Case Presentation - Spring, 2014

Fat Necrosis

Written by: Maria Lopez, student, Cleveland Clinic School of Cytotechnology, Cleveland, Ohio

Patient Age and History: Female, age 46

Specimen type: FNA-Left Breast, ThinPrep® Non-Gyn cytology

Patient History: Status post bilateral mastectomies for Grade 2 Infiltrating Ductal Carcinoma approximately 1 year prior. Now with mass at mastectomy site on left

Cytologic diagnosis: Negative, consistent with fat necrosis

Case provided by: Milstead Pathology, Conyers, Georgia

Organizing Fat Necrosis

Fat necrosis of the breast is a phenomenon that occurs within breast adipose tissue following exposure to trauma. A wide range of occurrences can cause trauma but physical injuries, such as accidental falls and damage relating to surgical procedures such as lumpectomy, are the most common. Other causes include implant removal, breast reconstruction, biopsy, mammary duct ectasia, breast infection, and exposure to radiotherapy. As a result of the trauma, the adipocytes undergo necrosis and a benign inflammatory process results from the saponification of fat by blood and tissue lipase.1 Microcalcification and lipid cyst formation can occur but cystic degeneration can leave behind an oil filled cavity. The calcifications that develop within the cyst walls are surrounded by fibrosis, and these can be detected by mammography.

Clinical Features:
Both females and males can be diagnosed with fat necrosis of the breast. Symptoms may or may not manifest; however, when present the clinical features can vary. Some patients may have a single, smooth rounded lump while others may possess multiple lumps. Irregular masses with overlying skin retraction may also be present. Other features associated with underlying fat necrosis include pain, skin thickening or retraction, nipple retraction, erythema, ecchymosis, and lymphadenopathy.1,6 Furthermore, mammographic features of fat necrosis also vary depending on the amount of fibrosis present. Minimal fibrosis is associated with earlier stages, where the lesion is seen as an oil cyst or a radiolucent mass. Calcifications will develop in the progression of fat necrosis and these can take on either a benign, ring-like structure or rod-like, irregular shapes suspicious for malignancy.

Treatment and Prognosis:
Because fat necrosis of the breast presents in various ways, management does not follow strict guidelines. Rather, it is contingent upon the presenting symptoms and the combined assessment of imaging findings and FNA biopsy. Fat necrosis should resolve itself, so the lesions are generally not removed immediately. If the mass does not decrease in size or if it grows, surgical excision occurs to rule out a malignancy. If pain presents, pain medication can also be prescribed at various levels (narcotics or non-narcotic analgesics).

On FNA biopsy it is possible to sense a grainy texture through the penetrating needle. Greasy material will be collected and may bead up on air-dried slides. Smears of fat necrosis are generally hypocellular. There will be varying amounts of infiltrating histiocytes, hemorrhage, fibrosis, and calcification visualized based on the progression of fat necrosis. The typical cytological presentation includes histiocytes with foamy, vacuolated cytoplasm, multinucleated giant cells, blood pigment, and possibly foreign body granulomas. Neutrophils, lymphocytes, and plasma cells can be seen in the background with acute inflammation predominating in the earlier stages. Chronic inflammation will predominate in the later stages and it, along with the formation of granulation tissue and fibrosis, can result in the creation of scar tissue which can mimic cancer. The few epithelial cells present may be considered atypical because of their prominent nucleoli, nuclear pleomorphism, hyperchromasia, and mitotic figures.3

Differential Diagnosis:
Due to the various mammographic features of fat necrosis of the breast and the presence of a worrisome mass, one of the major differential diagnoses of this phenomenon is a malignancy. Even a diagnosis of fat necrosis on a biopsy specimen cannot rule out malignancy because both can occur simultaneously. For example, certain ductal carcinomas have been known to coexist with fat necrosis and have a distinct population of malignant cells in conjunction with the typical histiocytes seen. Another carcinoma that may be confused with fat necrosis is lipid-rich carcinoma because although rare, its tumor cells also have vacuolated cytoplasm. The difference, however, is that lipid-rich carcinoma will have an abundance of cells with atypical nuclear features while an aspirate of fat necrosis is hypocellular. In addition to malignancies, cryptococcosis of the breast can also be considered in the differential diagnosis because histiocytes with large cytoplasmic vacuoles are seen with this infection. However, refractile budding yeast forms can be identified within these histiocytes and this generally occurs in immunocompromised patients. For patients with a history of silicone injections or a ruptured silicone implant, a silicone granuloma may be in the differential. The histiocytes seen in this lesion also contain vacuoles but they are not as large as those identified in fat necrosis. 2

  1. Aqel NM, Howard S, Collier DS. Fat Necrosis of the Breast: A Cytological and Clinical Study. The Breast. 2001;10:342-45. Ohio Link. Web Accessed January 7, 2014.
  2. Cibas ES, Ducatman BS. Breast. In: Cytology: Diagnostic Principles and Clinical Correlates. 3rd ed. Philadelphia, PA: Saunders Elsevier; 2009:232-33.
  3. DeMay RM. Breast. In: The Art and Science of Cytopathology: Aspiration Cytology. Chicago, IL: American Society of Clinical Pathologists; 1996:858.
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  5. Taboada JL, Stephens TW, Krishnamurthy S, Brandt KR, Whitman GJ. The Many Faces of Fat Necrosis in the Breast. AJR Women's Imaging. 2009;192(3):815-25. Ohio Link. Web Accessed January 7, 2014.
  6. Tan PH, Lai LM, Carrington EV, Opaluwa AS, Ravikumar KH, Chetty N, Kaplan V, Kelley CJ, Babu ED. Fat Necrosis of the Breast-A Review. The Breast 2006;15(3): 313-18. Ohio Link. Web Accessed January 7, 2014.