Table of ContentsDefinition / general | Essential features | Clinical features | Diagnosis | Radiology description | Case reports | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Positive stains | Board review question #1 | Board review answer #1 | Board review question #2 | Board review answer #2
Cite this page: Garg, S. Metastases. PathologyOutlines.com website. http://pathologyoutlines.com/topic/placentamets.html. Accessed November 21st, 2017.
Definition / general
- Metastatic involvement of placenta by maternal or fetal tumors
- Placental metastases during pregnancy affect about 0.1% of pregnant women and most of them are of maternal origin, rarely of fetal origin
- Infrequent occurrence of this condition suggests that biological protective mechanisms may exist for the placento - fetal unit
- In the absence of gross metastases, meticulous microscopic examination may reveal a higher incidence of placental metastases
- Most common metastatic maternal tumors are melanoma (30%) (Singapore Med J 2008;49:e71), breast carcinoma (14%), leukemia and lymphoma (15%), small cell carcinoma of lung (N Engl J Med 2002;346:1501) and gastric carcinoma (Oncol Lett 2014;8:2509)
- Metastatic fetal tumors are very rare and include neuroblastoma (Int J Clin Exp Pathol 2014;7:8198), adenoid cystic carcinoma of trachea (Hum Pathol 1989;20:193), hepatoblastoma, melanoma and rhabdoid tumor
- Fetal and maternal circulation is separated by trophoblast, connective tissue of the villus and the capillary wall; only when the tumor cells from the intervillous space invade into the villous capillaries can the metastases to fetus occur (Cancer 1970;25:380)
- Placental abruption with disseminated intravascular coagulation and fetal death can occur due to placental metastases in the intervillous space
- When placental metastases are present but with no villous invasion, the risk of fetal metastases may be extremely low, even in the setting of aggressive, terminal malignancy in the mother
- Rarely, the mother may suffer from antepartum effects, such as sweating, flushing, palpitations and hypertension due to production of catecholamine by the neuroblastoma
- By meticulous histologic examination of the placenta in suspicious cases
- Nonspecific increased placental thickness
- Placenta may appear bulky, pale and heavy, while tumor deposits are usually not macroscopically detectable (being identified mostly on histologic examination)
Microscopic (histologic) description
- Multifocal clusters of malignant cells adjacent to intact villi
- Metastases from maternal melanoma may show infiltration of villous stroma by malignant cells with Hofbauer cells containing melanin, even in the absence of villous invasion
- Most cases of placental involvement are associated with minimal fetal complications but massive placental infiltration by maternal metastasis can lead to intrauterine fetal death (IUFD)
- Presence of malignant cells in the intervillous space has been classified as placental metastasis although in reality the tumor cells remain within the maternal vascular space and in most cases do not truly invade placental tissue
- Maternal leukemia with circulating malignant hematopoietic cells is associated with similar cells admixed within the intervillous space without true invasion (Ultrasound Obstet Gynecol 2009;33:235)
- Stains specific for the primary maternal or fetal malignancy
Board review question #1
When is the risk of fetal metastasis by a maternal malignant tumor highest during pregnancy?
- When the placenta has choriocarcinoma
- When the tumor cells are present in the chorionic membranes
- When the tumor cells are seen in the intervillous space
- When the tumor cells invade into the chorionic villi
Board review answer #1
D. When the tumor cells invade into the chorionic villi.
Board review question #2
Which maternal and fetal tumors have been shown to have the highest risk of placental metastases?
- Breast carcinoma and adenoid cystic carcinoma
- Gastric carcinoma and hepatoblastoma
- Leukemia and rhabdoid tumor
- Melanoma and neuroblastoma
Board review answer #2
D. Melanoma and neuroblastoma.