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Mobile submuscular mass resembling a hard-boiled egg: case report
J Orthop Sci (2003) 8:613–615 DOI 10.1007/s00776-003-0681-3
Mobile submuscular mass resembling a hard-boiled egg: case report Tetsuo Hagino1, Ken Ishizuka2, Eiichi Sato2, Hideki Kohno2, and Yoshiki Hamada2 1 2
Department of Orthopaedic Surgery, Kofu National Hospital, 11-35 Tenjin-cho, Kofu 400-8533, Japan Department of Orthopaedic Surgery, Faculty of Medicine, University of Yamanashi, Yamanashi, Japan
Abstract A 68-year-old woman had a rare mobile mass on her back. The mass was similar to encapsulated fat necrosis except for its unusual stalked appearance, large size, and high degree of mobility underneath the anterior serratus muscle on the back. Based on previous descriptions of encapsulated fat necrosis, the clinical presentation of the mass might be regarded as an extreme example of this rare condition. Key words Mobile submuscular mass · Encapsulated fat necrosis · Lipoma
Introduction We present a case in which the patient had a large mobile mass on her back. The mass exhibited a pathological appearance similar to encapsulated fat necrosis1 and had the clinical features of a lipoma but with unusual submuscular mobility. This case is distinct from encapsulated fat necrosis or true lipoma.
Case report At the end of February 2000, a 68-year-old woman experienced an uncomfortable feeling on her left back as she retrieved a chopstick she had dropped on the floor during a meal. She noticed a painless mass at that site, leading her to visit our department on March 3. She had initially been diagnosed in 1977 as suffering from rheumatoid arthritis. She underwent total knee arthroplasty on the right knee in 1993 followed by the left knee in 1997. She had no history of taking oral steroids and no remarkable family history. On physical examination, a 4 ⫻ 3 cm elastic, soft mass without
Offprint requests to: T. Hagino Received: December 24, 2002 / Accepted: April 7, 2003
tenderness was palpable below the left scapula. Ultrasonography showed a relatively well demarcated mass with mixed high and low echoes within it. Computed tomography (CT) on March 21, 2000 revealed a well-delineated low-density mass that seemed to be composed of fat and a small calcified component (Fig. 1). CT with contrast medium exhibited no enhancement of the mass. The mass was diagnosed as a lipoma or liposarcoma, and it was decided that the patient would be followed without intervention. Later, around April 14, a swelling around the mass emerged without any apparent cause, and the mass exhibited mobility from the subscapular area to the flank of the chest that had not been observed on her first visit. Magnetic resonance imaging (MRI) on April 19 revealed a fluid collection indicating a hematoma between the left anterior serratus muscle and the thorax as well as an elliptical mass inside it. The mass exhibited a signal intensity similar to that of subcutaneous fat (Fig. 2). She was admitted to the hospital on May 25, 2000 for surgery. The mass could be moved easily from the back to the flank of the chest by manual manipulation without pain. Laboratory studies on admission revealed that her C-reactive protein (CRP) level was 4.0 mg/dl, the erythrocyte sedimentation rate was 80 mm/h, and her rheumatoid factor was positive, indicating the existence of inflammation associated with rheumatoid arthritis. She was operated on under general anesthesia on May 30, 2000. When a cyst was incised during the surgery, a small amount of serous, yellowish, transparent fluid flowed out, and there was a pedunculated yellowish mass like a hard-boiled egg, 5 ⫻ 4 ⫻ 3 cm, with capsule formation inside the cyst (Fig. 3). Histological examination revealed fibrous proliferation in the fat tissue, with the disappearance of nuclei in fibroblasts and adipocytes (Fig. 4). Finally, the patient was diagnosed with an encapsulated mass originating from a true lipoma that became mobile after degeneration based on the imag-
614
T. Hagino et al.: Mobile submuscular mass
a
Fig. 1. Computed tomography findings (March 21, 2000). A well-demarcated low-density mass that seemed to be composed of fat and a small area of calcification was observed
b Fig. 3. Macroscopic findings. The mass was yellowish, like a hard-boiled egg, with capsule formation (a) and a stalk (arrow) to the cyst (b). C, cyst; *, cut surface. Bar 5 mm
ing data and histological examination. At present, November 2002, she has had no recurrence of the mass, is pain-free, and is without other complaints. a
Discussion
b Fig. 2. a Axial T1-weighted magnetic resonance image (T1W1). b Axial T2-weighted image (T2W1) of the trunk (both April 19, 2000). A well-delineated mass with the same signal intensity as that of fat was observed between the left anterior serratus muscle and the rib. A fluid collection around the mass was thought to be a hematoma
The pathological findings found in this case are similar to those described in several publications1–5 since Schmidt-Hermes and Loskant first reported these lesions as constituting well-circumscribed fat necrosis.6 However, there has been no report of a large mass underneath the muscle on the back as observed in this case. The mass reported here has almost the same pathological findings, but this case originated from a true lipoma and not from fat necrosis, suggesting that it is not the same entity. In addition, none of the previous reports produced imaging data as are presented here. Tanaka et al.7 reported the imaging findings of a mobile calcified nodule in the intrathoracic space as thoracolithiasis, and they suggested that the nodule originated from a lipoma and became mobile in the intrathoracic space after degeneration. On the other hand, Sahl5 had designated such an entity a “mobile encapsulated lipoma.” He noted that the origin of the mobile encapsulated lipoma is still
T. Hagino et al.: Mobile submuscular mass
615
b
a
unknown, and that the nodule was not a true tumor but might have its origins as a nodule of fat that separated from its surrounding adipose tissue and was encapsulated as a foreign body. The nodule becomes disconnected from its blood supply via manipulation by the patient or some other external cause and becomes a mobile body. However, the mass in this study was as large as 5 ⫻ 4 ⫻ 3 cm with a stalk and emerged between the anterior serratus muscle and the chest wall, where there was little fat tissue originally. The mass reported here also became mobile over time and seemed to have a hematoma around it. Therefore, we speculate that an existing lipoma was injured by an unidentified cause and bled, forming a hematoma that was later encapsulated with the necrosis of the lipoma, leading to the appearance of a mobile cyst around the hematoma. In conclusion, we presented a case of an extremely rare mobile mass underneath the muscle on the back.
