- Email: [email protected]
Enveloping of periosteum on the hamstring tendon graft in anterior cruciate ligament reconstruction
Case Report
A True Intra-articular Lipoma of the Knee in a Girl Takashi Marui, M.D., Tetsuji Yamamoto, M.D., Takuya Kimura, M.D., Toshihiro Akisue, M.D., Keiko Nagira, M.D., Tetsuya Nakatani, M.D., Toshiaki Hitora, M.D., and Masahiro Kurosaka, M.D.
Abstract: A 16-year-old girl presented with a soft-tissue mass in the anterolateral aspect of her right knee. Magnetic resonance imaging revealed an intra-articular tumor arising from the anterior fat pad of the knee. The tumor showed low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. It was resected under arthroscopic guidance. Grossly, the tumor was composed of soft, yellowish adipose tissue. Pathologic examination revealed a collection of mature adipocytes with marked myxoid changes in the matrix. A diagnosis of lipoma was made. True intra-articular lipomas should be distinguished from lipoma arborescens, which is considered to be a reactive process. In the English language literature, we found only 7 cases of true intra-articular lipoma reported previously. The present case is the youngest patient with such a tumor, and all the previous reports are of the tumor in adult patients. Intra-articular lipoma should be considered in the differential diagnosis of intra-articular masses in adolescents. Key Words: Lipoma—Magnetic resonance imaging—Arthroscopy—Knee joint—Adolescent.
A
lthough lipomas are the most common benign neoplasms of the soft tissues, they rarely occur within articular components.1 Lipoma arborescens is a well-established clinicopathologic entity that occurs in joints. However, lipoma arborescens is currently recognized as a reactive process secondary to degenerative joint disease and not as a neoplasm. True intraarticular lipoma is encountered extremely rarely and should be distinguished from lipoma arborescens. Although most true intra-articular lipomas have been reported to occur in adults,2-8 we describe a case of
From the Department of Orthopaedic Surgery, Kobe University School of Medicine; and the Department of Orthopaedic Surgery, Hyogo Nojigiku Medical Center for Disabled Children (T.K.), Kobe, Japan. Address reprint requests to Takashi Marui, M.D., Department of Orthopaedic Surgery, Kobe University School of Medicine, 7-5-1 Kusunoki-cho Chuo-ku, Kobe 650-0017 Japan. E-mail: tmarui@ med.kobe-u.ac.jp. © 2002 by the Arthroscopy Association of North America 1526-3231/02/1805-3100$35.00/0 doi:10.1053/jars.2002.29935
true intra-articular lipoma occurring in the knee joint of a young girl.
CASE REPORT A 16-year-old girl presented with right knee pain of approximately 3 months’ duration. She had no history of injury to the knee. Physical examination revealed a palpable mass, measuring 1.5 cm in diameter, located in the anterolateral aspect of the right knee. The mass was round, smooth surfaced, soft, well defined, and mildly tender. It disappeared on flexion of the knee. The range of motion of the knee was not limited. No hydroarthrosis or synovial swelling was noted. Routine laboratory examinations were normal. Routine roentgenograms of the right knee revealed a radiolucent area with fat attenuation in the anterolateral aspect of the knee. Magnetic resonance imaging (MRI) revealed a tumor posterior to the fat pad protruding into the lateral joint space. The tumor exhibited low signal intensity on T1-weighted images (Fig 1A) and greater signal intensity than that of
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 5 (May-June), 2002: E24
1
2
T. MARUI ET AL.
FIGURE 1. MRI of the right knee showed an intra-articular mass arising from the anterior fat pad. The lesion shows low signal intensity on (A) T1-weighted images (repetition time, 500 msec; echo time, 16 msec) and high signal intensity on (B) T2-weighted images (repetition time, 4,000 msec; echo time, 108 msec). Hypointense, thin, wispy septa are seen within the lesion on the T2-weighted images (arrow head).
subcutaneous fat on T2-weighted images. Thin, wispy, hypointense septal structures within the lesion were observed on T2-weighted images (Fig 1B). The patient subsequently underwent arthroscopic examination, which revealed a yellowish, encapsulated mass arising from the anterior fat pad. The mass protruded posteriorly into the lateral joint space. No associated damage of the joint structures, including menisci or the cruciate ligaments, was observed. The tumor was totally excised under arthroscopic guidance. Grossly, the excised mass, measuring 4 ⫻ 3 ⫻ 3 cm, was composed of yellowish adipose tissue and covered by a fibrous capsule (Fig 2). Histologic examination of the specimen revealed a tumor consisting of mature fat cells varying little in size and shape (Fig 3). An abundance of mucoid materials and a few chronic inflammatory cells were seen in the intercellular space. No lipoblasts or atypical cells were found. Mitotic figures were absent. A pathologic diagnosis of
FIGURE 2. Gross appearance of the resected specimen. The tumor consists of yellowish adipose tissue covered with a thin fibrous capsule.
