When an “Ectopic Pregnancy” Isn’t an Ectopic Pregnancy: A Rare Case of Primary Extrauterine Peritoneal Choriocarcinoma

OBGYN Clinical Update

Diagnostic Challenges in a Patient Presenting With Positive β-hCG and Adnexal Mass

Ectopic pregnancy remains one of the most common diagnoses in women presenting with pelvic pain, adnexal masses, and elevated β-hCG levels. However, rare malignant conditions can closely mimic its clinical presentation, creating significant diagnostic challenges.

A recent case report describes an exceptionally rare case of primary extrauterine peritoneal choriocarcinoma initially mistaken for an ectopic pregnancy. The report includes detailed ultrasound, MRI, intraoperative, and histopathologic findings, providing valuable insights for clinicians evaluating atypical pregnancies.

Case Summary

A reproductive-aged woman presented with:

• Positive serum β-hCG

• Pelvic pain

• Imaging findings suggestive of ectopic pregnancy

• No evidence of an intrauterine gestation

  
  

Initial evaluation raised strong suspicion for an ectopic pregnancy. However, further imaging and surgical exploration revealed a highly vascular peritoneal mass that was ultimately diagnosed as primary extrauterine peritoneal choriocarcinoma, an extremely uncommon form of gestational trophoblastic neoplasia (GTN).

Why This Case Is Unique

Choriocarcinoma most commonly develops within the uterus following:

• Molar pregnancy

• Miscarriage

• Ectopic pregnancy

• Term pregnancy

Primary development within the peritoneal cavity without an identifiable uterine primary lesion is exceptionally rare.

The rarity of the condition, combined with its ability to produce markedly elevated β-hCG levels, makes misdiagnosis highly possible during initial assessment.

Imaging Findings

Ultrasound

Initial sonographic findings demonstrated:

• Adnexal/peritoneal mass

• Hypervascular characteristics

• Absence of an intrauterine pregnancy

These findings closely resembled those expected in ectopic pregnancy.

MRI

MRI provided additional characterization of the lesion, demonstrating:

• A highly vascular extrauterine mass

• Hemorrhagic components

• Peritoneal involvement

• No convincing uterine primary tumor

The imaging findings increased suspicion for a neoplastic process rather than a typical ectopic gestation.

Surgical Findings

At surgery, clinicians identified:

• A hemorrhagic peritoneal mass

• No tubal ectopic pregnancy

• No obvious uterine lesion

• Significant vascularity consistent with trophoblastic disease

The unusual operative appearance prompted comprehensive pathologic evaluation.

Pathologic Diagnosis

Histopathologic examination confirmed:

Primary extrauterine peritoneal choriocarcinoma

Characteristic findings included:

• Cytotrophoblasts

• Syncytiotrophoblasts

• Extensive hemorrhage and necrosis

• Immunohistochemical features consistent with trophoblastic malignancy

  
  

The diagnosis established the lesion as a form of gestational trophoblastic neoplasia rather than ectopic pregnancy.

Clinical Pearls

🔹 Not every elevated β-hCG with an adnexal mass represents ectopic pregnancy.

🔹 Persistent or unusually high β-hCG levels that appear disproportionate to imaging findings should prompt consideration of trophoblastic neoplasia.

🔹 Hypervascular pelvic or peritoneal masses on Doppler imaging warrant careful evaluation before definitive treatment.

🔹 MRI can provide valuable information when ultrasound findings are atypical or inconclusive.

🔹 Surgical findings inconsistent with tubal ectopic pregnancy should trigger immediate reconsideration of the differential diagnosis.

Differential Diagnosis of Elevated β-hCG With Extrauterine Mass

When imaging findings are atypical, consider:

• Tubal ectopic pregnancy

• Heterotopic pregnancy

• Gestational trophoblastic neoplasia

• Choriocarcinoma

• Placental site trophoblastic tumor

• Epithelioid trophoblastic tumor

• β-hCG–secreting germ cell tumors

  
  

Why This Matters for Clinical Practice

Delayed diagnosis of choriocarcinoma can lead to:

• Significant hemorrhage

• Metastatic spread

• Increased treatment complexity

  
  

Fortunately, gestational choriocarcinoma is highly chemosensitive, and early recognition can result in excellent outcomes.

This case underscores the importance of maintaining a broad differential diagnosis when evaluating presumed ectopic pregnancies, particularly when imaging, β-hCG trends, or intraoperative findings are unusual.

Bottom Line

Primary extrauterine peritoneal choriocarcinoma is an exceptionally rare but important mimic of ectopic pregnancy. In patients with elevated β-hCG levels and atypical imaging findings, clinicians should consider gestational trophoblastic neoplasia as part of the differential diagnosis. Careful integration of ultrasound, MRI, surgical assessment, and pathology is essential to avoid diagnostic delay and initiate appropriate oncologic management.

Reference

Primary extrauterine peritoneal choriocarcinoma mistaken for ectopic pregnancy: A case report with ultrasound, MRI, surgical images. International Journal of Gynecology & Obstetrics, 2025.

This case provides an excellent reminder that atypical β-hCG patterns, hypervascular pelvic masses, and unexpected operative findings should prompt consideration of rare trophoblastic neoplasms in addition to ectopic pregnancy.