Lymph nodes & spleen, nonlymphoma

Ectopic tissue / inclusions

Smooth muscle

Last author update: 1 September 2014
Last staff update: 18 July 2022

Copyright: 2003-2023,, Inc.

PubMed Search: Smooth muscle [title] lymph nodes

Jayalakshmi Balakrishna, M.D.
Page views in 2022: 873
Page views in 2023 to date: 75
Cite this page: Balakrishna J. Smooth muscle. website. Accessed January 26th, 2023.
Definition / general
  • Topic discusses the presence of smooth muscle within the capsule and hilum of normal lymph nodes
  • Common, incidental finding in lymph nodes of hilar smooth muscle proliferation, more commonly in males than females (Virchows Arch A Pathol Anat Histopathol 1985;406:261)
  • Superficial, inguinal and axillary lymph nodes are most commonly involved
  • Suggested etiological factors include back pressure in efferent lymphatics, local inflammation
Clinical features
  • Asymptomatic, with no apparent clinical significance, but may have enlarged lymph nodes
  • Biopsy
  • Immunohistochemistry for smooth muscle to confirm
Case reports
Gross description
  • Enlarged lymph nodes with firm, tan cut surface
Microscopic (histologic) description
  • Nodal architecture is well preserved
  • Muscle fibers run parallel to capsule or hilar blood vessels
  • Varied patterns of hilar changes:
    • Smooth muscle fibers may be densely interwoven within fibrous tissue and hug the hilar nodal capsule
    • Smooth muscle fibers may form a loose network extending in all directions within hilar adipose tissue
    • Smooth muscle may surround individual islands of fat cells
Microscopic (histologic) images

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Angiomyomatous hamartoma of lymph node

Negative stains
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