INTRA-ARTICULAR LIPOMA
FIGURE 3. Microscopic appearance of intra-articular lipoma. The tumor consists of mature fat cells with no atypical nuclei. Mucoid degeneration of the matrix and inflammatory cell infiltration are seen in the intercellular space, as are thin fibrous septa between lobules of adipocytes.
lipoma was made. The postoperative course was uneventful. The patient was asymptomatic, and there was no tumor recurrence at follow-up 6 months postoperatively. DISCUSSION True intra-articular lipoma should be distinguished from lipoma arborescens, which is a more common form of intra-articular fat proliferation.4,5,8 Lipoma arborescens represents a coarsely villous, polypoid synovial proliferation, which may be circumscribed or diffused.4,9 It usually appears in response to chronic irritation of the synovial membrane.4 On the other hand, true intra-articular lipoma is a solitary, round to oval mass composed of mature adipose tissue covered by a thin fibrous capsule just like its soft-tissue counterpart.5 Intra-articular lipomas are usually small, may have a short stalk, and are apparently neoplastic.4,5 In our case, the tumor was a solitary mass of adipose tissue projecting from the fat pad, the gross appearance of which was compatible with that of a true intra-articular lipoma. Lipoma arborescens occurs in association with degenerative joint disease, but true intra-articular lipoma occurs de novo. Our patient had no previous knee joint disease. She was not an active athlete, and furthermore, she had no history of antecedent trauma of the leg or the affected knee. These clinical features and gross findings of the tumor suggest that our patient had a true intra-articular lipoma.
3
The differential diagnosis of intra-articular lipoma includes Hoffa disease. In 1904, Hoffa10 first described an inflammatory condition resulting from impingement of the infrapatellar fat pad. Hoffa disease is characterized by hypertrophy of the infrapatellar fat pad caused by post-traumatic hemorrhage and subsequent fibrosis.10-14 The enlarged fat pad usually protrudes from the synovial membrane into the joint,14 sometimes resembling a tumor. In Hoffa disease, fibrin and hemosiderin exhibiting low signal intensity are usually observed on both T1- and T2-weighted MRI.15 Histologically, the lesion is covered by hypertrophic synovium showing chronic inflammatory changes.13 In our case, hypointense septal structures within the lesion, a characteristic of lipoma, were observed on T1-weighted MRI.16,17 In addition, histologically the lesion lacked synovial lining on its surface. Intra-articular lipoma is extremely rare. In the English language literature, we found only 7 cases reported (Table 1) including 5 in the knee joint,2,4,5,7,8 1 in the hip joint,6 and 1 in the lumbar spine.3 However, the exact incidence of true intra-articular lipomas is unclear because several authors seem to confuse intraarticular lipomas with lipoma arborescens.8 Subsequent to the report by Smillie,7 only 2 of the 7 articles clearly describe the neoplastic nature of true intraarticular lipomas as different from lipoma arborescens.5,8 Others argue that the origin of the condition is mechanical3,6 or metabolic.2 Several authors argue that their cases were of true lipomas in the light of the absence of trauma; joint disorders; or associated osteochondral, ligamentous, or meniscal disorders. However, all previously reported cases occurred in TABLE 1. Previous Reports of True Intra-articular Lipoma Authors
