Endometriosis is a chronic, estrogen-dependent inflammatory condition characterized by the presence of endometrial-like tissue outside the uterus. While most cases involve the pelvic region—such as the ovaries, fallopian tubes, and peritoneum—extrapelvic endometriosis (EPE) accounts for approximately 12% of all endometriosis instances. This rarer form involves ectopic endometrial tissue in sites beyond the pelvis, including the gastrointestinal tract, urinary system, thoracic cavity, abdominal wall, and even more unusual locations like the liver, pancreas, spleen, and peripheral nerves. EPE often presents diagnostic challenges due to its atypical symptoms and variable locations, which can mimic other conditions such as malignancies, hernias, or inflammatory diseases. 

Unusual Presentations of Extrapelvic Endometriosis

Extrapelvic endometriosis can manifest in diverse sites, leading to a wide array of symptoms that are often cyclical and linked to the menstrual cycle. These presentations are influenced by the affected organ and the extent of infiltration. Common extrapelvic sites include the abdominal wall (often post-surgical scars), umbilicus, inguinal region, perineum, gastrointestinal tract (e.g., appendix and small intestine), liver, pancreas, kidneys, diaphragm, thoracic cavity, and peripheral nerves. Rare cases have been reported in the spleen, pericardium, and even the central nervous system.

Abdominal Wall and Scar Endometriosis

One of the most frequent extrapelvic sites is the abdominal wall, particularly in surgical scars following cesarean sections or other gynecological procedures (incidence ~0.8–3.5%). Patients typically present with a palpable, tender mass that swells and becomes painful during menses. Cyclic bleeding from the scar may occur, and the lesion can grow over time, mimicking suture granulomas, incisional hernias, or malignancies. Rare malignant transformations, such as clear cell carcinoma, have been noted.

Umbilical and Inguinal Endometriosis

Umbilical endometriosis (Villar’s nodule) is rare (0.5–1%) and often iatrogenic. It appears as a bluish-pink mass (up to 6 cm) that enlarges premenstrually and may bleed, earning the moniker "menstruating tumor." Inguinal endometriosis (~0.6%), usually right-sided, presents as a swelling mass during menses, often associated with hernias.

Gastrointestinal and Hepatic Involvement

Appendiceal endometriosis can cause acute appendicitis, intestinal obstruction, or gastrointestinal bleeding, mimicking diverticulitis or abscesses. Small intestine lesions (4.1–16.9%) lead to multifocal obstructions. Hepatic endometriosis (~22 reported cases) presents as cystic lesions mimicking abscesses or tumors, while pancreatic involvement may cause epigastric pain or pancreatitis.

Thoracic and Diaphragmatic Endometriosis

Diaphragmatic involvement (1–1.5%) often leads to catamenial pneumothorax, cyclical dyspnea, chest or shoulder pain, or hemoptysis. Thoracic lesions can extend to the pericardium, causing cyclic chest pain.

Other Rare Sites

Renal endometriosis (~10 cases) appears as nodules, while peripheral nerve involvement (e.g., sciatic nerve) causes neuropathic pain. Splenic cases present with cyclic left upper quadrant pain, dyspnea, bloating, and anemia, sometimes requiring splenectomy. Retroperitoneal cysts posterior to the pancreas may cause epigastric pain, nausea, and vomiting.

These atypical presentations underscore the need for a high index of suspicion, especially in reproductive-age women with cyclical symptoms and a history of pelvic surgery.

Diagnostic Criteria for Extrapelvic Endometriosis

Diagnosis of EPE relies on a multifaceted approach, as no single test is definitive. The gold standard remains laparoscopic visualization with histopathological confirmation, requiring the presence of endometrial epithelium, glands, stroma, and/or hemosiderin-laden macrophages. However, to minimize delays, nonsurgical diagnosis is increasingly emphasized based on symptoms, examination, and imaging.

Clinical History and Examination

A detailed history should assess for cyclical pain (e.g., dysmenorrhea, dyspareunia, dyschezia), infertility, prior surgeries, and atypical symptoms like hematuria or pneumothorax. Pain scales (VAS/NRS) help quantify severity. Physical examination may reveal tender masses, nodules, or organ-specific signs, though it can be normal in mild cases.

Imaging and Invasive Diagnostics

Imaging aids in mapping lesions and ruling out differentials. MRI is useful for deep or extrapelvic sites, while cystoscopy, sigmoidoscopy, or ultrasound-guided fine needle aspiration (FNA) may be employed for specific locations (e.g., bladder, bowel, scars). Histopathology confirms the diagnosis, but laparoscopic inspection alone has limitations, with only 54–67% of suspected lesions verified.

The Role of Ultrasound in Diagnosis

Ultrasound serves as a first-line, accessible, and cost-effective imaging modality for endometriosis, with high accuracy for detecting ovarian endometriomas and deep lesions. Transvaginal ultrasound (TVU) is preferred for pelvic assessment, achieving sensitivity and specificity >90% for deep endometriosis when performed by experts. Transabdominal ultrasound (using linear probes, 5–13 MHz) is valuable for superficial extrapelvic sites like the abdominal wall.

Sonographic Features

Lesions often appear as hypoechoic nodules or masses with irregular/spiculated margins, hyperechoic spots (fibrosis), ground-glass echogenicity, and peripheral vascularization on Doppler. For example:

-Abdominal Wall/Scar: Hypoechoic solid nodules with spiculated borders; larger lesions (>30 mm) may show cystic components.

-Umbilical: Solid or partially cystic with ill-defined margins and no fascial continuity.

-Diaphragmatic: Hypoechoic lesions or hyperechoic foci along the diaphragmatic line.

-Hepatic/Pancreatic: Small hypoechoic lesions.

Advanced techniques, such as 3D ultrasound, assess lesion volume, depth, and infiltration, aiding surgical planning. Ultrasound guides biopsies and differentiates from mimics, but it cannot detect superficial peritoneal implants or adhesions reliably. For inconclusive cases, MRI is recommended as a complementary tool.

In extrapelvic sites, ultrasound's role is fundamental when typical cyclical symptoms are present, offering a non-invasive means to identify and characterize lesions.

Extrapelvic endometriosis, though uncommon, presents with diverse and often misleading symptoms that demand clinical vigilance. Diagnostic criteria emphasize integrating history, examination, and imaging, with ultrasound playing a central role due to its accessibility and diagnostic precision in atypical sites. Early recognition through multimodal approaches can improve outcomes, reducing the burden of this enigmatic condition. Further research is needed to refine diagnostic tools and understand EPE's pathogenesis.

November 2025