Inflammatory / infectious


Editorial Board Member: Emily S. Reisenbichler, M.D.
Editor-in-Chief: Debra L. Zynger, M.D.
Mary Ann G. Sanders, M.D., Ph.D.

Last author update: 1 June 2018
Last staff update: 9 January 2023 (update in progress)

Copyright: 2018-2019,, Inc.

PubMed Search: Squamous metaplasia of lactiferous ducts

Mary Ann G. Sanders, M.D., Ph.D.
Page views in 2022: 6,950
Page views in 2023 to date: 779
Cite this page: Sanders MAG. SMOLD. website. Accessed February 8th, 2023.
Definition / general
  • Ducts of nipple with keratinizing squamous metaplasia surrounded by a foreign body chronic active inflammatory response
Essential features
  • Clinical history of smoking and recurrent subareolar abscess is common
  • Presence of a single fistula tract at the areolar edge, if present, is characteristic
  • FNA will show anucleate squamous cells and keratin debris
  • Lactiferous duct lined by squamous epithelium and filled with keratin debris deep in the nipple and surrounded by a stromal mixed inflammatory infiltrate
  • Treatment is surgical excision of the affected duct
  • Also called recurrent subareolar abscess, periductal mastitis, Zuska disease
  • Rare
  • Women and men, wide age range
  • Strong association with smoking (J Am Coll Surg 2010;211:41)
  • Tobacco exposure or decreased level of vitamin A secondary to smoking may cause squamous metaplasia (Surgery 1995;118:775)
  • Keratin plug blocking lactiferous duct leads to duct rupture and inflammation
Clinical features
  • Painful erythematous subareolar mass (may be mistaken for infection) (Clin Radiol 2012;67:e42)
  • Clinically mistaken for recurrent abscess after multiple ineffective treatments with incision, drainage and antibiotics
  • Inverted nipple can be seen
  • Single fistula tract opening at the edge of the areola beneath the smooth muscle of the nipple is characteristic (the path of least resistance)
  • Can have bacterial superinfection with multiple surgical incisions and drainage
Radiology description
Case reports
Clinical images

Contributed by Nicolas Ajkay, M.D.

SMOLD with acute abscess

SMOLD with single fistula

Microscopic (histologic) description
  • Squamous epithelium extending beyond the normal transition point to ductal epithelium (normal transition point is superficial within the duct orifice, at about 1 - 2 mm from the skin surface) (South Med J 1977;70:935)
  • Duct spaces filled with keratin debris
    • Keratin debris can extend into duct spaces lined by normal ductal epithelium
  • Duct rupture and spillage of keratin debris in stroma incites an acute and chronic inflammatory response with giant cells surrounding ducts with squamous metaplasia (Surg Pathol Clin 2009;2:391)
  • May see keratin debris present within giant cells in stroma
Microscopic (histologic) images

Contributed by Mary Ann Gimenez Sanders, M.D., Ph.D.

Surface epithelium and SMOLD

Involved duct and SMOLD

Keratin debris

Lactiferous ducts of the nipple

SMOLD deep in nipple

Cytology description
  • Mature squamous cells, anucleate squamous cells, mixed inflammation including macrophages (Acta Cytol 2003;47:27)
Cytology images

Contributed by Mary Ann Gimenez Sanders, M.D., Ph.D.

SMOLD Pap smear

Negative stains
Differential diagnosis
  • Granulomatous mastitis:
    • Granulomatous inflammation centered on ducts and lobules deep in the breast
    • Peripheral location with multiple sinus tracts opening to skin
    • No squamous metaplasia
    • No association with smoking (J Am Coll Surg 2008;206:269)
  • Mammary duct ectasia:
    • Chronic inflammatory reaction to duct secretions released into surrounding stroma, not keratin
    • Weakened duct walls lead to rupture, not keratin plugs
    • No association with smoking
    • Older women (BMJ 1993;307:772)
  • Abscess due to infections:
    • Culture or special stains for microorganisms are positive
    • No squamous metaplasia or keratin debris in stroma
  • Epidermal inclusion cyst:
    • Keratin cysts, if present, are seen in the superficial dermis of the nipple skin, not present deep within the nipple and not continuous with lactiferous ducts
Board review style question #1
A 39 year old woman with no prior history of breast disease presents with a painful erythematous periareolar mass. Fine needle aspiration shows mature and anucleate squamous cells. What is recommended for this patient?

  1. Central excision to remove the nipple
  2. Course of antibiotics
  3. Incision and drainage
  4. Observation
  5. Stop smoking
Board review style answer #1
E. Stop smoking

Finding mature and anucleate squamous cells on FNA smears of a subareolar mass is diagnostic of SMOLD. Although the correct treatment is duct excision of the affected duct, the patient should also be counseled on smoking cessation to prevent future incidents of SMOLD involving remaining lactiferous ducts. Central excision to remove the nipple (answer A) would be overtreatment but observation (answer D) would be undertreatment. Antibiotics, incision and drainage (answers B and C) are ineffective in treating SMOLD.

Comment here

Reference: Squamous metaplasia of lactiferous ducts (SMOLD)
Board review style question #2
A 36 year old woman presents with an erythematous, painful subareolar mass. The patient undergoes incision and drainage and the specimen is sent to pathology (see image). It is noted in the clinical history that the patient is a smoker and has had recurrent subareolar abscess treated with I&D and antibiotics in the past. What is the best diagnosis?

  1. Abscess
  2. Granulomatous mastitis
  3. Inflammatory breast cancer
  4. Invasive ductal carcinoma with osteoclast-like giant cells
  5. Squamous metaplasia of lactiferous ducts (SMOLD)
Board review style answer #2
E. Squamous metaplasia of lactiferous ducts (SMOLD)

The image shows giant cells engulfing keratin debris in a background of acute and chronic inflammation. Even in the absence of identifying lactiferous ducts with squamous metaplasia in the I&D specimen, the history of recurrent subareolar abscess and smoking in conjunction with the presence of granulomatous inflammation and keratin debris indicates a diagnosis of SMOLD.

Treatment of an abscess (answer A) includes incision, drainage and antibiotics, which are ineffective in cases of SMOLD. Since the patient's diagnosis is SMOLD, duct excision is the best therapy. Keratin debris is not a feature of granulomatous mastitis (answer B). The image shows no evidence of dermal intralymphatic carcinoma to support a clinical diagnosis of inflammatory breast cancer (answer C) and shows no evidence of invasive ductal carcinoma (answer D).

Comment here

Reference: Squamous metaplasia of lactiferous ducts (SMOLD)
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