Presentation
Large mass lateral border of the left upper arm. Present since birth.
Patient Data
Large rounded hypoechoic mass centered in the deltoid muscle. No internal hypervascularity. Single lesion.
Awake MRI.
Confirms that the lesion is solitary, extraosseous and centered in the deltoid muscle. No surrounding edema.
US-guided biopsy
Biphasic appearance of hyalinised myoid nodules and spindle-cells.
SMA positive. Calponin focal staining. CD34 vascular channel staining.
Negative: myogenin, MyoD1, caldesmon, S100, STAT6, AE1/3.
Molecular testing (FISH) shows no USP6 gene rearrangement.
Histology and immunohistochemisty: myofibroma.
Case Discussion
This hard intramuscular lesion was present from birth.
Imaging findings are non-specific. Intramuscular. Generalized lack of vascularity. No surrounding edema.
Biopsy confirmed myofibroma. A decision about clinical review vs. excision is yet to be made.
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