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A 69-year-old woman presented with a poorly defined soft tissue mass of the back in the subscapular region. Resection showed a 10.0 cm fibrous mass that was adherent to the chest wall.
Archive Case and Diagnosis:
This case first appeared as Performance Improvement Program in Surgical Pathology (PIP) 2010, case 08, and is an elastofibroma.
Criteria for Diagnosis and Comments:
Histologically the mass is hypocellular, patternless and contains a mixture of haphazardly arranged collagen bundles, myxoid matrix and elastic fibers. Adipose tissue can be seen within the lesion. The elastic fibers have a characteristic beaded and fragmented appearance. This pattern as well as the enormous number of elastic fibers can be highlighted by an elastic stain. Elastofibroma is immunohistochemically positive for vimentin, and negative for S-100, actin and desmin.
Elastofibroma was first reported in 1961 and usually presents as a painless, slow growing mass. Most cases of elastofibroma are localized to the lower subscapular region, are nonadherent to the overlying skin but often adherent to the posterior chest wall. The scapula may overlie the lesion thereby masking it. Elastofibroma is typically not adherent to the surrounding musculature, but often has irregular margins. This lesion is most often diagnosed in the elderly population, with greater than 90% female predominance. Some patients provided a history of significant manual labor involving the shoulder girdle possibly accounting for the right-sided predominance of this lesion.
The typical appearance of elastofibroma on computed tomographic scan reveals a poorly circumscribed mass which is isodense to surrounding muscle and is often difficult to delineate from surrounding muscle planes. Magnetic resonance imaging will show soft tissue masses with streaks of fat and signal intensities similar to skeletal muscle. Ultrasound examination of elastofibroma has demonstrated a fasciculated structure with regular alternating hyperechoic and hypoechoic striae of varying thickness.
Elastofibroma is thought to be a degenerative, non-neoplastic pseudotumor arising as a result of excessive collagen deposition and abnormal elastogenesis secondary to mechanical irritation of the tissue plane between the inferior edge of the scapula and the chest wall. A genetic predisposition to this condition has been suggested.
Elastofibroma is often found incidentally either during a radiographic evaluation (such as for lung cancer) or at the time of thoracotomy. Its complete resection is considered curative with no tendency to recur.
The typical location of the described mass occurring in an elderly woman and characteristic histologic features will help to establish the correct diagnosis of elastofibroma. Other lesions should be considered in the differential diagnosis, but can be excluded using simple clinicopathologic criteria. Spindle cell lipoma also occurs in the shoulder/back region, but it is more common in men. It shows thick, rope-like collagen bundles and characteristic spindled cells, often admixed with mast cells. Low grade myxofibrosarcoma is rarely seen in the trunk region. It characteristically shows a distinct multinodular growth pattern, prominent myxoid matrix, curvilinear blood vessels and cytologic atypia. Nuchal-type fibroma is more common in men and shows thick, haphazardly arranged collagen fibers and elastic-poor fibrous tissue. Many cases are associated with diabetes mellitus. Desmoid-type fibromatosis shares the infiltrative pattern and poor margination with elastofibroma. However, it is usually hypercellular and associated with skeletal muscle. Elastofibroma in contrast is not muscle invasive. A myxoid variant of neurofibroma certainly enters the differential diagnosis but immunohistochemical staining for S-100 and the typical wavy nuclei help to distinguish it from elastofibroma.