30 TR/TE (time to repeat/time to echo) and T2-weighted, 2000-2600/80-100 pulse sequences. Section thickness varied from 4 to 10 mm. At least two orthogonal planes were imaged, and in two patients imaging was in three planes. All the MRI scans were without contrast enhancement or short 7\ inversion-recovery sequence (STIR). The scans were reviewed by a musculoskeletal radiologist. Open biopAddress correspondence to Ibrahim Fikry Abdelwahab, MD, Department of Radiology, Box 1234, Mount Sinai Medical Center, 1 Gustave L. Levy Place, New York, NY 10029-6574, USA.
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Case histories Case 1 A 40-year-old white female noticed a painless lump in the left shoulder for 2 weeks. Physical examination revealed a non-tender, 2 cm x 4 cm well demarcated mass in the region of the deltoid muscle. There were no skin changes. The MRI scan revealed an oval mass lesion in the left deltoid muscle (Fig. 1). Case 2 A 65-year-old white female presented with a lump in the posterior aspect of the right shoulder, which she noticed 3 weeks earlier. Physical examination revealed a non-tender, 6 cm x 8 cm mass in the infraspinatus region of the right scapula. There was full range of movement of the right shoulder. MRI revealed a well circumscribed oval mass in the infraspinatus muscle. Case 3 A 48-year-old white female noted a painless left gluteal mass for 1 year, which grew slowly during this period. Clinical examination revealed a 3 cm x 5 cm, non-tender, deeply seated left gluteal mass. There was 485
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Figure 1. MRI of the left shoulder, (a) Axial 7,-weighted image (TR 400/TE 20) and (b) axial r r weighted image (TR 2000/TE 80). MRI reveals an oval, sharply defined lesion in the left deltoid muscle with hypointense signal on the r,-weighted image and bright signal on the r2-weighted image. Both signals are homogeneous.
no neurovascular deficit. MRI revealed an oval mass in the left gluteus maximus (Fig. 2). Case 4 A 38-year-old black female noted 3 months earlier a painless, deeply seated mass in the proximal part of the right thigh. Physical examination revealed full range of movement of the right hip and knee without neurological deficit. A firm, mobile, non-tender mass, 4 cm x 8 cm, was felt in the proximal anteromedial part of the right thigh. MRI showed the mass to be in the vastus medialis (Fig. 3). Case 5 A 65-year-old Asian male presented with a 6-month history of a firm, painless mass on the medial aspect of
the left thigh. Physical examination revealed an oval, non-tender mass approximately 4 cm x 5 cm in its greatest diameter located in the mid-thigh in the region of the adductor muscles. The overlying skin and the neuro vascular bundle were intact. MRI revealed the mass to be in the semimembranosus muscle (Fig. 4). Case 6 A 36-year-old white male presented with a mass in the anterolateral aspect of the left knee just proximal to the patella, noticed 1 year earlier. Lately the mass became painful during walking and climbing stairs. A laminectomy had been performed 12 years earlier. Physical examination revealed a firm nodule on the lateral aspect of the quadriceps tendon approximately 3 cm proximal to the patella. The mass was mobile and slightly tender
Figure 2. MRI of the left buttock, (a) Axial 7>weighted image (TR 570/TE 20) and (b) axial 7>weighted image (TR 2000/TE 85). MRI demonstrates an oval, sharply defined mass in the left gluteus maximus, which has a low signal intensity on the T,-weighted image and high signal intensity on the T2-weighted image with homogeneity in both signals.
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Figure 3. MRI of the right thigh, (a) Coronal r,-weighted image (TR 600/TE 20) and (b) axial r r weighted image (TR 2000/TE 60). MRI shows an oval lesion that has sharp borders in the vastus medialis muscle with homogeneous hypointense signal on the Tx -weighted image and homogeneous bright signal on the T2- weigh ted image.
