Solitary myofibroma of the sigmoid colon: case report and review of the literature

Abstract

A 58-year-old woman presented with a solitary myofibroma that arose in the sigmoid colon. Computed tomography revealed a highly enhanced intramural mass (1.3-cm maximum diameter) in the proximal sigmoid colon. Histologically, the tumor exhibited a biphasic growth pattern, which comprised haphazardly arranged, interwoven fascicles of plump, myoid-appearing spindle cells with elongated nuclei and abundant eosinophilic cytoplasm, and more cellular areas of primitive-appearing polygonal cells that were arranged in a hemangiopericytomatous pattern. The tumor cells were positive for smooth muscle actin (SMA), and negative for desmin, h-caldesmon, CD34, cytokeratin, S100 protein, and CD117. The Ki-67 labeling index was not high (up to 7%). Based on these histologic and immunohistochemical features, our patient was diagnosed with a myofibroma of the sigmoid colon. The presence of solitary myofibroma in the intestine of an adult requires attention to avoid misdiagnosis as a more aggressive mesenchymal tumor.

Virtual slides: The virtual silde(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/2096403796957687.

Figure 1

Radiologic characterization of the lesion. CT imaging revealed a highly enhanced intramural mass (1.3 cm in maximum diameter; white arrows) in the proximal sigmoid colon.

Figure 2

Gross features of the lesion. A well-demarcated, ovoid 1.3 cm × 1.0 cm × 0.7 cm intramural mass (arrows) is noted in the colon.

Figure 3

Histologic features of the tumor. A. The tumor is well-demarcated and situated transmurally. There are alternating light and dark areas within the tumor (H&E, ×20). B. The light area consists of haphazardly arranged, interweaving fascicles of plump, myoid-appearing spindle cells with elongated nuclei and abundant eosinophilic cytoplasm (H&E, ×400). C. The dark, more cellular area consists of primitive-appearing polygonal cells arranged in a hemangiopericytomatous pattern (H&E, ×400). D. Intravascular proliferation of tumor cells is noted at the periphery of the lesion (H&E, ×200).

Figure 4

Immunohistochemical findings. A. The myoid-appearing spindle tumor cells show diffuse and strong positivity for SMA (immunostaining, ×400). B. The primitive-appearing tumor cells are focally positive for SMA (immunostaining, ×400). C. The myoid-appearing spindle tumor cells show an increased Ki-67 labeling index (up to 7%) (immunostaining, ×400). D. The primitive-appearing tumor cells display low Ki-67 labeling index (up to 1%) (immunostaining, ×400).