Table of Contents
Extramedullary hematopoiesis | Megakaryocytes | Nevus cells | Squamous epithelium | ThymusCite this page: DePond W. Other ectopic tissue / inclusions. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/lymphnodesotherectopic.html. Accessed January 26th, 2023.
Extramedullary hematopoiesis
Definition / general
- Rarely associated with myeloproliferative disorders but also in healthy patients (Diagn Cytopathol 1993;9:522, Arch Otolaryngol 1982;108:523)
Microscopic (histologic) images
Contributed by Nikhil Sangle, M.D.
Liver with extramedullary hematopoiesis
Differential diagnosis
Megakaryocytes
Definition / general
- Often associated with extramedullary hematopoiesis when present in lymph nodes
Case reports
- 35 year old woman with megakaryocytes mimicking metastatic breast carcinoma (Arch Pathol Lab Med 2002;126:618)
Microscopic (histologic) images
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Megakaryocytes in bone marrow
Positive stains
Negative stains
Differential diagnosis
- Multinucleated histiocytes:
- Larger, more cytoplasm, vesicular nuclei that are not multilobated
- CD68+
Nevus cells
Definition / general
- Incidence in axillary nodes is 7% per patient and 0.5% per node in one study (Am J Clin Pathol 1994;102:102)
- Presence in sentinel nodes in melanoma patients is associated with
- Cutaneous nevi (Am J Clin Pathol 2004;121:58)
- Congenital cutaneous nevi (Am J Dermatopathol 2002;24:1)
- May represent benign metastases from intradermal nevus in area of lymphatic drainage (Am J Clin Pathol 1985;84:220)
Microscopic (histologic) description
- Single cells, linear arrangements or aggregates of small, round / oval nevus cells with moderate pale / clear cytoplasm, round nuclei with fine chromatin, no prominent nucleoli or pleomorphism, usually within fibrous capsule and trabeculae but also within nodal parenchyma or surrounding a small vessel (Am J Surg Pathol 2003;27:673, Am J Surg Pathol 1996;20:834)
Microscopic (histologic) images
Contributed by Debra L. Zynger, M.D.
Nests within capsule
Bland cells
SOX10
S100
AE1/3
Positive stains
Negative stains
- HMB45 (occasionally is very focal), Ki-67 (< 1%, Am J Surg Pathol 2002;26:1351)
Differential diagnosis
- Blue nevus:
- Also spindled / dendritic cells with heavy pigmentation
- Metastatic carcinoma or melanoma:
- Usually not confined to capsule, atypia, mitotic figures, different immunostaining
- Spitz nevus:
- Larger cells with abundant eosinophilic cytoplasm
- Vesicular nuclei with prominent nucleoli
Squamous epithelium
Definition / general
- Also called lymphoepithelial cyst
- Most common in upper cervical nodes
- Depending on location, may be a branchial pouch derivative or derive from metaplastic calyceal urothelium (Hum Pathol 1990;21:1239)
Case reports
- 33 and 64 year old women with benign heterotopic epithelial inclusions in axillary lymph nodes (Arch Pathol Lab Med 2003;127:e25)
- 48 year old woman with axillary intranodal cysts associated with breast malignancy (Arch Pathol Lab Med 2004;128:361)
- 57 and 75 year old women with cystic lymphoepithelial lesions of peripancreatic nodes (Surg Today 1999;29:467)
- Epithelial inclusion in axillary lymph node associated with a breast carcinoma (Pathol Res Pract 1999;195:263)
Microscopic (histologic) description
- Small cystic structures lined by well differentiated squamous epithelium
Differential diagnosis
- Metastatic well differentiated squamous cell carcinoma:
- Often undergoes cystic change
