This transcript details the pathology of a Granular Cell Tumor (GCT), a massive lesion characterized by large, pale cells with prominent intracytoplasmic granules, often mistaken for histiocytes. The speaker confirms that GCTs are neuroectodermal in origin, derived from Schwann cells (a type of nerve sheath tumor). Diagnosis relies heavily on the H&E appearance (granular cytoplasm, low mitotic rate) and characteristic immunostaining (S100, SOX10, and non-specifically CD68). Key features discussed include the tumor's benign nature, the potential pitfall of associated pseudoepitheliomatous hyperplasia (PEH) mimicking squamous cell carcinoma, the unencapsulated "feathery" border, and the common finding of perineural growth reflecting its neural sheath lineage.
Summarizing the Pathology of Granular Cell Tumor (GCT)
0:07 Case Introduction: Discussion of a massive tumor (Case 14) exhibiting large, pale areas.
0:17 Microscopic Appearance: Examination at higher power shows large, granular-appearing cells (histiocytes/hyocytes) containing distinct cytoplasmic granules. This morphology is characteristic of a Granular Cell Tumor (GCT).
0:32 Origin (Key Takeaway): Despite their histiocyte-like appearance, GCTs are actually nerve sheath tumors derived from Schwann cells.
0:55 Immunostaining Profile: The tumor cells stain positively for S100 and SOX10 (neural markers). They also stain with CD68, which is a marker for phagolysosomes (phagocytic activity) and is therefore non-specific in this context, as GCT cells contain abundant phagosomes.
1:27 Special Stains: PAS (Periodic acid–Schiff) stain will beautifully highlight these characteristic cytoplasmic granules. The diagnosis is generally considered an H&E diagnosis.
1:44 Biological Behavior: The vast majority of GCTs are totally benign. Malignant versions are exceedingly rare and are identified by features like numerous mitoses or severe pleomorphism.
2:06 Cytoplasmic Features: GCT cells are distinct from xanthomas (bubbly, vacuolated cytoplasm), instead featuring speckled pink dots and granular globules in the cytoplasm, sometimes referred to as postulo ovoid bodies of million. Nuclei are typically round with low mitotic activity.
2:41 Nuclear Atypia: GCTs, like other nerve sheath tumors (schwannomas, neurofibromas), can exhibit scattered degenerative or random pleomorphism, which is an expected finding and not worrisome for malignancy if other features (like mitosis) are absent.
3:29 Diagnostic Pitfall (Key Takeaway): GCTs frequently induce striking pseudoepitheliomatous hyperplasia (PEH) in the overlying epidermis (particularly in mucosal sites like the tongue), which can mimic a glassy, well-differentiated squamous cell carcinoma (SCC) or a verruca (wart). Pathologists must look for the granular cells in the underlying dermis/submucosa.
4:30 Tumor Border: GCTs are not encapsulated or sharply circumscribed. They characteristically have a "feathery" or "infiltrative" border where cells trickle out and interdigitate between the dermal collagen bundles.
5:04 Perineural Growth (Key Takeaway): It is very common (present in almost 90% of cases) for GCT cells to grow around adjacent nerve bundles due to their Schwann cell origin; this finding should not be mistaken as a sign of malignancy.