Okay, here is the abstract and summary for the Panniculitis review video transcript.
Abstract:
This educational video features Dr. Jerad Gardner reviewing various forms of panniculitis (inflammation and necrosis of subcutaneous fat) and their histological mimics with pathology residents and fellows. The session covers a wide range of entities, emphasizing key microscopic features, differential diagnoses, clinical correlations, and diagnostic pitfalls. Specific conditions discussed include pancreatic panniculitis with its characteristic saponification, lupus panniculitis (profundus) featuring hyalinized fat necrosis, subcutaneous fat necrosis of the newborn with unique crystalline structures, lipoatrophy, calciphylaxis showing vascular calcification and ischemia, eosinophilic fasciitis involving septal/fascial sclerosis, and various mimics like ruptured cysts, hidradenitis suppurativa, encapsulated fat necrosis, silicone granulomas, and subcutaneous panniculitis-like T-cell lymphoma. The importance of adequate biopsy depth and clinical context for accurate diagnosis is stressed throughout the case discussions.
Panniculitis and Mimics: A Dermatopathology Review
Caused by pancreatic enzymes (like lipase) leaking into the bloodstream (due to pancreatitis, tumor, etc.) and damaging subcutaneous fat.
Histology: Shows characteristic fat necrosis with "ghost outlines" of adipocytes, a grungy/fibrillary appearance, and prominent saponification (fat combining with calcium, appearing blue/purple), sometimes likened to "garlic in cross-section". Can have associated inflammation.
Key Takeaway: Distinct pattern of fat necrosis linked to pancreatic disease; the saponified pattern can persist long after the acute event. Mentioned Alpha 1 antitrypsin deficiency panniculitis can look similar but often has more neutrophils.
Inflammation of fat associated with lupus erythematosus. May occur with or without overlying skin changes of lupus.
Histology: Features varying adipocyte sizes, loss of adipocyte nuclei (necrosis), hyalinized/fibrotic necrosis between fat cells, often with lymphocytic infiltrate (B and T cells), plasma cells, and sometimes lymphoid follicles with germinal centers. Overlying skin may show interface dermatitis.
Shrinking of fat cells, not primarily inflammation or necrosis.
Histology: Adipocytes are markedly reduced in size but retain lobular architecture. Appears hypercellular due to nuclei and capillaries becoming crowded together. Vessels may resemble "chicken wire" pattern. Individual cells can look like tiny signet ring cells.
Causes: Steroid injection, trauma, pressure, starvation/malnutrition, certain syndromes, advanced AIDS, sometimes associated with fat necrosis.
Pitfall: Can mimic signet ring cell carcinoma (use keratin stain to differentiate) or liposarcoma. Seeing the lobular pattern helps.
Occurs in term infants, often after stressful birth. Presents as firm, reddish/violaceous nodules, typically self-resolving.
Histology: Fat necrosis with mixed inflammation (lymphocytes, histiocytes, giant cells) and characteristic needle-shaped, radially arranged clefts/crystals within adipocytes and giant cells (representing dissolved triglycerides/fatty acids).
Key Takeaway: Distinctive crystals are key. Thought to be due to different fatty acid composition in infant fat crystallizing more easily. Sclerema neonatorum is a clinically distinct, more severe condition. Similar crystals can be seen in fat necrosis from other causes (e.g., angioinvasive fungus) in infants.
Benign tumor of brown fat, not a panniculitis. Usually occurs in young adults, often deep (not typically skin/subcutis).
Histology: Mixture of three cell types: mature white fat, multivacuolated "mulberry" cells (like lipoblasts but with uniform nuclei), and granular eosinophilic cells (rich in mitochondria). Cells have round nuclei with prominent nucleoli, but are uniform. Rich capillary network.
Key Takeaway: Recognizable mix of cell types. Important mimic of liposarcoma on imaging due to being a deep fatty mass with non-fatty components.
Serious condition, often in patients with end-stage renal disease and altered calcium/phosphate metabolism. Presents as painful, indurated plaques that necrose.
Histology: Key is calcification of small vessel walls (capillaries, arterioles) in the subcutis, often associated with fibrin thrombi and ischemic necrosis of overlying skin (epidermis/dermis) and fat. May see fine or chunky calcium deposits in necrotic fat or around eccrine coils.
Key Takeaway: Diagnosis relies heavily on clinical context (renal failure, painful necrotic lesions). Look for small vessel calcification +/- thrombi and ischemia. Differential includes other causes of vascular calcification (e.g., Monckeberg's sclerosis in larger arteries - less specific). Von Kossa stain highlights calcium.
