Case report
A 45-year-old Japanese man was referred to us with a few day-history of
a subcutaneous mass in the left shoulder area. The patient had
arrhythmogenic right ventricular cardiomyopathy associated with
arrhythmia after cardioverter-defibrillator implantation and
dyslipidemia. There was no family history of mesenchymal tumors or a
previous history of trauma to the left shoulder area.
A physical examination revealed a 7-cm dome-shaped subcutaneous mass on
the left shoulder with poor mobility to the lower floor (Figure
1a ). Magnetic resonance imaging (MRI) showed a subcutaneous mass
measuring approximately 6.0 × 5.0 × 2.5 cm without findings of invasion
into the deep muscle layer (Figure 1b ). The tumor had a
well-demarcated margin from the surrounding tissue and a heterogeneous
structure with a septum. Fat-suppressed T1-weighted images revealed
fat-suppressed areas, suggesting the presence of a fatty component
(Figure 1c ). Based on these findings, we initially considered
the tumor to be an atypical lipomatous tumor or liposarcoma. Therefore,
we dissected the tumor with a narrow margin for a histopathological
examination. Dissection from the surrounding tissues was relatively
easy. The excised mass was covered with an elastic, soft, and thin
capsule that was yellowish in color and contained hard, whitish nodules.
The histopathological examination showed the lobular proliferation of
mature adipocytes, bundles of collagen fibers, and spindle-shaped cells
(Figure 1d and 1e ). Adipocytes and spindle-shaped cells had
neither atypical nuclei nor mitosis. Immunohistochemical staining
revealed that spindle-shaped cells were positive for CD34 and negative
for S100 protein, MDM2, α-smooth muscle actin (αSMA), cyclin-dependent
kinase 4 (CDK4), signal transducer and activator of transcription 6
(STAT6), and desmin. Less than 5% of tumor cells were positive for
mindbomb E3 ubiquitin protein ligase 1 (MIB1) (Figure 2 ). Based
on these results, the patient was diagnosed with SCL. Twelve months
after surgery, neither recurrence nor postoperative complications have
been observed.