This video provides a histological comparison between fibromatosis (a fibroblastic/myofibroblastic tumor) and smooth muscle tumors, using leiomyoma as a contrasting example. At high power, the defining feature of fibromatosis is the presence of spindle cells with bland nuclei, bluish/purplish cytoplasm, and abundant, fine pink wavy strands of extracellular collagen separating the cells. In contrast, smooth muscle tumors like leiomyoma, while also composed of spindle cells, exhibit bright pink cytoplasm (derived from contractile filaments) and characteristically lack significant intervening collagen deposition, making high-power cellular and matrix assessment critical for differentiation.
Histological Comparison of Fibromatosis and Leiomyoma
0:00 Fibromatosis (High Power): Characterized by cells with bland nuclei and minimal atypia. Individual spindle cells have bluish or purplish cytoplasm located at one or both ends of the nucleus.
0:18 Hallmark Feature of Fibromatosis: Tumor cells are separated by fine, wavy, pink strands of extracellular collagen. This separation via collagen deposition is the defining characteristic of any fibroblastic or myofibroblastic process.
0:44 Contrast with Smooth Muscle Tumors: Smooth muscle tumors (like leiomyoma) also have spindle-shaped cells, but they possess bright pink cytoplasm (rather than bluish/purple) and do not usually feature much intervening collagen.
0:57 Leiomyoma (Low Power): May appear similar to fibromatosis, showing monotonous spindle cells running in broad fascicles.
1:11 Leiomyoma (High Power): The tumor cells lack the distinctive bluish/purple cytoplasm seen in fibromatosis. Instead, they exhibit a pink, stringy cytoplasm.
1:28 Source of Pink Cytoplasm in Leiomyoma: The pink color comes from the contractile filaments within the smooth muscle cells, not from extracellular collagen.
1:36 Key Differentiating Feature: Leiomyomas have very little, if any, collagen separating the individual cells, which is a useful feature at high power to distinguish them from fibroblastic tumors like fibromatosis.