Placental site trophoblastic tumor

Last revised by Joshua Yap on 10 May 2023

Placental site trophoblastic tumors (PSTT) are rare and one of the least common (~0.2% 7) forms of gestational trophoblastic disease.

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Placental site trophoblastic tumors typically occur in women of reproductive age with an average age of ~30 years. They may occur after a normal pregnancy, molar pregnancy, or even after a terminated pregnancy. 

Patients can present anywhere between 1 week and 14 years. Presenting symptoms can include either abnormal vaginal bleeding or amenorrhea 6. Up to 30% of patients may present with metastases at the time of diagnosis 10. 

A placental site trophoblastic tumor is composed of neoplastic transformation of intermediate trophoblastic cells that form a polypoid mass that may be within the endometrial canal or the myometrium.

It may be divided into two main types depending on vascularity 4:

  • hypervascular

  • relatively hypovascular

There can be some imaging overlap with an invasive mole and choriocarcinoma. One of the key roles of imaging is to attempt to clarify the vascularity of a tumor.

Transvaginal ultrasonographic features of placental site trophoblastic tumors are classified into three types depending on the location (within the uterine cavity or the myometrium) and the characteristics (solid or cystic tissue) of the lesion: 

  • type 1: heterogeneous solid mass located in the uterine cavity, with minimal to a moderate degree of vascularization on color Doppler imaging

  • type 2: heterogeneous solid mass within the myometrium (invasion ≥50% of its thickness), with minimal to a high degree of vascularization on color Doppler imaging

  • type 3: cystic lesions within the myometrium, with a high degree of vascularization (lacunar-type lesions), indicating an arterio-venous shunt

The lesions are of varying sizes with ill-defined borders within the uterus (maximum diameter of the masses is 2-6 cm, with a mean mass diameter of 3 cm) ref.

Color Doppler exploration is performed to evaluate blood flow within the mass (in the center or at the border of tumors) and the degree of vascularization which is subjectively classified as:

  • minimal: <5 points of Doppler flow signal

  • moderate: ≥5 points of Doppler flow signal or a single branching vessel

  • high: multiple focal vessels

Doppler waveform analysis of vessels within the placental site trophoblastic tumor typically demonstrates high-velocity flow and low impedance ref.

A placental site trophoblastic tumor may present as a heterogenous endometrial and myometrial mass although appearances on MRI can be non-specific. The junctional zone is disrupted. In the majority of cases, there are cystic spaces and vascular structures.

Reported signal characteristics include 1,3:

  • T1: typically isointense compared with healthy myometrium

  • T2: isointense to slightly hyperintense compared with myometrium

A hysterectomy is the primary mode of treatment in the majority of cases 7. A tumor tends to remain confined to the uterus until late in its course although can eventually metastasize to the lung, liver, lymph nodes, and brain. Metastases can occur many years after the initial diagnosis 3.

Their biological behavior is variable, ranging from benign lesions confined to the uterus to highly aggressive malignant disease with systemic metastases. The main negative prognostic variables are the time to presentation from the last known pregnancy and the mitotic index.

While there can be a good prognosis with localized disease, the tumors tend to be less sensitive to chemotherapy than other forms of gestational trophoblastic disease 6. However, chemotherapy may still play a role with lesions that are not amenable to curative surgery 7. 

It was first described by R J Kurman et al. in 1976 as a "trophoblastic pseudo-tumor". The term "placental site trophoblastic tumor" was later coined by R E Scully and R H Young in 1981 5.

For MRI appearances consider:

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