Presents as firm, "woody" induration, often on limbs, fixed to underlying structures. Considered a form of deep morphea/scleroderma.
Histology: Requires deep biopsy including fascia. Shows marked sclerosis (thickened collagen) of deep subcutaneous septa and/or fascia, with lymphoplasmacytic infiltrate. Eosinophils may be present but are often absent despite the name.
Key Takeaway: Diagnosis requires deep biopsy showing septal/fascial sclerosis. Eosinophils are not required. Scurvy mentioned as a rare clinical mimic.
53:24 Ruptured Cyst with Keratin Granuloma (Mimic):
Common finding presenting as an inflamed nodule.
Histology: Shows features of cyst rupture: fragments of keratin (key finding), foreign body giant cell reaction forming granulomas around keratin, mixed inflammation (neutrophils, lymphs, plasma cells, sometimes EOS), granulation tissue, fibrosis, and fat necrosis.
Key Takeaway: Finding keratin flakes explains the robust inflammation and distinguishes it from primary panniculitis or infection (though infection can co-exist). Clinical context (pilonidal, hidradenitis) is important.
Considered a "tuberculid" - an immune reaction to tuberculosis elsewhere in the body.
Histology: Mixed septal and lobular panniculitis. Features necrotizing granulomas, often centered around damaged vessels (vasculitis). Mixed inflammation.
Key Takeaway: Diagnosis requires ruling out infection (stains, culture). If infection negative, consider workup for TB (Quantiferon Gold, chest X-ray) and systemic vasculitis (e.g., ANCA). Primarily lobular granulomas with necrosis and potential vascular damage.
Common form of panniculitis, presenting as tender red nodules, often on lower legs of young women.
Histology: Primarily a septal panniculitis (though some lobular spillover is common). Early lesions show edema, hemorrhage, mixed inflammation (lymphs, histiocytes, neutrophils, EOS) in septa. Later, see granulation tissue, fibrosis, and Miescher's radial granulomas (small clusters of histiocytes around clefts).
Key Takeaway: Classic septal panniculitis. Appearance varies with lesion age.
Chronic inflammatory condition in intertriginous areas (axillae, groin).
Histology: Can show features overlapping with ruptured cysts/follicles: inflamed cyst/tract lining, rupture, keratin granulomas, sinus tracts, dense mixed inflammation (lymphs, plasma cells+++, neutrophils), granulation tissue, fibrosis, abscesses.
Key Takeaway: Diagnosis relies heavily on clinical presentation and location. Histology is often nonspecific inflammation/ruptured follicle pattern seen also in pilonidal disease or simple ruptured cysts.
Presents as a firm, often mobile, marble-like subcutaneous nodule, often following trauma.
Histology: Nodule of necrotic fat ("mummified" adipocytes, often lacking nuclei) sharply demarcated by a fibrous capsule. Minimal inflammation usually. May calcify or liquefy. Surrounding fat may show some atrophy.
Key Takeaway: Well-circumscribed nodule of dead fat with a fibrous wall. Often clinically mobile ("mobile lipoma" misnomer).
Foreign body reaction to leaked silicone (e.g., from older ruptured breast implants).
Histology: Extensive foreign body granulomatous reaction with numerous histiocytes and giant cells containing clear, non-polarizing, refractile vacuoles/globules of silicone of varying sizes. Creates appearance of "Swiss cheese" fat necrosis due to large clear spaces where silicone resided. Actual fat necrosis may also be present.
Key Takeaway: Look for the characteristic clear, refractile silicone material within giant cells/histiocytes amidst a granulomatous reaction.
Histology: Atypical lymphocytes infiltrate fat lobules, classically showing "rimming" or "hugging" of individual adipocytes. Lymphocytes often appear hyperchromatic and atypical. Karyorrhexis (nuclear debris) and "bean bag cells" (histiocytes phagocytosing debris) can be seen. Fat necrosis may be present but often less fibrinoid/hyalinized than in lupus panniculitis.
Key Takeaway: Important mimic of lupus panniculitis. Look for atypical lymphocytes rimming adipocytes. Immunostains are crucial to confirm T-cell lineage (CD3+, CD8+, TIA1+, BetaF1+), distinguish from lupus (less B-cells/plasma cells/follicles than lupus), and differentiate from the aggressive Gamma-Delta T-cell lymphoma (which is often CD56+, BetaF1- and involves dermis/epidermis more).