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Case number:	165
Age:	56
Clinical presentation:	Postmenopausal woman with average risk of breast cancer presented with a left breast lump and mastalgia noticed 1 week ago.

Mammography:

Breast composition:	ACR category b (there are scattered areas of fibroglandular density)
Mammography features:
‣ Location of the lesion:	Left breast, upper inner quadrant at 11 o’clock, posterior third
‣ Mass:
• Number:	1
• Size:	2.6 × 1.7 cm
• Shape:	Irregular
• Margins:	Indistinct
• Density:	Equal
‣ Calcifications:
• Typically benign:	None
• Suspicious:	None
• Distribution:	None
‣ Architectural distortion:	None
‣ Asymmetry:	None
‣ Intramammary node:	None
‣ Skin lesion:	None
‣ Solitary dilated duct:	None
‣ Associated features:	None

Ultrasound:

Ultrasound features: Left breast, upper inner quadrant at 11 o’clock, 10.2 cm from the nipple and at 1.0 cm skin depth
‣ Mass
• Location:	Left breast, upper inner quadrant at 11 o’clock, 10.2 cm from the nipple and at 1.0 cm skin depth
• Number:	1
• Size:	2.0 × 1.0 cm
• Shape:	Oval
• Orientation:	Parallel
• Margins:	Circumscribed, 2–3 lobulations present
• Echo pattern:	Heteroechoic with central anechoic component
• Posterior features:	No posterior features
‣ Calcifications:	None
‣ Associated features:	None
‣ Special cases:	None

BI-RADS:

BI-RADS Category: 2 (benign)

Further assessment:

Further assessment advised: Referral for cytology

Cytology:

Cytology features:
‣ Type of sample:	FNAC
‣ Site of biopsy:
• Laterality:	Left
• Quadrant:	Upper inner
• Localization technique:	Palpation
• Nature of aspirate:	0.5 mL of thin greyish fluid
‣ Cytological description:	Smears reveal foamy macrophages, a few multinucleated giant cells, numerous lymphocytes, and occasional ductal epithelial cells on a background of granular debris, fat droplets, and fragments of adipose tissue
‣ Reporting category:	Benign
‣ Diagnosis:	Consistent with fat necrosis
‣ Comments:	None

Case summary:

Postmenopausal woman presented with a painful left breast lump. Diagnosed as fat necrosis, BI-RADS 2 on imaging and as benign fat necrosis on cytology.

Learning points:

Fat necrosis is a benign, non-suppurative inflammatory process of adipose tissue. It is important to diagnose fat necrosis because it can often mimic carcinoma of the breast. The histological appearance of fat necrosis depends on the age of the lesion, progressing from inflammation to necrosis showing liquefied fat and finally to fibrosis.