Endometriosis in an ectopic kidney: a rare case report and literature review

Endometriosis, the presence of endometrial glands and stroma outside the uterine cavity, is the second most common pelvic disorder and the most common cause of pelvic pain in women of reproductive age [1]. Most lesions usually located within the reproductive system, but rarely occurs outside the pelvis, especially in the kidney [2].

Endometriosis in the ectopic kidney is very rare and has not been reported in the literature yet, to the best of our knowledge. Herein, we report our experiences with regard to the clinical and imaging manifestations of endometriosis in an ectopic kidney to raise awareness of this rare disease.

A 19-year-old girl was admitted to our hospital for an ectopic left kidney during physical examination. She noted occasional mild peri-abdominal pain. Otherwise, she was healthy and physical examinations were unremarkable.

Endometriosis is the second most common pelvic disorder and the most common cause of pelvic pain in women of reproductive age [1]. The main site of the disease is ovary, and the urinary tract involvement is rare, mainly the bladder (80%), followed by ureters (15%) and kidneys (<5%) [21]. To date, only 17 cases of renal endometriosis have been reported, the first case was reported by Marshall in 1943 [3]. To our knowledge, this case is the first report of endometriosis within ectopic kidney.

Several theories of the pathogenesis of endometriosis have been proposed, including embryonic, migratory, and immunologic theories [4‐7]. Concretely, embryonic theories indicate that endometriosis results from metaplastic changes of Wolffian, Mullerian, and occasionally peritoneal (celomic) structures. Migratory theories suggest that retrograde menstruation, lymphovascular metastasis, and direct extension allow for transplantation of the endothelial cells into ectopic sites. Immunologic theories suggest that a suboptimal immune response maybe result in ectopic endometrial implantation [6‐36]. Simone Laganà et al. summarized recent evidences about the pathogenesis of endometriosis in remote sites and believed the retrograde menstruation of stem/progenitor cells from endometrial niches to the peritoneal cavity and the migration of bone marrow-derived stem cells through peripheral circulation may underlie the development of endometriosis in remote sites (e.g., kidney, nose and so on) [6‐10]. In addition, accumulating evidence demonstrates that immune cells, adhesion molecules, extracellular matrix metalloproteinase and pro-inflammatory cytokines activate/alter peritoneal microenvironment, creating the conditions for differentiation, adhesion, proliferation and survival of ectopic endometrial cells [6‐9]. For example, a recent study found that the quantity of M1 and M2 macrophages in ovarian endometriomas at different stages of the disease were different and implied that the activity and polarization of macrophages maybe play a key role in development of endometriosis [10]. Some researches proposed new insights on the pathogenesis and pathophysiology of endometriosis from novel perspectives. Such as, Murgia et al. applied a metabolomic strategy to explore metabolic alteration in patients with endometriosis to better understand the pathophysiology of endometriosis [11]. Viganó et al. indicated that small bowel permeability may be associated with the maintenance of low-grade inflammation of endometriosis [12].

Endometriosis is regarded as an estrogen-dependent process, with clinical symptoms of dysmenorrhea, dyspareunia, and profuse bleeding [4]. Nevertheless, the clinical presentation of renal endometriosis is diverse and atypical. The absence of typical clinical manifestations may be due to the fact that the renal endometriosis is confined to the renal cortex without involvement the renal calyces. According to previous reports, most of the clinical manifestations of renal endometriosis are abdominal pain and gross hematuria. Long-term periodic bleeding may lead to the gradual increase of hemorrhagic cysts in the kidney tissue and even invasion into the renal calyces, which can result in ureteral obstructions, and that is the main cause of abdominal pain and hematuria [13]. Although peritoneal superficial lesions and ovarian endometriomas represent the majority of endometriotic implants within the pelvis, deep infiltrating endometriosis and extra-pelvic endometriosis are the most challenging conditions to face off. On the one hand, severe symptoms of posterior deep infiltrating endometriosis, such as dyschezia, dysuria, dyspareunia and voiding alterations due to neurotrophism and neurotropism, seriously lower quality of life [14]. On the other hand, the definite diagnosis of extra-pelvic endometriosis is difficult and hysteretic and thus maybe delay timely treatment for patients with endometriosis. In addition, some endometriosis lesions may be very small or hidden. Vizzielli et al. tried to use intraoperative near-infrared radiation imaging after intravenous injection of indocyanine green during robotic operations for removing endometriosis lesions to improve detection rates and acquired some beneficial findings [15]. Despite sometimes medical therapy is enough to reduce symptoms and signs [16], in a large number of patients a complete eradication, with nerve-sparing and vascular sparing approach is needed to restore the normal pelvic anatomy and its functions [17].

In view of renal endometriosis is so rare, there are currently no treatment guidelines [23]. Clinical treatment mainly includes symptom relief and radical treatment. Therefore, the treatment of renal endometriosis should be carried out according to the patient’s clinical symptoms, the characteristics of the lesion, and the patient’s reproductive plan [33]. If an asymptomatic patient has no change in the lesions on follow-up review, no definitive renal therapy is usually required [8]. In addition, for patients of reproductive age, hormone therapy, such as oral contraceptives can relieve abdominal pain and is the best treatment option in the short-term [20]. Although renal endometriosis is a benign condition, surgery is usually considered, laparoscopic management in particular, as the feasibility of this treatment has been widely proven to reduce the length of hospital stay [35, 36]. Surgical intervention is required if there is a potential risk of ureteral obstruction and even loss of renal function due to repeated bleeding from endometriosis of the kidneys [37].

In a word, this article reports the clinical features of renal endometriosis of the first case of endometriosis in an ectopic kidney. Although imaging features are helpful in renal endometriosis, the final diagnosis relies on pathological findings.