This video presents a detailed pathological review of a hibernoma (Case 5), a rare, benign neoplasm derived from brown fat. The speaker highlights the distinct histological "beauty" of the tumor, which serves as a classic diagnostic case.
A key feature is the mixture of three cell types: regular adult white adipocytes; bubbly, multi-vacuolated cells (resembling mulberries or benign lipoblasts due to their uniform nuclei); and granular, eosinophilic cells. The granular appearance of the latter is attributed to a high concentration of mitochondria, which is characteristic of brown fat's thermogenic function. The speaker also discusses the clinical context, noting that hibernomas typically occur as large, deep soft tissue masses in young adults, making them a potential radiological mimic of liposarcoma due to areas of increased cellularity and water content compared to simple white fat.
Pathology Review of a Hibernoma (Brown Fat Neoplasm)
0:07 Case Identification: The case is identified as "Case 5," presenting cells that look like "mulberries," which is a quintessential feature of hibernomas or fatty tumors.
0:42 Diagnosis Confirmed: The diagnosis is a hibernoma, a benign neoplasm of brown fat. It is distinct from lipoma or regular white fat.
0:54 Normal Brown Fat Distribution: Normal brown fat is usually common in younger children but is occasionally seen in adults in deeper soft tissues (e.g., around the neck or kidneys), not typically in the subcutaneous layer.
1:18 Clinical Presentation & Rarity: Hibernomas typically occur in adults and present as larger, deeper masses. They are rarely seen in the skin or removed by dermatologists; they usually involve surgeons due to depth/size.
1:58 Three Cell Types: Hibernomas are composed of a mixture of three types of fat cells:
Regular white fat (large, univaculated cells).
Bubbly, multi-vacuolated cells (Mulberry cells). These resemble lipoblasts but have uniform, non-pleomorphic nuclei.
Red, pink, grainy, granular cells.
3:30 Lipid Vacuole Morphology: The clear, sharply circumscribed vacuoles are clue that they are lipid-based. They must push/scallop the nucleus because the nucleus is water-based while the vacuole is lipid (oil/water separation).
4:44 Mitochondria Richness (Key Takeaway): The red, grainy appearance of the third cell type is due to the cells being filled with mitochondria. This is linked to brown fatβs function of producing heat (thermogenesis), as implied by the name "hibernoma."
5:36 Histological Variation: Hibernomas vary significantly; some are mostly white fat with scattered mulberry/granular cells (more common in practice), while others are loaded with the characteristic bubbly and red cells (which are often selected for teaching sets).
6:07 Imaging Differential Diagnosis (Key Takeaway): The tumor often has numerous dilated capillaries and can be deep (this case was in the muscle). On MRI, hibernomas can mimic liposarcoma because they appear denser than normal fat due to their increased cellularity and water content.
7:20 Conclusion: The speaker expresses enthusiasm for the histology, noting the beautiful striations of the adjacent skeletal muscle.