This transcript details the microscopic examination and diagnostic features of a granular cell tumor (GCT). The speaker highlights the tumor's characteristic appearance under the microscope, including large, pale, histiocyte-like cells with prominent cytoplasmic granules. Crucially, the video explains that GCTs are actually nerve sheath tumors originating from Schwann cells, despite their resemblance to histiocytes, and confirms this with their typical positive staining for S100, SOX10, and PAS (for granules), as well as CD68 (a non-specific marker for phagolysosomes). The discussion emphasizes the overwhelmingly benign nature of GCTs, outlining rare criteria for malignancy. Furthermore, the speaker describes important architectural features such as pseudoepitheliomatous hyperplasia (which can mimic squamous cell carcinoma), their typically infiltrative borders, and their common association with nerve bundles, reassuring viewers that the latter is a normal finding for this type of tumor.
Exploring Granular Cell Tumors: A Microscopic Case Study
0:07 Tumor Appearance: The case presents a large, pale tumor characterized by large, granular histiocyte-like cells, which are key to identifying a granular cell tumor.
0:48 Schwann Cell Origin: Despite their histiocyte-like appearance, granular cell tumors are actually nerve sheath tumors originating from Schwann cells.
0:55 Key Immunostains: These tumors typically stain positive for S100 and SOX10, confirming their neural origin. They also stain with CD68 (a marker for phagolysosomes, not specific to histiocytes) and show beautiful staining with PAS due to the cytoplasmic granules.
1:32 Benign Nature: Granular cell tumors are almost always benign; malignant versions are exceedingly rare and have specific criteria (e.g., high mitosis, pleomorphism). Most diagnoses are made based on H&E staining.
2:01 Differentiating Features: The cells contain "speckled stippled pink dots" and "granular globules" (called Postulo-ovoid bodies of Million), which distinguish them from xanthomas that have bubbly, vacuolated cytoplasm.
3:36 Cellular Characteristics: Typically, the cells have round nuclei, central punctate nucleoli, and low mitotic activity. Random pleomorphism (degenerative atypia) is common and acceptable in nerve sheath tumors, not indicative of malignancy unless accompanied by other worrying features.
3:29 Pseudoepitheliomatous Hyperplasia: A significant pitfall is that granular cell tumors can induce striking pseudoepitheliomatous hyperplasia in the overlying epidermis, potentially mimicking well-differentiated squamous cell carcinoma or even warts, especially in mucosal sites like the tongue. One should look for the characteristic granular cells in the dermis/submucosa to differentiate.
4:28 Infiltrative Border: Granular cell tumors usually have a "feathery," "infiltrative" border where cells intercollate with dermal collagen bundles, rather than being sharply circumscribed or encapsulated.
5:01 Perineural Growth: It is very common (almost 90% of cases) for granular cell tumors to grow around nerve bundles at the periphery. This is a normal finding for a nerve sheath tumor and should not be misinterpreted as a sign of malignancy.