Isolated perineal endometriosis? Yes ... an exceptional location

We present a case of a 40-year-old woman who had no previous history of endometriosis but underwent 1 vaginal delivery (G1P1) with an episiotomy on the left side. The patient's chief complaint is a left perineal tumor that enlarges and becomes painful during menstruation, with no signs of inflammation. During the clinical examination, a tumor in the left perineal area was identified, showing no signs of inflammation, fistulous tract, or pus. An initial MRI was conducted, revealing the following findings: • A well-defined, rounded cystic lesion in the left perineum, showing hypersignal on T1 and FAT SAT sequences ( Fig. 1 ), intermediate T2 signal (decreased signal intensity) without visible nodules or partitions within the cyst. The lesion was pushing against the postero-lateral wall of the vagina in its distal third ( Figs. 2 A and B) and showed a restrictive signal on the DWI sequence ( Fig. 3 ). Fig. 1 The image displays a perineal lesion with T1FATSAT hypersignal, indicating an endometriotic cyst (White arrow). Fig 1: Fig. 2 Both the axial T2-weighted sequence (A) and the Coronal T2-weighted sequence (B) reveal a left cystic perineal lesion with intermediate signal T2 (shading compared to the T1 sequence - black arrow), closely approaching the postero-lateral wall of the distal third of the vagina (yellow arrow). Fig 2: Fig. 3 The diffusion sequence demonstrates restricted diffusion within the left perineal endometriotic cystic lesion (Blue arrow). Fig 3: • The uterine transitional zone appeared thin with no signs of adenomyosis. • Uterine ligaments and the ureter showed no abnormalities. A well-defined, rounded cystic lesion in the left perineum, showing hypersignal on T1 and FAT SAT sequences ( Fig. 1 ), intermediate T2 signal (decreased signal intensity) without visible nodules or partitions within the cyst. The lesion was pushing against the postero-lateral wall of the vagina in its distal third ( Figs. 2 A and B) and showed a restrictive signal on the DWI sequence ( Fig. 3 ). Fig. 1 The image displays a perineal lesion with T1FATSAT hypersignal, indicating an endometriotic cyst (White arrow). Fig 1: Fig. 2 Both the axial T2-weighted sequence (A) and the Coronal T2-weighted sequence (B) reveal a left cystic perineal lesion with intermediate signal T2 (shading compared to the T1 sequence - black arrow), closely approaching the postero-lateral wall of the distal third of the vagina (yellow arrow). Fig 2: Fig. 3 The diffusion sequence demonstrates restricted diffusion within the left perineal endometriotic cystic lesion (Blue arrow). Fig 3: The image displays a perineal lesion with T1FATSAT hypersignal, indicating an endometriotic cyst (White arrow). Both the axial T2-weighted sequence (A) and the Coronal T2-weighted sequence (B) reveal a left cystic perineal lesion with intermediate signal T2 (shading compared to the T1 sequence - black arrow), closely approaching the postero-lateral wall of the distal third of the vagina (yellow arrow). The diffusion sequence demonstrates restricted diffusion within the left perineal endometriotic cystic lesion (Blue arrow). The uterine transitional zone appeared thin with no signs of adenomyosis. Uterine ligaments and the ureter showed no abnormalities. Considering these MRI findings, we identified a cystic lesion in the anterior perineum with the following characteristics: • The ureter, labia minora, and anterior vaginal wall were intact. • The possibility of a perineal abscess was ruled out (as it would appear hypointense on T1-weighted images). • Fatty perineal lesion was also ruled out (as it would not show hypersignal on FAT SAT sequences). • There were no signs of adenomyosis ( Fig. 4 ). Fig. 4 The sagittal T2-weighted sequence exhibits no signs of adenomyosis. Fig 4: The ureter, labia minora, and anterior vaginal wall were intact. The possibility of a perineal abscess was ruled out (as it would appear hypointense on T1-weighted images). Fatty perineal lesion was also ruled out (as it would not show hypersignal on FAT SAT sequences). There were no signs of adenomyosis ( Fig. 4 ). Fig. 4 The sagittal T2-weighted sequence exhibits no signs of adenomyosis. Fig 4: The sagittal T2-weighted sequence exhibits no signs of adenomyosis. We considered 2 potential diagnoses for the lesion: an epithelial inclusion cyst and an endometriotic cyst. The location, signal characteristics (mucinous or hemorrhagic), and the patient's history of episiotomy at the same level as the current lesion led us to initially suspect an endometriotic cyst. This diagnosis was confirmed after drainage, which revealed black liquid indicative of a hemorrhagic content. The drainage procedure was performed under local anesthesia, and the patient was advised to return for a clinical follow-up in 3 months, provided there were no complications. The uniqueness of this case lies in the absence of signs of uterine endometriosis, a condition rarely described in the literature. The patient was referred for further gynecological follow-up.

The authors declare that the patient consents for publication of their case.

Perineal endometriosis is a condition that primarily affects women of childbearing age. The diagnosis is typically made using perineal ultrasound and pelvic MRI, while also considering the patient's gynecological history, particularly any prior perineal incisions. Perineal endometriosis requires attention and proper diagnosis in women of reproductive age. Utilizing perineal ultrasound and pelvic MRI, along with a thorough gynecological history, helps in identifying and managing this condition effectively. The provided images assist in understanding the characteristics of perineal endometriosis and its differentiation from other conditions.

