Placental site trophoblastic tumour: the rarest subtype of gestational trophoblastic disease

Abstract

Placental site trophoblastic tumour (PSTT) is a very rare form of gestational trophoblastic disease that grows slowly, secretes low levels of beta-subunit of human chorionic gonadotropin (β-hCG), presents late-onset metastatic potential and is resistant to several chemotherapy regimens. Here, we report a case of PSTT in a 36-year-old woman who presented with amenorrhea and persistently elevated serum level of β-hCG after a miscarriage. Transvaginal ultrasound revealed a hypovascular ill-defined solid lesion of the uterine fundus and MRI showed a tumour infiltrating the external myometrium with discrete early enhancement and signal restriction on diffusion-weighted imaging. PSTT was suspected, and after endometrial biopsy by hysteroscopy and posterior hysterectomy, microscopic examination allowed the final diagnosis. The level of β-hCG dropped significantly in about a month after surgical treatment. Due to the rarity of PSTT, reporting new cases is crucial to improve the diagnosis and managing of these patients.

Keywords: gynecological cancer; pathology; radiology.

Figure 1

(A) Transvaginal sonography with a 10 MHz endocavitary probe (midline axial view) shows an ill-defined solid tumour on the left wall of the uterine fundus (white arrows). (B) Transvaginal ultrasound with colour Doppler (midline sagittal view) demonstrates minimal blood flow of the lesion.

Figure 2

(A) Sagittal T2-weighted image reveals a solid tumour in the uterine fundus and infiltrating the external myometrium (white arrow). (B) Axial oblique (perpendicular to the long axis of endometrial cavity) T2-weighted image shows that the tumour was slightly hyperintense on T2 (white arrow) comparing to the uterine myometrium (yellow arrow). (C) Axial oblique T1-weighted image with fat suppression, obtained 25 s after contrast medium injection, demonstrates early tumour enhancement (white arrow). (Philips Intera Pulsar 1.5T: T2-weighted sagittal image (Repetition time (TR)=3825; Echo time (TE)=100); T2-weighted axial image (TR=3684; TE=105); dynamic contrast-enhanced MRI obtained with a T1-weighted sequence (TR=5.76; TE=2.79), with fat suppression and after the administration of 0.1 mmol/kg of gadopentetate dimeglumine at a rate of 2 mL/s.)

Figure 3

(A) In the axial diffusion-weighted MRI, the tumour shows high signal intensity. (B) In the axial apparent diffusion coefficient map, the area of high signal intensity in the diffusion-weighted MRI shows low signal intensity, a finding that is consistent with restricted diffusion. (Philips Intera Pulsar 1.5T: axial diffusion-weighted images (TR=2616; TE=72.1); Flip angles of 90^o, performed with b values of 1000 s/mm².)

Figure 4

Highly cellular proliferation with predominance of intermediate trophoblast cells and scattered syncytiotrophoblast cells (arrows). Ectatic vessels (*) in an otherwise poorly vascular tumour. Inset: further cytologic detail of the lesional cells and spiral endometrial artery (**) (low magnification image).

Figure 5

(A) Beta-subunit of human chorionic gonadotropin production by scattered cells (arrows), confirming their syncytiotrophoblastic nature. (B) Low Ki67 (estimated between 5% and 10%), in contrast to the usually higher than 10% proliferation fraction of epithelioid trophoblastic tumours and very high proliferation fraction of choriocarcinomas (typically >90%) (medium magnification images).

Figure 6

(A) Fleshy homogeneous lesion situated around the endometrial cavity; (B) expansive, well-demarcated growth of the lesion within the myometrium.