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| LETTER |
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| Year : 2014 | Volume
: 60
| Issue : 2 | Page : 214-216 |
A rare microscopic finding in an early abortion specimen
MY Leong, M Gudi, TE Chang, C Kwan
Department of Pathology and Laboratory Medicine, KandangKerbau Women's and Children's Hospital, Singapore
| Date of Web Publication | 13-May-2014 |
Correspondence Address:
Dr. M Y Leong
Department of Pathology and Laboratory Medicine, KandangKerbau Women's and Children's Hospital
Singapore
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0022-3859.132375
How to cite this article:
Leong M Y, Gudi M, Chang T E, Kwan C. A rare microscopic finding in an early abortion specimen. J Postgrad Med 2014;60:214-6 |
Sir,
We present in this letter the histological features of yolk sac in early abortion. The product of conception from a first trimester complete miscarriage showed various fetal tissue including liver, neuroepithelium, and immature mesenchyme, chorionic villi, decidua, and a structure reminiscent of a collapsed sac. This structure was composed of three layers. The sac was lined by cohesive large polygonal cells forming tubular structures. The outer surface was lined by a single layer of flat to low cuboidal cells. There was loose, reticular mesenchymal tissue with blood vessels containing nucleated red cells between the two layers. [Figure 1] and [Figure 2] The inner polygonal cells demonstrated mild cellular atypia with occasional cells showing irregular nuclear outline, prominent, and multiple nucleoli [Figure 3]. Immunohistochemistry showed this structure was nonreactive for α-inhibin and reactive for α-fetoprotein confirming its nature as an early yolk sac [Figure 4]. | Figure 1: Histology shows fetal tissue, chorionic villi, and yolk sac (HandE, originalmagnification ×20)
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 | Figure 2: Cohesive polygonal cells focally form gland-like structure in a loose, reticular stroma. There are vessels containing nucleated erythroblasts (H and E, original magnification ×400)
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 | Figure 3: The polygonal cells show some cellular atypia with irregular nucleus, prominent and multiple nucleoli, and coarse chromatin (asterisk) (H and E, original magnification ×400)
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 | Figure 4:Immunohistochemical staining for alpha-fetoprotein highlights the yolk sac structure (Alpha-fetoprotein, original magnification ×100)
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In the 2 nd week of development, the bilaminar germ disc is sandwiched between two fluid-filledcavities: The amniotic cavity lined by amnioblasts derived from the epiblasts and the primary yolk sac lined by the migrating hypoblasts. [1] A loose, reticular acellular material deposited underneath the lining cells of the primary yolk sac contains a distinct population of extra embryonic mesodermal cells. The formation of a secondary yolk sac starts around day 12 of development as the second wave of hypoblast proliferation pushes aside the primary yolk sac towards the abembryonic pole which then detaches from the embryo and disintegrates into a transient collection of vesicles. The secondary yolk sac is the site of hematopoiesis, primordial germ cell differentiation, synthesis of serum proteins, and nutrient exchange during the early embryo life. As the embryo bends in subsequent weeks of development, the secondary yolk sac is divided into an intraembryonic part (the gut) and the extraembryonicpart (omphalomesenteric duct). [1] The extraembryonic part of the secondary yolk sac atrophies during development and usually disappears before birth.
Remnant of yolk sac can on occasions be seen in term placentas as a small, round, white to yellow plaque between the amnion and chorion with a histological appearance of an irregular, deeply basophilic, amorphous focus. Less frequently, yolk sac is seen in product of conception in early abortion and may be mistaken for other structures. [2] Yolk sac in these early abortion specimens is composed of three layers: The inner endodermal cells, the outer mesothelial cells and the middle lacy, reticularmesenchymal tissue. [2],[3] The endodermal cells are large cuboidal or columnar cells with round nuclei and distinct nucleoli. The mesodermal cells are flat or cuboidal and smaller than the endodermal cells.The blood vessels in the mesenchymal layer contain numerous-nucleated red cells. [3]
The early yolk sac, a normal feature in early gestation, is t an infrequent encounter in routine surgical practice. Awareness of the microscopic appearance of early yolk sac would prevent confusion with other structures and neoplasms particularly of trophoblastic derivation.
| :: References | |  |
| 1. | Larsen W. Human embryology. 3 rd ed. London:Churchill Livingstone; 2001. p. 38-43. 
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| 2. | Benirschke K, Burton GJ, Baergen RN. Pathology of the human placenta. 6 th ed. New York: Springer; 2012. p. 389-91,774-5.
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| 3. | Ukeshima A, Hayashi Y, Fujimoto T. Surface morphology of the human yolk sac: Endoderm and mesothelium. Arch HistolJpn 1986;49:483-94.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
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