Age/Gender
Affected Joint
Antecedent Trauma or Joint Disorders
Jaffe4 Smillie7 Pudlowski et al.5
52/Female 56/Female 53/Male
Knee Knee Knee
Unknown Unknown Medial meniscus tear and cartilage erosion None
Husson et al.3
47/Male
Hill et al.2 Margheritini et al.6 Matsumoto et al.8 Our case
53/Male 31/Male
Lumbar facet Knee Hip
73/Female
Knee
None
16/Female
Knee
None
Chondromalacia Labral tear
4
T. MARUI ET AL.
adult patients, ranging in age from 31 to 73 years of age. Our patient is the youngest patient reported so far with intra-articular lipoma suggestive of the neoplastic nature of the disease. The MRI findings in the current case were atypical. Although classic lipomas show a high signal intensity on T1-weighted sequences that diminishes as T2weighting is augmented,17 the tumor in our case was hypointense on T1-weighted images and hyperintense on T2-weighted images. Matsumoto et al.8 were the first to report the features on MRI of a true intraarticular lipoma. They showed that the intra-articular lipoma shows a high signal intensity with linear structures of low signal intensity on T1-weighted and T2weighted images. The difference in the signal intensity on T1-weighted images is explained by the histologic extent of mucoid degeneration in the tumor. Intra-articular lipomas are subject to mechanical stresses because of interposition of the tumor mass between the articular surface or strangulation of the tumor secondary to volvulus about its stalk.4,5 The degenerative changes in the tumors can be interpreted as being the result of mechanical stresses on the tumor. In summary, a very rare case of true intra-articular lipoma in the knee joint of an adolescent patient is reported. The occurrence of an intra-articular lipoma in an adolescent has never been reported to date. Intra-articular lipoma should be considered in the differential diagnosis when evaluating young patients with knee pain. REFERENCES 1. Lichtenstein L. Bone tumors Ed 2. St. Louis: Mosby, 1959; 387-388.
2. Hill JA, Martin WD, Milgram JW. Unusual arthroscopic knee lesions: Case report of an intra-articular lipoma. J Natl Med Assoc 1993;85:697-699. 3. Husson JL, Chales G, Lancien G, Pawlotsky Y, Masse A. True intra-articular lipoma of the lumbar spine. Spine 1987;12:820822. 4. Jaffe HL. Lipoma and fibroma of articular capsules. In: Jaffe HL, ed. Tumor and tumorous conditions of the bone and joints. Philadelphia: Lea & Febiger, 1958;574-575. 5. Pudlowski RM, Gilula LA, Kyriakos M. Intraarticular lipoma with osseous metaplasia: Radiologic-pathologic correlation. AJR Am J Roentgenol 1979;132:471-473. 6. Margheritini F, Villar RN, Rees D. Intra-articular lipoma of the hip. A case report. Int Orthop 1998;22:328-329. 7. Smillie IS. Disease of the knee joint. Edinburgh: Churchill Livingstone, 1974;411. 8. Matsumoto K, Okabe M, Ishizawa M, Hiraoka S. Intra-articular lipoma of the knee joint—A case report. J Bone Joint Surg Am 2001;83:101-105. 9. Kloen P, Keel SB, Chandler HP, Geiger RH, Zarins B, Rosenberg AE. Lipoma arborescens of the knee. J Bone Joint Surg Br 1998;80:298-301. 10. Hoffa A. Influence of adipose tissue with regard to the pathology of the knee joint. JAMA 1904;43:795-796. 11. Krebs VE, Parker RD. Arthroscopic resection of an extrasynovial ossifying chondroma of the infrapatellar fat pad: endstage Hoffa’s disease? Arthroscopy 1994;10:301-304. 12. Metheny JA, Mayor MB. Hoffa disease: Chronic impingement of the infra-patellar fat pad. Am J Knee Surg 1988;1: 134-139. 13. Ogilvie-Harris DJ, Giddens J. Hoffa’s disease: Arthroscopic resection of the infrapatellar fat pad. Arthroscopy 1994;10: 184-187. 14. Smillie IS. Lesions of the infrapatellar fat pad and synovial fringes: Hoffa’s disease. Acta Orthop Scand 1963;33:371373. 15. Jacobson JA, Lenchik L, Ruhoy MK, Schweitzer ME, Resnick D. MR imaging of the infrapatellar fat pad of Hoffa. Radiographics 1997;17:675-91. 16. Matsumoto K, Hukuda S, Ishizawa M, Chano T, Okabe H. MRI findings in intramuscular lipomas. Skel Radiol 1999;28: 145-152. 17. Munk PL, Lee MJ, Janzen DL, et al. Lipoma and liposarcoma: evaluation using CT and MR imaging. AJR Am J Roentgenol 1997;169:589-594.
