Pediatr Radiol (2006) 36: 974–976 DOI 10.1007/s00247-006-0227-x CASE REPORT Lindsey Grandbois . Aruna Vade . Jennifer Lim-Dunham . Hytham Al-Masri MRI findings of an intermuscular lipoma in a 2-year-old Received: 29 March 2006 / Accepted: 12 April 2006 / Published online: 3 June 2006 # Springer-Verlag 2006 Abstract We report the MRI findings of a large deep intermuscular lipoma in a 2-year-old child with a painless palpable shoulder mass, and its differentiation from liposarcoma and other soft-tissue masses. To our knowl- edge, the imaging features of deep lipomas in children have not been reported. Keywords Intermuscular . Soft-tissue tumor . Deep lipoma Introduction Lipomas account for almost 50% of all soft-tissue tumors. Most lipomas are subcutaneous [1, 2]. Lipomas involving the deep soft tissues are distinctly uncommon. Deep lipomas can be intramuscular and intermuscular [1–3]. Intramuscular lipomas have been reported to account for 1.8% of all fatty tumors, and intermuscular lipomas account for only 0.3% of fatty tumors [4]. Both intramus- cular and intermuscular lipomas generally occur in the 3rd to 6th decades [2]. They affect, in order of prevalence, the skeletal muscles of the lower extremity, the trunk, the shoulder, and the upper extremity [2]. We report MRI findings of a large deep intermuscular lipoma in a child with a painless palpable shoulder mass. Case report A 2-year-old Hispanic girl with a history of a rapidly growing right shoulder mass presented for a right upper extremity MRI. The mass was not painful and had been present for several months. She had no other associated symptoms. She had no prior imaging or work-up and no significant medical history. A right upper extremity MRI revealed a well-circum- scribed bilobed mass with thin septations in the posterior right shoulder measuring 4.3 cm × 4.5 cm × 3.1 cm. The mass was interposed between the deltoid and infraspinatus muscles and demonstrated high signal intensity on T1-weighted images and intermediate to low signal intensity on T2-weighted fat-saturated images (Fig. 1). The capsule and thin septations enhanced after adminis- tration of intravenous gadolinium (Fig. 1). There was no muscular or bony involvement. This mass was removed in its entirety and was histopathologically proven to be a benign lipoma consisting of mature adipocytes (Fig. 2). Discussion Lipomas are composed of normal adult white adipose tissue and are surrounded by a thin capsule that separates them from surrounding tissue [1–3]. Deep lipomas tend to be larger than superficial lipomas and can microscopically infiltrate the surrounding musculature. Deep lipomas involving the extremities most commonly are intramuscu- lar [2]. Intramuscular lipomas are usually poorly margin- ated and infiltrate adjacent fascial planes. Intermuscular lipomas arise between skeletal muscles and remain in this space only. However, large deep lipomas can be associated with both intramuscular and intermuscular involvement [1, 2]. Deep lipomas tend to be much larger than their superficial counterparts and can displace local structures and limit range of motion in the affected muscle groups [1–3]. Deep lipomas present clinically as a nonspecific mass. They might become more distinct during periods of severe weight loss or muscle contraction [2]. L. Grandbois (*) . A. Vade . J. Lim-Dunham Department of Radiology, Loyola University Medical Center, 2160 S. First Ave., Maywood, IL 60153, USA e-mail: lgrandbois@lumc.edu Tel.: +1-708-2161084 Fax: +1-708-2168394 H. Al-Masri Department of Pathology, Mount Sinai Hospital, Chicago, IL, USA