on deep palpation. It was attached neither to the skin nor to the bone. There was a full range of movement in the hip and knee. MRI revealed the mass to be in the quadriceps muscle. Discussion Although the superiority of MRI over CT in evaluating soft-tissue masses is well established, the specificity of MRI in the histological diagnosis of these tumours is less than 20% (Kransdorf et al, 1989a). Tumours with substantial amounts of myxoid tissue may be benign as intramuscular myxomas or they may Vol. 65, No. 774
be malignant tumours undergoing myxomatous degeneration. The majority of intramuscular myxomas occur between the fourth and seventh decades They are less commonly encountered in young adults and rarely in children (Ireland et al, 1973; Canalis et al, 1976; Kransdorf et al, 1989b). The mean age in our cases was 49 years. There is a slight female predominance (Canalis et al, 1976); four of our six patients were women. The most common site of myxoma is the heart (Stout, 1948). If we eliminate bony myxomas, which are almost exclusively in the jaws with only a few cases reported in the long tubular bones and pelvis (Stout, 1948; Ireland et al, 1973; Canalis et al, 1976; McClure & Dahlin, 1977; Abdelwahab et al, 1991), the majority of extracardiac soft-tissue myxomas occur in the musculature of the extremities, particularly of the thigh and shoulder girdle (Stout, 1948; Enzinger, 1965; Ireland et al, 1973). Three of our cases occurred in the thigh and two in the shoulder. To date, the total number of intramuscular myxomas is less than 150 (Canalis et al, 1976; McCook et al, 1981). The tumour usually presents as a painless mass. About 20% of patients are symptomatic, complaining of pain and/or tenderness (Enzinger, 1965). The rate of tumour growth is variable, and occasionally there is no apparent growth over long periods of time (Kransdorf et al, 1989b). It is rare for the tumour to be clinically diagnosed before MRI or biopsy. There has been no documented case of metastasis (Shugar et al, 1987). In 1948, Stout defined the myxoma as a true mesenchymal neoplasm composed of undifferentiated stellate cells in myxoid stroma. Enzinger (1965), reviewing softtissue myxomas but excluding cardiac myxomas, found that one of every six myxomas was located in muscle. On gross inspection, the tumour is oval or spherical in shape, and when cut open presents a white or grey-white mucoid, gelatinous surface. Small cyst-like spaces or traversing trabeculae are not uncommon. On close inspection, the delicate fibrous capsule is usually incomplete and practically all lesions infiltrate adjacent muscles. Microscopically, myxoma is composed of stellate cells and a meshwork of reticulum fibres in a matrix of mucoid material that contains hyaluronic acid (Stout, 1948; Kindbloom et al, 1974) (Fig. 5). Although Stout stated that the recurrence rate was high after resection of these tumours, other reports, including ours, have not confirmed this (Enzinger, 1965; Kindbloom et al, 1974; Feldman, 1979). There is an association between intramuscular myxomas and fibrous dysplasia (Ireland et al, 1973; Sundaram et al, 1989). Wirth et al (1971) described this association as a syndrome in which intramuscular myxomas are an extraskeletal manifestation of fibrous dysplasia. The majority of tumours are associated with polyostotic fibrous dysplasia (Wirth et al, 1971; Logel, 1976; Dahlin, 1987). The intramuscular myxomas are usually located in the vicinity of the most severely affected bones and most often occur in the thigh and may be multiple. Half of the patients had some manifestation of Albright's syndrome (Logel, 487
/. F. Abdelwahab, S. Kenan, G. Hermann, M. M. Lewis and M. J. Klein
Figure 4. MRI of the left thigh, (a) Axial T.-weighted image (TR 500/TE 30) and (b) axial J2-weighted image (TR 2000/TE 60). MRI reveals an oval lesion with sharp borders in the semimembranosus muscle, which has low signal intensity on the r r weighted image and high signal intensity on the r r weighted image. Both signals are uniform.
