Spontaneous Parasitic Pedunculated Myoma Presenting the Absence of Uterine Smooth Muscle Cells in the Stalk - A Case Report.

A 51-year-old patient (gravida 1, para 0) with no history of abdominal surgery was referred to our hospital from a private clinic because of dysmenorrhea with multiple myomas. The symptoms did not improve despite using dienogest for dysmenorrhea. We recommended radical surgery because treating dysmenorrhea with medical therapy was challenging, and the patient agreed. Magnetic resonance imaging revealed a 6 cm-sized fibroid on the anterior wall of the uterine body and a 4 cm-sized fibroid on the posterior wall. Multiple small myomas were observed under the serosa and within the muscle layers. A 3 cm-sized left ovarian tumor was identified, which was a mature cystic teratoma. Hence, robotic-assisted laparoscopic hysterectomy, left salpingo-oophorectomy, and right salpingectomy were recommended. Robotic-assisted surgery was performed using the da Vinci ® Xi system (Intuitive Surgical, Inc., Sunnyvale, CA). First, an 8-mm camera port was inserted 4 cm above the umbilicus. After placing the patient in the Trendelenburg leg position (15° head-down), an 8-mm port for the assistant was placed in the left lower abdomen. The remaining three 8-mm ports were placed 8 cm, 7 cm, and 14 cm to the left, right, and right of the camera port, respectively. After robot docking, a Force Bipolar, a camera (30° oblique-viewing laparoscope), an EndoWrist Monopolar Spatula, and a Vessel Sealer were attached to the first, second, third, and fourth arms, respectively. Intraoperative findings revealed a pedunculated subserosal myoma measuring approximately 3 cm that was firmly attached to the right-side retroperitoneum of the vesicouterine pouch [ Figure 1 a and b]. It initially appeared as a parasitic myoma. However, the myoma had a thick stalk that was not twisted [ Figure 1 c]. The patient had no medical history of myomectomy. Spontaneous parasitic myoma on the right-side retroperitoneum of the vesicouterine pouch at the robotic-assisted laparoscopic hysterectomy. (a-c) A pedunculated subserosal myoma adhered to the retroperitoneum with the stalk (white arrow) connected to the uterine corpus, (d) The stalk (white arrow) was divided using da Vinci ® Xi Vessel Sealer, (e and f) Leiomyoma with retroperitoneal adipose tissue was resected (white arrow) using da Vinci ® Xi EndoWrist Monopolar Spatula The stalk was sealed and separated using the Vessel Sealer [ Figure 1 d]. The myoma with retroperitoneal adipose tissue was removed using an EndoWrist Monopolar Spatula [ Figure 1 e and f]. Surgical operation was performed without any complications [ Figure 2 a]. The operative time was 2 h and 27 min, and blood loss was minimal. Gross and histological images of extracted organs, including parasitic myoma. (a) Gross image of the uterus with multiple myomas, the left adnexa, and the right fallopian tube, (b) Gross image of parasitic myoma, (c) Histological image of parasitic myoma and stalk roots (white arrowhead) with thermal denaturation. There are no obvious uterine smooth muscle cells in the basal stalk adjacent to the myoma (yellow arrowhead), which has not undergone heat denaturation (H and E, ×12.5), (d) Bundled growth image of spindle tumor cells showing differentiation into uterine smooth muscle (H and E, ×40), (e) Expanded image of the stalk of parasitic myoma revealed the absence of uterine smooth muscle cells and the presence of only muscular arteries (white arrowhead) and fibrous connective tissues with thermal denaturation (H and E, ×40), (f) Endometriosis (white arrowhead) between parasitic myoma and the adipose tissue of the retroperitoneum (H and E, ×40) Gross imaging of the tumor attached to the peritoneum revealed a leiomyoma [ Figure 2 b]. Pathological findings presented spindle tumor cells that had differentiated into uterine smooth muscle cells arranged in intersecting fascicles [ Figure 2 c and d]. The stalk of the leiomyoma had lost the uterine smooth muscle cells and contained only muscular arteries and fibrous connective tissue [ Figure 2 c and e]. Endometriosis was observed between the leiomyoma and adipose tissues of the peritoneum [ Figure 2 f]. The left ovarian tumor was a mature cystic teratoma, and there were no findings in the right fallopian tube. The absence of uterine smooth muscle cell continuity between the uterine body and fibroid attached to the retroperitoneum indicated that this fibroid was a spontaneous parasitic myoma.

