Nerve-adjacent endometriosis mimicking a suprapubic nerve sheath tumor: illustrative case

Conception and design: Wang, Letchuman, Suarez-Jew, Jacques. Acquisition of data: Wang, Letchuman, Caliskan, Pekmezci. Analysis and interpretation of data: Wang, Letchuman, Caliskan, Suarez-Jew, Jacques. Drafting the article: Wang, Letchuman, Caliskan, Jacques. Critically revising the article: Wang, Letchuman, Suarez-Jew, Pekmezci. Reviewed submitted version of manuscript: Wang, Suarez-Jew. Approved the final version of the manuscript on behalf of all authors: Wang. Administrative/technical/material support: Jacques.

Endometriosis is a common condition defined as the presence of endometrial tissue outside of the uterine cavity. Common symptoms include pelvic pain, dysmenorrhea, and infertility. Diagnosis is typically accomplished through direct visualization of lesions through open or laparoscopic surgery. The differential diagnosis of suprapubic or pubic symphysis masses also includes hernias, osteitis pubis changes, desmoids, and sarcoma. In comparison, nerve sheath tumors, such as schwannomas or neurofibromas, are typically benign tumors that arise from the nerve sheath and present with pain, paresthesia, or focal neurological deficits, depending on their location. Our patient did not have any reported chronic pelvic pain or dysmenorrhea and instead reported a bothersome mass overlying her right hip that was well circumscribed and enhancing on pelvic MRI. High levels of discomfort during fine-needle aspiration and significant discomfort to mild touch raised suspicion for involvement of a peripheral nerve. However, histopathological evaluation ultimately revealed a diagnosis of endometriosis, demonstrating its potential to masquerade as a neoplastic lesion, particularly when found in uncommon locations. The pathogenesis of endometriosis is somewhat multifactorial and unclear. Proposed theories include retrograde menstruation, lymphatic or vascular flow, or intestinal metaplasia. 8 Endometrial tissue is typically found within or around reproductive organs in the pelvic cavity; however, extrapelvic endometriosis involving the nerves is rare but documented. Examples include the sciatic nerve, 3 lumbar plexus, 6 and even cerebral tissue. 9 More broadly, it can also be found in other soft tissues and muscle such as the wrist or groin. 10 Treatment consists of both medical and surgical modalities. Medical therapies include nonsteroidal anti-inflammatory medications, oral contraceptives, gonadotropin-releasing hormone analogs, progestins, and danazol. 11 In this case of extrapelvic endometriosis with suspected nervous system involvement, surgery is recommended in patients with severe or worsening neurological symptoms. 6 One challenge with this diagnosis is the lack of any definitive study to diagnose endometriosis outside of surgery and histology. Even traditional intrapelvic endometriosis is a challenging and underdiagnosed condition with a mean diagnostic delay in the United States of approximately 11 years. 12 , 13 Extrapelvic endometriosis is generally thought to be significantly rarer but has also been speculated to be significantly underdiagnosed due to the lack of any noninvasive, routine test for it. 14 While noninvasive tests for endometriosis such as blood tests for growth factors or immune markers have been proposed, 15 , 16 at this time, these tests remain at an investigational stage. Endometriosis can present in atypical extrapelvic locations and mimic other pathologies, such as nerve sheath tumors. Clinicians should maintain some suspicion for atypical presentations of endometriosis, particularly in female patients of reproductive age. Diagnosis is typically dependent on surgical inspection and histology, highlighting the clinical need for less invasive tests and modalities to support this diagnosis.

Dr. Pekmezci reported stock ownership (past relationship within 36 months) in Ocugen outside the submitted work.

A 44-year-old nulligravid woman with no significant past medical history presented for evaluation of a palpable suprapubic mass. She noticed the mass over her right hip 1 year prior to presentation and noted that it had slowly grown since then. She reported that the mass had been bothersome, painful to light touch, but denied any radiating pain. She denied any associated symptoms such as redness, warmth, or any recent trauma to the area. She denied any weakness or numbness. There was no known family history of nerve tumors. There was no relation between this pain and her periods. Gynecologically, she denied any dysmenorrhea or chronic pelvic pain. She reported regular periods lasting for 5 days with heavy bleeding, with no change over the past year. MRI of the pelvis with and without contrast demonstrated a nonspecific 1.1-cm enhancing soft tissue lesion with possible peripheral nerve involvement ( Fig. 1 ). Fine-needle aspiration was attempted but did not result in sufficient cellularity to support any diagnosis. Notably, the patient reported significant discomfort during the biopsy, which in addition to her allodynia further raised concern for peripheral nerve involvement. Given the steadily increasing bothersome nature of the mass unrelated to periods, excision was planned. FIG. 1. A: Noncontrast T2-weighted axial MR image demonstrating an 11 × 10.5–mm mass ( circle ) overlying the right pubic symphysis. B: Contrast T1-weighted axial MR image redemonstrating the contrast-enhancing nature of the mass ( circle ). A: Noncontrast T2-weighted axial MR image demonstrating an 11 × 10.5–mm mass ( circle ) overlying the right pubic symphysis. B: Contrast T1-weighted axial MR image redemonstrating the contrast-enhancing nature of the mass ( circle ). The patient was placed supine, and the mass was located via ultrasound. Incision was performed over the mass, which was excised and noted to be a tan-brown, firm, mildly vascular, and homogeneous mass approximately 1.1 × 1.1 cm in size. The mass was sent to the pathology department for frozen section analysis. No peripheral nerve involvement was found, but the mass was theorized to be compressing nearby superficial sensory nerves, so the incision was closed, and the patient was discharged home the same day. Histological sections of the resected tissue showed benign endometrial glands surrounded by endometrial stroma embedded within connective tissue and muscle consistent with endometriosis ( Fig. 2 ). FIG. 2. A: Histological section of the resected mass showing endometrial glands and stroma embedded within the dense fibroconnective tissue and skeletal muscle. The endometrial glands are lined by ciliated pseudostratified columnar epithelium and contain luminal secretions. B: Immunohistochemical stain for CD10 highlighting the endometrial stromal cells. C: Estrogen receptor stain highlighting both endometrial glands and stroma. Original magnification ×5 (A–C). A: Histological section of the resected mass showing endometrial glands and stroma embedded within the dense fibroconnective tissue and skeletal muscle. The endometrial glands are lined by ciliated pseudostratified columnar epithelium and contain luminal secretions. B: Immunohistochemical stain for CD10 highlighting the endometrial stromal cells. C: Estrogen receptor stain highlighting both endometrial glands and stroma. Original magnification ×5 (A–C). As of 1 month postoperatively, the patient reported that the surgical site had healed well and that she no longer experiences pain on touching the site. She was ultimately diagnosed with stage 4 endometriosis due to multiorgan involvement of her endometriosis, including deep ovarian infiltration; however, she is not seeking any further endometriosis treatment as she no longer has any attributable bothersome symptoms. The necessary informed consent was obtained in this study.

Maxwell B. Wang: University of California, San Francisco, CA. [email protected] .