Endometriosis is a chronic and benign condition characterized by the growth of endometrial tissue outside the uterus. It affects approximately 10% of women of childbearing age [1] . While the most common locations for extrauterine endometriosis include the ovaries, uterine ligaments, rectovaginal and vesico-uterine spaces, as well as the uterine cervix, perineal endometriosis is an exceptionally rare occurrence. Perineal endometriosis represents the least frequent form of extrauterine endometriosis. Typically, it is associated with signs of adenomyosis in women during their reproductive years. However, our patient's case presents a rare situation where perineal endometriosis occurs without these typical signs. The physiology underlying perineal endometriosis is not well understood and varies depending on whether it is primary or secondary [2] : • Primary perineal endometriosis involves the implantation of endometriotic cells through lymphatic or vascular dissemination or induction. The endometrial cells release substances that prompt undifferentiated mesenchyme to form endometriotic tissue [ 3 , 4 ]. Generally, primary perineal endometriosis is associated with adenomyosis, endometriomas, peritoneal endometriosis, and other locations, as its pathophysiology leads to the implantation of endometrial cells at multiple sites. • Secondary perineal endometriosis occurs when active endometrial cells are implanted on a perineal incision, often an episiotomy. In our patient's case, perineal endometriosis is the unique location resulting from this mechanism. Primary perineal endometriosis involves the implantation of endometriotic cells through lymphatic or vascular dissemination or induction. The endometrial cells release substances that prompt undifferentiated mesenchyme to form endometriotic tissue [ 3 , 4 ]. Generally, primary perineal endometriosis is associated with adenomyosis, endometriomas, peritoneal endometriosis, and other locations, as its pathophysiology leads to the implantation of endometrial cells at multiple sites. Secondary perineal endometriosis occurs when active endometrial cells are implanted on a perineal incision, often an episiotomy. In our patient's case, perineal endometriosis is the unique location resulting from this mechanism. Women with isolated perineal endometriosis often have a history of episiotomies and perineal tears of obstetrical origin, as mentioned earlier [5] . In the presence of a painful and/or tumoral anoperineal syndrome in a woman during genital activity, perineal endometriosis should be considered as a potential diagnosis. It remains a rare condition and warrants attention in clinical evaluations. Perineal endometriosis is clinically characterized by swelling and pain in the perineal region, often exacerbated during menstruation. During the clinical examination, a persistent nodule or occasionally a firm, bluish, and well-contained collection is typically observed in the perineal area. These findings are devoid of inflammatory signs and tend to increase in size during menstruation, with the lesion being sensitive to touch. For exploring perineal endometriosis, ultrasound, and pelvic MRI are considered the gold standard, while CT has limited utility for diagnosis. In some cases, an endoanal ultrasound might be suggested. The radiological appearance of perineal endometriosis varies depending on whether the lesion presents a nodular or cystic aspect: • Nodular form: On ultrasound, the nodular form appears as a strongly hypoechoic, heterogeneous nodule in the anterior perineum, with retractile and irregular contours. MRI reveals an anterior perineal nodular lesion with irregular, star-shaped contours, appearing as hyposignal in both T1 and T2 and shows no enhancement after gadolinium injection. • Cystic form: On ultrasound, the cystic form appears as a well-defined hypoechoic rounded collection with fine echogenic echoes. MRI shows a cystic lesion with hypersignal on T1 and a signal drop in T2 (shading) in some or all parts of the cyst (levels) and no presence of a wall nodule. Nodular form: On ultrasound, the nodular form appears as a strongly hypoechoic, heterogeneous nodule in the anterior perineum, with retractile and irregular contours. MRI reveals an anterior perineal nodular lesion with irregular, star-shaped contours, appearing as hyposignal in both T1 and T2 and shows no enhancement after gadolinium injection. Cystic form: On ultrasound, the cystic form appears as a well-defined hypoechoic rounded collection with fine echogenic echoes. MRI shows a cystic lesion with hypersignal on T1 and a signal drop in T2 (shading) in some or all parts of the cyst (levels) and no presence of a wall nodule. Pelvic MRI also proves valuable in evaluating other extra-perineal locations of endometriosis [5] . The clinical and radiological data allow for differentiation among numerous differential diagnoses of anterior perineal cystic masses. Common differentials include ureteral cystic lesions (such as ureteral diverticulum and Sken's gland cyst) and gynecological cystic masses (such as Muller and Gartner cysts, epithelial inclusion cysts, Bartholin cysts, and endometriotic cysts) [6] . Additionally, although rare, anoperineal melanoma should also be considered due to the bluish coloration of the endometriotic nodule. Various therapeutic approaches can be considered based on the presentation. Asymptomatic forms of endometriosis (which account for 30% of cases) typically require no treatment, and observation is sufficient. However, for fibrous nodular forms, resection is the preferred treatment, while drainage is suitable for cystic forms [7] . The drainage procedure often yields a thick blackish liquid, indicating the presence of hematic content. This article's significance lies in shedding light on an unusual pathology and highlighting the importance of considering perineal endometriosis as a potential diagnosis when encountering a painful perineal mass in young women of childbearing age. It emphasizes the significance of thorough patient interrogation to identify potential predisposing factors, such as a history of episiotomy and obstetric tears.

The most common sites of extra-uterine endometriosis are the ovaries, ligaments supporting the uterus, rectovaginal and vesico-uterine spaces, as well as the uterine cervix. However, perineal localization of endometriosis remains an exceptional occurrence. Perineal endometriosis is often associated with a history of episiotomy, obstetric tear, or perianal surgery, frequently involving curettage. Our patient, a 40-year-old woman with a history of childbirth and episiotomy, experienced left perineal swelling, and the diagnosis of perineal endometriosis was confirmed based on clinical data, pelvic MRI, and post-therapeutic observations.