A True Intra-articular Lipoma of the Knee in a Girl Takashi Marui, M.D., Tetsuji Yamamoto, M.D., Takuya Kimura, M.D., Toshihiro Akisue, M.D., Keiko Nagira, M.D., Tetsuya Nakatani, M.D., Toshiaki Hitora, M.D., and Masahiro Kurosaka, M.D.
Abstract: A 16-year-old girl presented with a soft-tissue mass in the anterolateral aspect of her right knee. Magnetic resonance imaging revealed an intra-articular tumor arising from the anterior fat pad of the knee. The tumor showed low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. It was resected under arthroscopic guidance. Grossly, the tumor was composed of soft, yellowish adipose tissue. Pathologic examination revealed a collection of mature adipocytes with marked myxoid changes in the matrix. A diagnosis of lipoma was made. True intra-articular lipomas should be distinguished from lipoma arborescens, which is considered to be a reactive process. In the English language literature, we found only 7 cases of true intra-articular lipoma reported previously. The present case is the youngest patient with such a tumor, and all the previous reports are of the tumor in adult patients. Intra-articular lipoma should be considered in the differential diagnosis of intra-articular masses in adolescents. Key Words: Lipoma—Magnetic resonance imaging—Arthroscopy—Knee joint—Adolescent.
A
lthough lipomas are the most common benign neoplasms of the soft tissues, they rarely occur within articular components.1 Lipoma arborescens is a well-established clinicopathologic entity that occurs in joints. However, lipoma arborescens is currently recognized as a reactive process secondary to degenerative joint disease and not as a neoplasm. True intraarticular lipoma is encountered extremely rarely and should be distinguished from lipoma arborescens. Although most true intra-articular lipomas have been reported to occur in adults,2-8 we describe a case of
From the Department of Orthopaedic Surgery, Kobe University School of Medicine; and the Department of Orthopaedic Surgery, Hyogo Nojigiku Medical Center for Disabled Children (T.K.), Kobe, Japan. Address reprint requests to Takashi Marui, M.D., Department of Orthopaedic Surgery, Kobe University School of Medicine, 7-5-1 Kusunoki-cho Chuo-ku, Kobe 650-0017 Japan. E-mail: tmarui@ med.kobe-u.ac.jp. © 2002 by the Arthroscopy Association of North America 1526-3231/02/1805-3100$35.00/0 doi:10.1053/jars.2002.29935
true intra-articular lipoma occurring in the knee joint of a young girl.
CASE REPORT A 16-year-old girl presented with right knee pain of approximately 3 months’ duration. She had no history of injury to the knee. Physical examination revealed a palpable mass, measuring 1.5 cm in diameter, located in the anterolateral aspect of the right knee. The mass was round, smooth surfaced, soft, well defined, and mildly tender. It disappeared on flexion of the knee. The range of motion of the knee was not limited. No hydroarthrosis or synovial swelling was noted. Routine laboratory examinations were normal. Routine roentgenograms of the right knee revealed a radiolucent area with fat attenuation in the anterolateral aspect of the knee. Magnetic resonance imaging (MRI) revealed a tumor posterior to the fat pad protruding into the lateral joint space. The tumor exhibited low signal intensity on T1-weighted images (Fig 1A) and greater signal intensity than that of
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 5 (May-June), 2002: E24
1
2
T. MARUI ET AL.
FIGURE 1. MRI of the right knee showed an intra-articular mass arising from the anterior fat pad. The lesion shows low signal intensity on (A) T1-weighted images (repetition time, 500 msec; echo time, 16 msec) and high signal intensity on (B) T2-weighted images (repetition time, 4,000 msec; echo time, 108 msec). Hypointense, thin, wispy septa are seen within the lesion on the T2-weighted images (arrow head).
subcutaneous fat on T2-weighted images. Thin, wispy, hypointense septal structures within the lesion were observed on T2-weighted images (Fig 1B). The patient subsequently underwent arthroscopic examination, which revealed a yellowish, encapsulated mass arising from the anterior fat pad. The mass protruded posteriorly into the lateral joint space. No associated damage of the joint structures, including menisci or the cruciate ligaments, was observed. The tumor was totally excised under arthroscopic guidance. Grossly, the excised mass, measuring 4 ⫻ 3 ⫻ 3 cm, was composed of yellowish adipose tissue and covered by a fibrous capsule (Fig 2). Histologic examination of the specimen revealed a tumor consisting of mature fat cells varying little in size and shape (Fig 3). An abundance of mucoid materials and a few chronic inflammatory cells were seen in the intercellular space. No lipoblasts or atypical cells were found. Mitotic figures were absent. A pathologic diagnosis of
FIGURE 2. Gross appearance of the resected specimen. The tumor consists of yellowish adipose tissue covered with a thin fibrous capsule.
