This video presents a lecture by Dr. Jared Gardner, showcasing six complex and high-yield cases in dermatopathology and soft tissue pathology using digital slides and static images. The discussion focuses on tumors that often present diagnostic challenges or mimic other entities.
Key cases reviewed include a Glomus tumor with eosinophilic and clear cell change mimicking a sweat gland neoplasm (hidradenoma), and a highly unusual Matrix-producing melanoma exhibiting heterologous chondro- and osteosarcomatous differentiation. Dr. Gardner also provides a detailed look at Schwannoma, emphasizing the recognition of subtle palisading ("Antoni A" features) and "Ancient Change" (pleomorphism) in the absence of classic Verocay bodies, contrasting it with Palisaded Encapsulated Neuroma (PEN). The lecture also covers the diagnostic features of Kaposiform Hemangioendothelioma (KHE) / Tufted Angioma and Calcifying Aponeurotic Fibroma. It concludes with an example of an exceedingly rare infestation: a Bot Fly larva (myiasis).
Dermatopathology Case Review: Mimics, Rare Variants, and Subtle Features
Patient/Presentation: 30-year-old man with a large, multi-nodular, 4 cm foot nodule (plantar foot).
Features: Alternating areas of dark blue (small, round cells) and pale pink (eosinophilic/plasmacytoid cells). Embedded in dense hyalinized stroma.
Differential: Initially considered Dermal Duct Tumor or Hidradenoma due to pale/eosinophilic areas.
Stains & Takeaway (3:24): Ultimately diagnosed as a large Glomus Tumor. Glomus tumors can mimic sweat gland neoplasms. Key clues include small round glomus cells tracking along vessels at the periphery (5:01) and strong Smooth Muscle Actin positivity in perivascular regions (7:01). PAS stain (6:17) highlights the basement membrane surrounding individual glomus cells.
Patient/Presentation: 60-year-old man with a nodule on the face (chin), thought to be a cyst.
Features: Fragmented specimen showing hypercellular, atypical chondrocytes (9:20, suggestive of chondrosarcoma) and dense sclerotic collagen mineralizing into irregular bone (9:54, suggestive of osteosarcoma). The periphery features sheets of markedly atypical, hyperchromatic spindle cells with frequent mitoses (11:42).
Stains & Diagnosis (12:30): Keratin and P63 were negative; Sox 10 was positive. Diagnosed as a Spindle Cell Melanoma with heterologous osteosarcomatous and chondrosarcomatous differentiation (Matrix-producing melanoma).
Takeaway (13:58): This is an extremely rare example of melanoma de-differentiating and re-differentiating into heterologous matrix (bone/cartilage). Always include melanoma and carcinoma (like basal cell) in the differential for osteo/chondrosarcoma appearing in the skin, in addition to reactive processes (16:35).
Patient/Presentation: Adult woman with a deep popliteal mass.
Features: Thick capsule, sharp circumscription, and classic Antoni A (hypercellular) and Antoni B (hypocellular/myxoid) zones (19:29). Common findings include dilated vessels, hemorrhage, hemosiderin, and perivascular hyalinization/sclerosis (19:43, 29:14).
Diagnostic Challenge (20:19): This case lacked classic Verocay bodies. Diagnosis relies on recognizing subtle nuclear palisading (21:10) and scattered hyperchromatic, pleomorphic cells ("random pleomorphism" or "ancient change") (22:31).
Takeaway (24:08): Pleomorphism is common and acceptable in schwannomas. Schwannomas are composed almost entirely of Schwann cells and should be strongly and diffusely positive for S100 and Sox10, unlike Neurofibroma.
29:52 Case 3b: Schwannoma vs. Palisaded Encapsulated Neuroma (PEN)
Distinction: Schwannomas are "exceptionally rare" in the dermis (28:04). PEN (Solitary Circumscribed Neuroma) is the much more likely dermal diagnosis on a board exam.
Key PEN Feature (31:35): PEN lacks the thick capsule of schwannoma and is characterized by a "crack-like clefting artifact" around the fascicles of spindle cells.
33:06 Case 4: Kaposiform Hemangioendothelioma (KHE) / Tufted Angioma
Patient/Presentation: 12-year-old boy with a slowly growing violaceous plaque on the back present since birth.
Features: Sclerotic dermis, multiple dilated lymphatic channels (35:41), and characteristic "cannonball-like" nodules (35:50) composed of very tightly compressed vascular channels. These nodules characteristically trap platelets (CD61 positive).
Diagnosis & Takeaway (36:00): KHE and Tufted Angioma are considered part of the same biological spectrum (WHO classification). KHE, when large and deep, especially in infants, is associated with Kasabach-Merritt Syndrome (thrombocytopenia due to platelet trapping), which is the main cause of mortality in KHE (37:20). Management requires careful consideration of surgical vs. medical therapies (e.g., Sirolimus) (39:40).
42:38 Case 5: Calcifying Aponeurotic Fibroma (CAF)
Patient/Presentation: Palmar mass in a child (classic location).
Features: Defined by a triad of fragmented calcifications, surrounding round cells radiating outward like "spokes on a wheel" (43:16, 46:11), and background spindle cells arranged in sweeping fascicles (like desmoid fibromatosis).
Takeaway (44:39): CAF is a rare benign tumor common in hands and feet. It is locally infiltrative and has a significant tendency for local recurrence (45:18), often many years later. Management must balance complete excision against functional morbidity, especially in the hands of children.
Patient/Presentation: Highly unusual case showing a large arthropod.
Features: Large arthropod located in a cystic space within the dermis, connected to an epidermal tract (47:10). Microscopic detail shows striated skeletal muscle and a yellow, refractile chitin exoskeleton (47:28).
Takeaway: This is a Bot Fly larva (maggot). Distinguishing features include the organism's large size and its deep location within a cystic space (ruling out typical scabies or ticks).