Parasitic myomas are rare extrauterine variants of fibroids.[ 1 ] Two causes of parasitic myomas are: iatrogenic[ 2 3 4 ] and spontaneous.[ 5 6 7 8 ] Missing fragments of fibroids can lead to parasitic myomas, which receive an alternative blood supply from other organs.[ 9 ] Parasitic myomas may be revealed incidentally, or they may cause symptoms of abdominal pain, such as round ligament fibroid.[ 10 11 ] “Spontaneous” parasitic myoma was believed to be caused by twisting of a pedunculated subserosal leiomyoma, detachment, and development by neovascularization from other organs.[ 1 ] However, evidence to support this hypothesis is unavailable. Herein, we report a case of spontaneous parasitic pedunculated subserosal myoma with pathological findings presenting with the absence of uterine smooth muscle cells in the stalk observed during robotic-assisted laparoscopic hysterectomy.

To our knowledge, this is the first report of a spontaneous parasitic pedunculated subserosal myoma with pathological findings presenting the absence of uterine smooth muscle cells in the stalk. In addition to the torsion of the stalk of pedunculated subserosal fibroids, spontaneous parasitic myoma may result from stalk degeneration through an unknown mechanism. Therefore, more cases are required to test this hypothesis. This study was conducted in accordance with the ethical principles outlined in the Declaration of Helsinki and its amendments. The authors certify that they have obtained all appropriate patient consent form. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that her name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed. Naoki Shibata, Michihisa Shiro, Noriyoshi Oki, Takahiro Watanabe, Hitomi Futaki drafted, edited the manuscript. Shigeki Yoshida reviewed and edited the manuscript. All authors approved the final submitted manuscript. Data sharing not applicable to this article as no datasets were generated or analyzed during the current study. Nil. There are no conflicts of interest.

This case report presents two novel clinical features. First, a spontaneous parasitic pedunculated subserosal myoma with pathological findings presenting with the absence of uterine smooth muscle cells in the stalk was found. Second, this report reveals that parasitic myomas in the retroperitoneum could be safely resected using robotic surgery. Pedunculated subserosal myomas usually receive blood flow from the uterine corpus through the stalk. Some pedunculated subserosal myomas rarely receive collateral parasitic blood flow from other organs, including the omentum, bladder, and peritoneum.[ 12 ] In past reports, spontaneous parasitic myomas received their blood supply mainly from the omental arteries and veins, with a thin cord-like stalk connected to the uterine corpus.[ 7 8 ] However, a pathological examination of the thin cord-like stalks was not performed in these reports. In our case, pathological findings of the stalk of the parasitic myoma revealed the absence of uterine smooth muscle cells [ Figure 2 c and e]. One of the mechanisms underlying the formation of the thin cord-like stalk of parasitic myomas may be the torsion of pedunculated subserosal myomas, leading to ischemic change and transection. However, in our case, although the stalk did not appear to be twisting during robotic surgery [ Figure 1 a-c], it lost uterine smooth muscle cells and had only muscular arteries and fibrous connective tissues. Upon reviewing the surgical video after pathological diagnosis, we observed that parasitic myoma stalks had a lower tissue density than typical subserosal myomas [ Figure 1 c]. Unlike open surgery, this finding was observed because robotic surgery allows for proximity to the tissue and clear images. Pathological findings also revealed endometriosis between the leiomyoma and adipose tissues of the peritoneum [ Figure 2 f]. We assumed that after a pedunculated subserosal myoma adhered to the retroperitoneum owing to endometriosis, the fibroid mainly received blood flow from the retroperitoneum, and the stalk gradually degenerated. We hypothesized that one of the mechanisms underlying the occurrence of spontaneous parasitic myomas was as follows: (1) Adhesions occurred between the pedunculated subserosal leiomyoma and the retroperitoneum or omentum due to endometriosis. (2) After the myoma received collateral parasitic blood flow from the retroperitoneum or omentum, the stalk degenerated, and uterine smooth muscle cells were lost through an unknown mechanism. (3) The subserosal myoma was detached from the uterine body due to progressive degeneration of the stalk. Eventually, spontaneous parasitic myoma was completed. Subsequently, the parasitic myoma in the retroperitoneum was safely resected using robotic surgery. Only two cases of parasitic myoma resection using robotic surgery have been reported.[ 13 14 ] Parasitic myomas can occur at various locations within the abdominal cavity. With conventional laparoscopy, surgery may be difficult depending on the location within the abdominal cavity. However, owing to the advantages of robotic surgery, it can be performed in these complex locations.