INTRA-ARTICULAR LIPOMA
FIGURE 3. Microscopic appearance of intra-articular lipoma. The tumor consists of mature fat cells with no atypical nuclei. Mucoid degeneration of the matrix and inflammatory cell infiltration are seen in the intercellular space, as are thin fibrous septa between lobules of adipocytes.
lipoma was made. The postoperative course was uneventful. The patient was asymptomatic, and there was no tumor recurrence at follow-up 6 months postoperatively. DISCUSSION True intra-articular lipoma should be distinguished from lipoma arborescens, which is a more common form of intra-articular fat proliferation.4,5,8 Lipoma arborescens represents a coarsely villous, polypoid synovial proliferation, which may be circumscribed or diffused.4,9 It usually appears in response to chronic irritation of the synovial membrane.4 On the other hand, true intra-articular lipoma is a solitary, round to oval mass composed of mature adipose tissue covered by a thin fibrous capsule just like its soft-tissue counterpart.5 Intra-articular lipomas are usually small, may have a short stalk, and are apparently neoplastic.4,5 In our case, the tumor was a solitary mass of adipose tissue projecting from the fat pad, the gross appearance of which was compatible with that of a true intra-articular lipoma. Lipoma arborescens occurs in association with degenerative joint disease, but true intra-articular lipoma occurs de novo. Our patient had no previous knee joint disease. She was not an active athlete, and furthermore, she had no history of antecedent trauma of the leg or the affected knee. These clinical features and gross findings of the tumor suggest that our patient had a true intra-articular lipoma.
3
The differential diagnosis of intra-articular lipoma includes Hoffa disease. In 1904, Hoffa10 first described an inflammatory condition resulting from impingement of the infrapatellar fat pad. Hoffa disease is characterized by hypertrophy of the infrapatellar fat pad caused by post-traumatic hemorrhage and subsequent fibrosis.10-14 The enlarged fat pad usually protrudes from the synovial membrane into the joint,14 sometimes resembling a tumor. In Hoffa disease, fibrin and hemosiderin exhibiting low signal intensity are usually observed on both T1- and T2-weighted MRI.15 Histologically, the lesion is covered by hypertrophic synovium showing chronic inflammatory changes.13 In our case, hypointense septal structures within the lesion, a characteristic of lipoma, were observed on T1-weighted MRI.16,17 In addition, histologically the lesion lacked synovial lining on its surface. Intra-articular lipoma is extremely rare. In the English language literature, we found only 7 cases reported (Table 1) including 5 in the knee joint,2,4,5,7,8 1 in the hip joint,6 and 1 in the lumbar spine.3 However, the exact incidence of true intra-articular lipomas is unclear because several authors seem to confuse intraarticular lipomas with lipoma arborescens.8 Subsequent to the report by Smillie,7 only 2 of the 7 articles clearly describe the neoplastic nature of true intraarticular lipomas as different from lipoma arborescens.5,8 Others argue that the origin of the condition is mechanical3,6 or metabolic.2 Several authors argue that their cases were of true lipomas in the light of the absence of trauma; joint disorders; or associated osteochondral, ligamentous, or meniscal disorders. However, all previously reported cases occurred in TABLE 1. Previous Reports of True Intra-articular Lipoma Authors