Fig. 4. Microscopic findings. a A capsule formed around the mass, with fibrous proliferation inside the fat deposit exhibiting the disappearance of nuclei (b). a ⫻10. b ⫻200
References 1. Azad SM, Cherian A, Raine C, et al. Encapsulated fat necrosis: a case of “thigh mouse.” Br J Plast Surg 2001;54:643–5. 2. Hurt MA, Santa Cruz DJ. Nodular-cystic fat necrosis. J Am Acad Dermatol 1989;21:493–8. 3. Kiryu H, Rikihisa W, Furue M. Encapsulated fat necrosis: a clinicopathological study of 8 cases and a literature review. J Cutan Pathol 2000;27:19–23. 4. Przyjemski CJ, Schuster SR. Nodular-cystic fat necrosis. J Pediatr 1977;91:605–7. 5. Sahl WJ Jr. Mobile encapsulated lipomas: formerly called encapsulated angiolipomas. Arch Dermatol 1978;114:1684–6. 6. Schmidt-Hermes HJ, Loskant G. Verkalkte Fettgewebsnekrose der weiblichen Brust. Med Welt 1975;26:1179–80. 7. Tanaka D, Niwatsukino H, Fujiyoshi F, et al. Thoracolithiasis: a mobile calcified nodule in the intrathoracic space: radiographic, CT, and MRI findings. Radiat Med 2002;20:131–3.
Mobile submuscular mass resembling a hard-boiled egg: case report Tetsuo Hagino1, Ken Ishizuka2, Eiichi Sato2, Hideki Kohno2, and Yoshiki Hamada2 1 2
Department of Orthopaedic Surgery, Kofu National Hospital, 11-35 Tenjin-cho, Kofu 400-8533, Japan Department of Orthopaedic Surgery, Faculty of Medicine, University of Yamanashi, Yamanashi, Japan
Abstract A 68-year-old woman had a rare mobile mass on her back. The mass was similar to encapsulated fat necrosis except for its unusual stalked appearance, large size, and high degree of mobility underneath the anterior serratus muscle on the back. Based on previous descriptions of encapsulated fat necrosis, the clinical presentation of the mass might be regarded as an extreme example of this rare condition. Key words Mobile submuscular mass · Encapsulated fat necrosis · Lipoma
Introduction We present a case in which the patient had a large mobile mass on her back. The mass exhibited a pathological appearance similar to encapsulated fat necrosis1 and had the clinical features of a lipoma but with unusual submuscular mobility. This case is distinct from encapsulated fat necrosis or true lipoma.
