March 2019

A 64-year-old man with an 8-year history

of a slow-growing lower extremity soft tissue mass

Contributors: 

Carlo De la Sancha M.B

Resident Physician PGY-2, Anatomic and Clinical Pathology

Indiana University School of Medicine

Professional Interests: Cytopathology and Surgical Pathology

and

Chen Zhang, MD, PhD

Assistant Professor of Clinical Pathology & Laboratory Medicine

Indiana University School of Medicine

Clinical history: 

The patient is a 64-year-old gentleman with a history of hypertension who presented to an outside clinic with left hip pain and bilateral lower extremity neuropathy. A previous history of a small mass in the left lateral upper leg 8 years before, which was decided to be monitored, was noted. An MRI was done and showed a large extraskeletal mass in the soft tissues posterior to the proximal femur, densely adherent to the inferior gluteus maximus and following the sciatic nerve for a distance of at least 6cm (Figure 1). Initial differential diagnosis included hemangioma versus soft tissue sarcoma.

Figure 1: MRI shows an 8cm extraskeletal mass posterior to the femur, densely adherent to the gluteus maximus

Frozen section diagnosis:

Spindle cell neoplasm with low grade cytological atypia

Gross description:

The specimen consisted of an 8.5 x 5.9 x 3.7 red-tan to gray-tan, heterogeneous, myxoid mass with 10% of hemorrhage and 15% degeneration.

Microscopic description:

On microscopic examination the mass was composed of a multilobular proliferation of uniform spindled to rhabdoid cells with round-oval nuclei and eosinophilic cytoplasm embedded in abundant pale-blue myxoid matrix. The cells were arranged in cords and fine networks with wisps of eosinophilic cytoplasm that interconnected with each other. Areas of hemorrhage and hemosiderin deposition were also identified (Figure 2A-C)

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Fig. 2A . Low magnification photomicrograph shows a proliferation of spindle cells embedded in a myxoid stroma. Hemosiderin deposition is evident. (H&E. 40X)

Fig 2B: Spindle cells are arranged in a fine network and interconnected with each other by wisps of eosinophilic cytoplasm. (H&E. 200X)

Figure 2B

Fig.2C Some of the tumor cells display rhabdoid morphology. (H&E. 400X)

Fig 2C

Ancillary Studies

Immunohistochemical staining for SMARCB1/INI1 showed retained diffuse nuclear staining of the cells, including cells with rhabdoid morphology. (Figure 3)

Fig.3: Tumor cells demonstrate retained expression of SMARCB1/INI1.

March 2019 Final Diagnosis and Discussion