Age/Gender
Affected Joint
Antecedent Trauma or Joint Disorders
Jaffe4 Smillie7 Pudlowski et al.5
52/Female 56/Female 53/Male
Knee Knee Knee
Unknown Unknown Medial meniscus tear and cartilage erosion None
Husson et al.3
47/Male
Hill et al.2 Margheritini et al.6 Matsumoto et al.8 Our case
53/Male 31/Male
Lumbar facet Knee Hip
73/Female
Knee
None
16/Female
Knee
None
Chondromalacia Labral tear
4
T. MARUI ET AL.
adult patients, ranging in age from 31 to 73 years of age. Our patient is the youngest patient reported so far with intra-articular lipoma suggestive of the neoplastic nature of the disease. The MRI findings in the current case were atypical. Although classic lipomas show a high signal intensity on T1-weighted sequences that diminishes as T2weighting is augmented,17 the tumor in our case was hypointense on T1-weighted images and hyperintense on T2-weighted images. Matsumoto et al.8 were the first to report the features on MRI of a true intraarticular lipoma. They showed that the intra-articular lipoma shows a high signal intensity with linear structures of low signal intensity on T1-weighted and T2weighted images. The difference in the signal intensity on T1-weighted images is explained by the histologic extent of mucoid degeneration in the tumor. Intra-articular lipomas are subject to mechanical stresses because of interposition of the tumor mass between the articular surface or strangulation of the tumor secondary to volvulus about its stalk.4,5 The degenerative changes in the tumors can be interpreted as being the result of mechanical stresses on the tumor. In summary, a very rare case of true intra-articular lipoma in the knee joint of an adolescent patient is reported. The occurrence of an intra-articular lipoma in an adolescent has never been reported to date. Intra-articular lipoma should be considered in the differential diagnosis when evaluating young patients with knee pain. REFERENCES 1. Lichtenstein L. Bone tumors Ed 2. St. Louis: Mosby, 1959; 387-388.
2. Hill JA, Martin WD, Milgram JW. Unusual arthroscopic knee lesions: Case report of an intra-articular lipoma. J Natl Med Assoc 1993;85:697-699. 3. Husson JL, Chales G, Lancien G, Pawlotsky Y, Masse A. True intra-articular lipoma of the lumbar spine. Spine 1987;12:820822. 4. Jaffe HL. Lipoma and fibroma of articular capsules. In: Jaffe HL, ed. Tumor and tumorous conditions of the bone and joints. Philadelphia: Lea & Febiger, 1958;574-575. 5. Pudlowski RM, Gilula LA, Kyriakos M. Intraarticular lipoma with osseous metaplasia: Radiologic-pathologic correlation. AJR Am J Roentgenol 1979;132:471-473. 6. Margheritini F, Villar RN, Rees D. Intra-articular lipoma of the hip. A case report. Int Orthop 1998;22:328-329. 7. Smillie IS. Disease of the knee joint. Edinburgh: Churchill Livingstone, 1974;411. 8. Matsumoto K, Okabe M, Ishizawa M, Hiraoka S. Intra-articular lipoma of the knee joint—A case report. J Bone Joint Surg Am 2001;83:101-105. 9. Kloen P, Keel SB, Chandler HP, Geiger RH, Zarins B, Rosenberg AE. Lipoma arborescens of the knee. J Bone Joint Surg Br 1998;80:298-301. 10. Hoffa A. Influence of adipose tissue with regard to the pathology of the knee joint. JAMA 1904;43:795-796. 11. Krebs VE, Parker RD. Arthroscopic resection of an extrasynovial ossifying chondroma of the infrapatellar fat pad: endstage Hoffa’s disease? Arthroscopy 1994;10:301-304. 12. Metheny JA, Mayor MB. Hoffa disease: Chronic impingement of the infra-patellar fat pad. Am J Knee Surg 1988;1: 134-139. 13. Ogilvie-Harris DJ, Giddens J. Hoffa’s disease: Arthroscopic resection of the infrapatellar fat pad. Arthroscopy 1994;10: 184-187. 14. Smillie IS. Lesions of the infrapatellar fat pad and synovial fringes: Hoffa’s disease. Acta Orthop Scand 1963;33:371373. 15. Jacobson JA, Lenchik L, Ruhoy MK, Schweitzer ME, Resnick D. MR imaging of the infrapatellar fat pad of Hoffa. Radiographics 1997;17:675-91. 16. Matsumoto K, Hukuda S, Ishizawa M, Chano T, Okabe H. MRI findings in intramuscular lipomas. Skel Radiol 1999;28: 145-152. 17. Munk PL, Lee MJ, Janzen DL, et al. Lipoma and liposarcoma: evaluation using CT and MR imaging. AJR Am J Roentgenol 1997;169:589-594.