This video presents a dermatopathology case study (Case 9) concerning a nodule on the back of a 25-year-old woman, ultimately diagnosed as a Granular Cell Tumor (GCT). The microscopic examination reveals the characteristic features of GCT: unencapsulated nests and cords of plump, eosinophilic cells with abundant granular cytoplasm, infiltrating the dermal collagen. The primary educational focus is on the observation of perineural involvement (tumor cells completely wrapping around peripheral nerves). The speaker emphasizes that, due to its neural sheath origin, this finding is expected, benign, and present in the vast majority (up to 90%) of GCT cases, requiring no clinical concern or mention in the report unless specifically questioned.
Granular Cell Tumor with Benign Perineural Involvement
0:09 Case Introduction: The presentation is Case 9: a nodule found on the back of a 25-year-old woman.
0:24 Key Diagnostic Clue (Perineural Involvement): The initial images show tumor cells completely wrapped around a peripheral nerve, described as a "donut around the nerve." This perineural involvement is central to the discussion.
1:22 Morphological Description: The tumor is composed of an abundance of polygonal, plump, eosinophilic cells with granular cytoplasm, forming nests and cords.
1:49 Infiltrative Growth Pattern: The tumor is not well-circumscribed or encapsulated; it “trickles out” throughout the dermis, weaving between background collagen. This pattern does not imply aggressive behavior but is characteristic of GCT growth.
2:11 Diagnosis Confirmation: The tumor is confirmed as a Granular Cell Tumor (GCT). GCTs are tumors of neural sheath origin and are expected to be strongly S100 positive.
2:48 Significance of Nerve Involvement: Perineural involvement in GCT is benign and common, found in up to 90% of cases. It should not be referred to as "invasion" as it lacks malignant significance. The speaker advises against mentioning this feature in the final report unless it is specifically consulted upon, as it is a normal finding for this entity.
4:38 Immunohistochemistry (IHC): GCTs are S100 and SOX10 positive (neural markers). They are also CD68 positive because the granular cytoplasm is filled with phagolysosomes (CD68 is a phagolysosome marker, not a specific histiocyte marker). PAS stain can also be used to highlight the granular cytoplasm.
5:49 Atypical Features (Benign vs. Malignant): Random, scattered nuclear polymorphism (atypia) is common and benign in GCTs. Features that should raise concern (suggesting atypical or malignant GCT) include spindling, large nucleoli, and mitotic activity.
6:43 Associated Epidermal Changes: GCTs, particularly in common sites like the tongue, can induce extensive pseudoepitheliomatous hyperplasia in the overlying epidermis or mucosa, which can strongly mimic invasive squamous cell carcinoma, but is reactive and benign.
7:34 Pustulo-Ovoid Bodies of Million: These are small, clustered aggregates of granules visible in the cytoplasm, noted as a recognized but non-essential finding for the diagnosis.