This transcript reviews a case of Granular Cell Tumor (GCT), emphasizing its classic histological features and the significant diagnostic pitfall posed by overlying epidermal changes. GCT is characterized by pale, granular cells infiltrating the dermis, often trickling between collagen bundles, and commonly showing benign perineural involvement. The main focus is on the pseudoepitheliomatous hyperplasia (PEH) that GCT incites in the epidermis, which can strongly mimic invasive squamous cell carcinoma (SCC). The speaker provides a critical warning, noting that misdiagnosing this reactive hyperplasia, particularly in mucosal sites like the tongue, can lead to severe and unnecessary surgical intervention. Pathologists are advised to search for the characteristic granular cells between the hyperplastic keratinocyte islands to confirm the diagnosis.
Granular Cell Tumor (GCT) and the Pitfall of Pseudoepitheliomatous Hyperplasia
0:26 Low Power Appearance: Granular Cell Tumor classically appears as pale cells filling the dermis and "trickling between" (infiltrating) the collagen bundles, a characteristic pattern.
1:01 Cellular Morphology & Stains: The cells have granular cytoplasm due to accumulated phagolysosomes, sometimes containing "pustulo ovoid bodies of million." GCTs stain positive for S100, CD68, and PAS.
1:25 Perineural Involvement: Almost 90% of GCTs exhibit perineural involvement (tumor cells wrapping around nerves). This is a normal, benign finding and is not considered worrisome.
1:38 The Diagnostic Trap: The main difficulty is the reactive proliferation in the overlying epidermis, which strongly resembles squamous cell carcinoma (SCC).
2:01 Pseudoepitheliomatous Hyperplasia (PEH): The epidermal change is diagnosed as pseudoepitheliomatous hyperplasia (PEH), a benign, reactive epidermal growth commonly incited by GCT. This reaction can also be seen in conditions like invasive fungal infections or bromoderma.
2:23 Critical Warning (Mucosal Sites): PEH associated with GCT is particularly dangerous in mucosal sites (e.g., the tongue). A misdiagnosis of SCC in this location could lead to radical surgery, such as a hemiglossectomy.
2:43 Key Takeaway for Pathologists: If viewing a potentially bland SCC, specifically look between the islands of keratinocytes for the characteristic granular cells. Their presence confirms the diagnosis of GCT with reactive PEH, preventing misdiagnosis.
3:00 Varied Mimicry: GCT can cause the epidermis to grow in various strange ways, including mimicking lesions like a wart (as seen in a case on the foot).