Table of Contents
Definition / general | Clinical features | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Positive stains | Negative stains | Differential diagnosis | Board review style question #1 | Board review style answer #1Cite this page: Lanjewar S, Gupta R. Placental site nodule. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/placentaplacentalsitenodule.html. Accessed January 23rd, 2021.
Definition / general
- Placental site nodules (or plaques) are small and well circumscribed nodular aggregates of intermediate trophoblastic cells embedded in a hyalinized stroma
- Represent the benign counterpart of the epithelioid trophoblastic tumor
- Atypical placental site nodule (ASN) is a term assigned to placental site nodules with significant nuclear atypia and/or borderline proliferation index (see below)
Clinical features
- Discovered incidentally in uterine or endocervical curettings, cervical biopsies and rarely in hysterectomy specimens
- Placental site nodules have been detected in fallopian tubes, presumably a consequence of prior tubal pregnancy (Int J Gynecol Pathol 2003;22:362, Int J Gynecol Pathol 1997;16:219)
- Due to small size and circumscription, these lesions are usually completely surgically excised by curettage
- These lesions are not known to recur or progress to persistent gestational trophoblastic disease (Int J Gynecol Pathol 2001;20:31)
- No specific treatment or follow up is necessary for this lesion
- The behavior of atypical placental site nodule has not yet been studied
Gross description
- Placental site nodules are small lesions, from 1 to 14 mm (average 2.1 mm)
- Grossly, these appear as a yellow, white and necrotic appearing nodule in the endometrium or superficial myometrium
Microscopic (histologic) description
- Small nodular or plaque-like lesions with rounded, well circumscribed borders which are surrounded by chronic inflammatory cells and occasionally decidualized stroma
- Nodules typically are composed of haphazardly arranged extravillous trophoblast
- Most trophoblast cells are of "immature (epithelioid) extravillous” type (p63+, CD146-); a minor component of "mature extravillous” type trophoblast (p63-, CD146+) can be seen (Mod Pathol. 2017;30(2s):301A [abstract #1210])
- Trophoblast is usually distributed in the outer portion of nodule around a central hyalinized extracellular matrix
- Mitotic figures are absent or rare
- Cells vary in size and have relatively small uniform nuclei
- Cytoplasm of the larger trophoblastic cells is abundant and eosinophilic; the smaller cells contain glycogen rich clear cytoplasm (Kurman: Blaustein's Pathology of the Female Genital Tract, 6th Edition, 2011)
- Ki67 proliferation index is low (< 8%)
- Atypical placental site nodules: placental site nodule with moderate to severe atypia and Ki67 proliferation index 8 - 10% (Kurman: WHO Classification of Tumours of the Female Reproductive Organs, 4th Edition, 2014)
- These lesions may represent a transition from benign placental site nodule to epithelioid trophoblastic tumor (Int J Gynecol Pathol 2015;34:152)
Microscopic (histologic) images
Positive stains
Differential diagnosis
- Epithelioid trophoblastic tumor (ETT)
- These are larger lesions, more cellular, have extensive necrosis and evident mitoses
- Calcifications are typically present in ETTs and when present, lesion is more likely to be an ETT than placental site nodule
- Cyclin E is expressed in ETT and absent in placental site nodule
- Ki67 index is high (> 10%)
- Squamous cell carcinoma of the cervix
- Circumscription, abundant eosinophilic extracellular deposit and lack of mitotic activity favor a placental site nodule
- Placental site nodules are typically negative for p16
Board review style question #1
The typical immunophenotypic profile of placental site nodule is:
- p63-, hPL-, cyclin E+
- p63-, hPL+, cyclin E-
- p63-, hPL+, cyclin E+
- p63+, hPL+, cyclin E-
Board review style answer #1