Case report At the end of February 2000, a 68-year-old woman experienced an uncomfortable feeling on her left back as she retrieved a chopstick she had dropped on the floor during a meal. She noticed a painless mass at that site, leading her to visit our department on March 3. She had initially been diagnosed in 1977 as suffering from rheumatoid arthritis. She underwent total knee arthroplasty on the right knee in 1993 followed by the left knee in 1997. She had no history of taking oral steroids and no remarkable family history. On physical examination, a 4 ⫻ 3 cm elastic, soft mass without
Offprint requests to: T. Hagino Received: December 24, 2002 / Accepted: April 7, 2003
tenderness was palpable below the left scapula. Ultrasonography showed a relatively well demarcated mass with mixed high and low echoes within it. Computed tomography (CT) on March 21, 2000 revealed a well-delineated low-density mass that seemed to be composed of fat and a small calcified component (Fig. 1). CT with contrast medium exhibited no enhancement of the mass. The mass was diagnosed as a lipoma or liposarcoma, and it was decided that the patient would be followed without intervention. Later, around April 14, a swelling around the mass emerged without any apparent cause, and the mass exhibited mobility from the subscapular area to the flank of the chest that had not been observed on her first visit. Magnetic resonance imaging (MRI) on April 19 revealed a fluid collection indicating a hematoma between the left anterior serratus muscle and the thorax as well as an elliptical mass inside it. The mass exhibited a signal intensity similar to that of subcutaneous fat (Fig. 2). She was admitted to the hospital on May 25, 2000 for surgery. The mass could be moved easily from the back to the flank of the chest by manual manipulation without pain. Laboratory studies on admission revealed that her C-reactive protein (CRP) level was 4.0 mg/dl, the erythrocyte sedimentation rate was 80 mm/h, and her rheumatoid factor was positive, indicating the existence of inflammation associated with rheumatoid arthritis. She was operated on under general anesthesia on May 30, 2000. When a cyst was incised during the surgery, a small amount of serous, yellowish, transparent fluid flowed out, and there was a pedunculated yellowish mass like a hard-boiled egg, 5 ⫻ 4 ⫻ 3 cm, with capsule formation inside the cyst (Fig. 3). Histological examination revealed fibrous proliferation in the fat tissue, with the disappearance of nuclei in fibroblasts and adipocytes (Fig. 4). Finally, the patient was diagnosed with an encapsulated mass originating from a true lipoma that became mobile after degeneration based on the imag-
614
T. Hagino et al.: Mobile submuscular mass
a
Fig. 1. Computed tomography findings (March 21, 2000). A well-demarcated low-density mass that seemed to be composed of fat and a small area of calcification was observed
b Fig. 3. Macroscopic findings. The mass was yellowish, like a hard-boiled egg, with capsule formation (a) and a stalk (arrow) to the cyst (b). C, cyst; *, cut surface. Bar 5 mm
ing data and histological examination. At present, November 2002, she has had no recurrence of the mass, is pain-free, and is without other complaints. a
Discussion
b Fig. 2. a Axial T1-weighted magnetic resonance image (T1W1). b Axial T2-weighted image (T2W1) of the trunk (both April 19, 2000). A well-delineated mass with the same signal intensity as that of fat was observed between the left anterior serratus muscle and the rib. A fluid collection around the mass was thought to be a hematoma
The pathological findings found in this case are similar to those described in several publications1–5 since Schmidt-Hermes and Loskant first reported these lesions as constituting well-circumscribed fat necrosis.6 However, there has been no report of a large mass underneath the muscle on the back as observed in this case. The mass reported here has almost the same pathological findings, but this case originated from a true lipoma and not from fat necrosis, suggesting that it is not the same entity. In addition, none of the previous reports produced imaging data as are presented here. Tanaka et al.7 reported the imaging findings of a mobile calcified nodule in the intrathoracic space as thoracolithiasis, and they suggested that the nodule originated from a lipoma and became mobile in the intrathoracic space after degeneration. On the other hand, Sahl5 had designated such an entity a “mobile encapsulated lipoma.” He noted that the origin of the mobile encapsulated lipoma is still
T. Hagino et al.: Mobile submuscular mass
615
b
a
unknown, and that the nodule was not a true tumor but might have its origins as a nodule of fat that separated from its surrounding adipose tissue and was encapsulated as a foreign body. The nodule becomes disconnected from its blood supply via manipulation by the patient or some other external cause and becomes a mobile body. However, the mass in this study was as large as 5 ⫻ 4 ⫻ 3 cm with a stalk and emerged between the anterior serratus muscle and the chest wall, where there was little fat tissue originally. The mass reported here also became mobile over time and seemed to have a hematoma around it. Therefore, we speculate that an existing lipoma was injured by an unidentified cause and bled, forming a hematoma that was later encapsulated with the necrosis of the lipoma, leading to the appearance of a mobile cyst around the hematoma. In conclusion, we presented a case of an extremely rare mobile mass underneath the muscle on the back.
Fig. 4. Microscopic findings. a A capsule formed around the mass, with fibrous proliferation inside the fat deposit exhibiting the disappearance of nuclei (b). a ⫻10. b ⫻200
References 1. Azad SM, Cherian A, Raine C, et al. Encapsulated fat necrosis: a case of “thigh mouse.” Br J Plast Surg 2001;54:643–5. 2. Hurt MA, Santa Cruz DJ. Nodular-cystic fat necrosis. J Am Acad Dermatol 1989;21:493–8. 3. Kiryu H, Rikihisa W, Furue M. Encapsulated fat necrosis: a clinicopathological study of 8 cases and a literature review. J Cutan Pathol 2000;27:19–23. 4. Przyjemski CJ, Schuster SR. Nodular-cystic fat necrosis. J Pediatr 1977;91:605–7. 5. Sahl WJ Jr. Mobile encapsulated lipomas: formerly called encapsulated angiolipomas. Arch Dermatol 1978;114:1684–6. 6. Schmidt-Hermes HJ, Loskant G. Verkalkte Fettgewebsnekrose der weiblichen Brust. Med Welt 1975;26:1179–80. 7. Tanaka D, Niwatsukino H, Fujiyoshi F, et al. Thoracolithiasis: a mobile calcified nodule in the intrathoracic space: radiographic, CT, and MRI findings. Radiat Med 2002;20:131–3.