Testis and epididymis
Germ cell tumors
Yolk sac tumor

Topic Completed: 1 January 2013

Revised: 28 March 2019

Copyright: 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Testis yolk sac tumor [title]

Turki Al-Hussain, M.D.
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Cite this page: Al-Hussain T. Yolk sac tumor. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/testisyst.html. Accessed September 23rd, 2019.
Definition / general
  • Also called endodermal sinus tumor of Teilum (endoderm is embryonic layer closest to yolk sac)
  • Numerous patterns that recapitulate the yolk sac, allantois and extra-embryonic mesenchyme
  • Most common testicular tumor age 3 or less; often pure; good prognosis at this age (80%+ are stage I)
  • Adults: usually part of a mixed tumor, has prognosis of embryonal carcinoma
  • 95%+ of patients with tumors containing yolk sac elements have elevated serum AFP although some children have physiologic elevations of AFP without yolk sac tumors
  • Tumors usually aneuploid
  • After treatment, may give rise to spindle cell sarcoma with myxoid or collagenous stroma
  • May arise from seminoma in some cases (Am J Clin Pathol 1992;97:468)
  • AFP: major serum protein of early fetus, produced by fetal gut, hepatocytes, yolk sac
Gross description
  • Nonencapsulated, homogenous, yellow white, mucinous, soft, multicystic
  • Adult cases often have hemorrhage and necrosis, 2 - 6 cm
Microscopic (histologic) description
  • Lace-like (reticular), papillary or cord-like pattern of cuboidal / elongated cells
  • Also other patterns (see below)
  • Cells have bland nuclei
  • 50% of tumors have Schiller-Duval bodies (also called endodermal sinuses, with central capillary and visceral and parietal layer of cells resembling primitive glomeruli)
  • Tumor cells have eosinophilic hyaline globules (within and outside cytoplasm) that are alpha-1 antitrypsin+ and PAS diastase+; uncommon in seminoma and embryonal carcinoma
  • Intratubular germ cell neoplasia not present in young patients (Arch Pathol Lab Med 1988;112:641), often present after puberty
  • Yolk sac is most commonly overlooked component of NSGCT so take adequate sections (Hum Pathol 1978;9:553)

Eleven microscopic patterns:

Endodermal sinus (perivascular, festoon):
  • Predominance of Schiller-Duval bodies, plus fibrous cores of tissue draped (festooned) by tumor cells or spaces

Glandular - alveolar:
  • Primitive glands with apical brush border, resembling GI epithelium
  • Glands may develop from cystic alveolar-like spaces
  • Resemble teratomas but AFP+ and no circumferential smooth muscle

  • Clusters of polygonal cells with eosinophilic cytoplasm, round nuclei, prominent nucleoli, arranged in trabecular, nested or sheet-like patterns
  • Intensely positive for AFP

  • Large cysts result from coalescence of microcysts

  • Cells in thin cords or trabeculae in mucoid stroma
  • Occasionally form skeletal muscle and cartilage (some call yolk sac tumor with rhabdomyoblastic differentiation)

  • Fibrous papillary cores or papillary epithelium projecting into cystic spaces
  • Cells have high nuclear/cytoplasmic ratios, hobnail configuration

  • Predominance of basement membrane between tumor cells (parietal layer of embryonic yolk sac produces a thick basement membrane)
  • Present in 90%+ yolk sac tumors
  • Focal wispy to band like deposits of eosinophilic matrix
  • Usually with other patterns

Polyvesicular vitelline:
  • Irregular vesicles lined by flat, cuboidal or columnar cells
  • Vacuoles often present

Reticular or microcystic:
  • Most common
  • Microcystic or honeycomb or lace-like pattern
  • Cells may resemble lipoblasts or signet ring cells

  • Proliferation of spindle cells associated with myxomatous pattern
  • Cytokeratin+

  • Sheet like cells that resemble seminoma but without fibrous stroma and lymphocytes
  • Microcystic areas and other typical yolk sac patterns usually present
  • Cytokeratin+ (seminomas are negative)
  • May have blastema-like cells (small, primitive)
Microscopic (histologic) images

Images hosted on PathOut server:

Images contributed by Dr. Asmaa Gaber Abdou, Menofiya University, Egypt:

Metastatic to abdomen

Images hosted on other servers:

Endodermal sinus (perivascular, festoon)


Reticular or microcystic



Positive stains
Negative stains
Electron microscopy description
  • Epithelial cells with tight junctional complexes, apical microvilli, extracellular deposits of basal lamina, glycogen
  • Note: AFP also found in embryonal carcinomas, teratocarcinomas, tumors without microscopic yolk sac elements and hepatocellular carcinoma
Differential diagnosis
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