title: Rhabdomyomatous mesenchymal hamartoma presenting as a big subcutaneous mass on the neck: a case report.
abstract: BACKGROUND
  We describe the location, size, histopathologic aspect and immunohistochemical expression of a rhabdomyomatous mesenchymal hamartoma, with the aim of providing useful information for its correct diagnosis.
  
  
  METHODS
  A 31-year-old Chinese man first presented 2 years previously with a solitary subcutaneous mass on the left side of his neck and under his mastoid process; the mass's size was 2 × 2 cm. The mass increased in the size in the past 2 years. Magnetic resonance imaging revealed a dumbbell shaped and well-outlined highly reflective mass, with its upperpart infiltrating the interspace of the atlanto-occipital joint. The mass was surgically removed. On macroscopic examination, the mass was oblong and partly encapsulated, the size of the mass was 4.9 × 3.5 × 3 cm, and its cut side was grey. On histologic examination, it showed a disordered collection of bundles of mature striated muscle fibres arranged in a haphazard manner and interspersed with adipose tissue, fibrocytes or mesenchymocytes and collagen, and had a myxoid matrix. On immunochemical examination, mature striated muscle was positive for desmin and myoglobin, adipose tissue and nerves were positive for S-100 protein, and fibrocytes or mesenchymocytes and collagen were positive for vimentin and cluster of differentiation 34. A diagnosis of rhabdomyomatous mesenchymal hamartoma was established.
  
  
  CONCLUSIONS
  Rhabdomyomatous mesenchymal hamartoma is a rare dermal or subcutaneous lesion, and we describe its immunohistochemical expression for the first time. This case report provides more information on the microscopic appearance and immunohistochemical expression.
authors.affiliation: Department of Pathology, Uromuqi General Hospital, LanZhou, Military District 830054, China. wyl17@sohu.com.
authors.forename: YuLan
authors.initials: Y
authors.lastname: Wang
authors.forename: HaiHua
authors.initials: H
authors.lastname: Zhao
authors.forename: XinHua
authors.initials: X
authors.lastname: Yue
authors.forename: XinPing
authors.initials: X
authors.lastname: Tang
authors.forename: Li
authors.initials: L
authors.lastname: Ma
authors.forename: Yong
authors.initials: Y
authors.lastname: Fu
authors.forename: PeiYi
authors.initials: P
authors.lastname: Zhang
mesh_terms: D000328:Adult; D018952:Antigens, CD34 / Q000378:metabolism; D006222:Hamartoma / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D008297:Male; D008648:Mesoderm / Q000378:metabolism; D054792:Muscle, Striated / Q000378:metabolism / Q000473:pathology*; D009211:Myoglobin / Q000378:metabolism; D009333:Neck
chemical_list: D018952:Antigens, CD34; D009211:Myoglobin