1976). To date, there are less than 20 cases of intramuscular myxomas associated with fibrous dysplasia. Of these, only two cases were associated with monostotic fibrous dysplasia (Ireland et al, 1973; Sundaram et al, 1989). The possibility of associated fibrous dysplasia when an intramuscular myxoma is discovered should always be considered. Our six cases were not associated with fibrous dysplasia. Intramuscular myxomas are rare tumours. In three large series of soft-tissue tumours studied by MRI, totalling 258, there were only three intramuscular myxomas (Sundaram et al, 1988; Kransdorf et al, 1989a; Berquist et al, 1990). There are also sporadic case
reports of intramuscular myxomas in which MRI was performed (Kransdorf et al, 1989b; Sundaram et al, 1989). Our series of six intramuscular myxomas seems to be the largest studied by MRI. The characteristic pattern of MRI was typical in all our cases. However, our experience differed from other authors. In a recent report by Peterson et al (1991), although three of their four cases of intramuscular myxomas demonstrated the typical MRI characteristics, one case that was homogeneous on both Tx- and T2weighted images demonstrated, only after contrast enhancement, an irregular contrast enhancement in only one of the two components of the lesion. Part of the
(a) Figure 5. Photomicrographs, (a) A low-power view demonstrating loose textured, avascular myxoid tissue of the tumour (left and centre). A fibrous capsule separates the lesion from the skeletal muscle fibres (right) ( x 11). (b) A high-power view reveals spindle and stellate cells with long processes in a loose acellular myxoid stroma ( x 113).
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Intramuscular myxoma: magnetic resonance features
Figure 6. MRI of the right leg. (a) Coronal r,-weighted image (TE 400/TE 20) and (b) axial T2-weighted image (TR 1800/TE 60). The coronal slice reveals an oval, sharply defined lesion in the proximal part of the right leg with low signal intensity. Note the stalk between the lesion and the superior tibiofibular joint. The signal is bright on the r2-weighted image. The above appearances are characteristic of an intramuscular ganglion.
border was also not sharply denned. In one of two cases of intramuscular myxomas reported by Kransdorf et al (1989b), MRI revealed on 7> and T2-weighted pulse sequences an area of increased signal intensity in the distal aspect of the tumour similar to subcutaneous fat. As fluid and myxoid tissue have the same MRI characteristics, our diagnosis was incorrect in three rare benign lesions that contained mainly fluid. Two were intramuscular ganglia in the proximal part of the leg, which communicated with the synovium of the knee joint by a thin duct-like structure lined by single, flattened endothelial cells. Retrospective study of the MRI of the intramuscular ganglia revealed, in the cuts performed in the coronal plane, the tract between the ganglion and the knee joint (Fig. 6). We, therefore, emphasize performing MRI in the coronal planes, particularly when fluid-containing lesions are close to the joints. The third lesion was an intramuscular cysticercus cellulose located in the brachioradialis muscle of the right forearm in a Middle Eastern young male. The lesion contained gelatinous fluid. Acute haematoma containing fresh blood can mimic myxoma, although there is usually a history of trauma with a Vol. 65, No. 774
painful tender swelling. Intramuscular abscess usually has inhomogeneous signal intensity, depending on the amount of protein and necrotic debris within the abscess, with oedema in the surrounding tissue. Schwannomas are attached to the nerve roots outside the muscles, but if large, may compress the surrounding muscles and may simulate myxoma. However, they are usually more hyperintense than the muscle on r,-weighted images and have areas of decreased signal intensity on r2-weighted images. Some malignant softtissue tumours, namely liposarcomas, chondrosarcoma and malignant fibrous histiocytomas, may undergo myxomatous degeneration and may demonstrate a high signal intensity on T2-weighted images, simulting intramuscular myxomas. However, these tumours usually lack the uniformity of the signal intensity and usually have septations on r2-weighted images (Kransdorf et al, 1989a; London et al, 1989). Myxoid liposarcomas constitute approximately 50% of liposarcomas. They show amorphous or linear foci of high signal within a low signal mass on Trweighted images and one should consider this possibility even if the tumour otherwise appears benign (Sundaram et al, 1990). Occasionally, a 489
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malignant tumour may have a homogeneous signal intensity with a sharply defined margin. A signal intensity on a r,-weighted image greater than muscle or if the tumour is extramuscular, may differentiate them from myxomas. We conclude that MRI characteristics of intramuscular myxomas are typical in the majority of cases and that benign lesions which contain mainlyfluidmay mimic intramuscular myxomas. On the other hand, malignant soft-tissue tumours with myxomatous degeneration can be differentiated by the heterogeneity of the signal intensity on both T{- and T2- weigh ted images and the presence of septations. Acknowledgments The authors wish to thank Thomas A. Einhorn, MD, for Case 1 and Herbert S. Sherry, MD, for Case 3. References ABDELWAHAB, I. F., HERMANN, G., KLEIN, M. J., KENAN, S. &
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