Leiomyoma is a benign tumor, which is mainly composed of smooth muscle and some fibrous connective tissue elements. Uterine leiomyomas are the most common benign tumors in women. It has been estimated that leiomyomas affect a quarter of women during the reproductive life. However, leiomyomas very rarely arise from the retroperitoneal region, and pathogenesis of retroperitoneal leiomyoma remains obscure. When a retroperitoneal mass is detected in the scan, these tumors are usually believed to be malignant. Also, preoperative diagnosis of a retroperitoneal leiomyoma is rarely possible. We report a case of symptomatic retroperitoneal leiomyomatosis diagnosed by preoperative ultrasonography (USG)–guided biopsy and also the preoperative appearance of the leiomyomas.
A 32-year-old parous woman was referred to our hospital with the suspicion of retroperitoneal malignancy. In her previous history, she had undergone multiple myomectomy 13 years ago. Before she was admitted to our hospital, she was subjected to a second myomectomy because of pelvic pain and multiple leiomyomas. Six months later, she was admitted to another hospital with the complaint of 5-kg weight loss in 1 month. At this center, ultrasonographic examination revealed multiple para-aortic and parailiac solid masses suggesting a malignancy. She was then referred to our hospital with the suspicion of malignancy. Vital signs were within normal limits. Systemic examination did not reveal any abnormalities except bilateral costovertebral and mild abdominal tenderness. Other findings were within normal limits. Gynecological examination showed large and irregular masses on the uterus. Laboratory investigation revealed leukocytosis (17,000/dL) with blood urea nitrogen (BUN) 36 mg/dL and creatinine 1.5 mg/dL. CA125 was 185 IU/mL, and the other tumor markers were within normal limits. Chest and abdominal X-ray did not reveal any pathology. Abdominopelvic USG demonstrated mild hydroureteronephrosis on the left side and multiple solid masses in the left para-aortic and parailiac regions, measuring 4–10 cm in diameter. These were smooth bordered, encapsulated, and thought to be conglomerated lymphadenopathies. There was no evidence of ascites or ovarian pathologies. The abdominal computed tomography confirmed the ultrasonographic findings. A magnetic resonance imaging (MRI) of the abdomen and the pelvis showed two solid masses adjacent to the aorta and left iliac vessels, measuring 8.5 × 6.0 × 4.0 cm and 9.6 × 6.8 × 7.7 cm (Fig. 1). There were no masses in the inferior vena cava or right atrium. USG-guided tru-cut biopsy was performed from the retroperitoneal masses, and pathologic examination of the specimen revealed a benign smooth muscle tumor without mitotic activity or necrosis. She was subjected to exploratory laparotomy due to the pressure effect on the renal collecting system. Four intramural leiomyomas measuring 4–5 cm in diameter were extracted from the uterus. There were no tumors on the peritoneal surfaces. In the retroperitoneal region, at the level of the para-aortic area, there were four separate, firm, smooth bordered masses situated at the left side of aorta, which were easily excised after ligating the main feeding arteries. There was no demonstrable connection to the genital tract. Hemostasis was achieved, and the abdomen was closed in layers. The postoperative course was uneventful. The final pathologic examination revealed that the tumors were composed of smooth muscle cells, and there was no mitotic activity. Histologically, they were leiomyomas. The patient has had no complaint 2 years after retroperitoneal leiomyoma resection. Also, there is no evidence of retroperitoneal leiomyoma recurrence in imaging studies.
Leiomyoma is more frequently found in the fourth and fifth decades of life, and the uterine corpus is the most common site of location. The origin and development of leiomyomas are not well understood, but they probably arise from smooth muscle cells. Also, some evidence suggests that they arise from the smooth muscle of blood vessel walls. Therefore, they can originate wherever smooth muscle cells exist. Although there have been various atypical localizations for leiomyomas, they are exceedingly rare in the retroperitoneum, and we found only a few well-demonstrated case reports in the literature(1–5) (Table. 1).
It is suspected that estrogen plays a role in the development and/or maintenance of uterine leiomyomas. Evidence of hormonal dependence includes the increased frequency of leiomyomas after menarche, the enlargement of leiomyomas during pregnancy, and the regression of leiomyomas after menopause. Furthermore, it has been demonstrated that epidermal growth factor, basic fibroblast growth factor and its receptor, heparin-binding growth factor, transforming growth factor beta, granulocyte–macrophage colony-stimulating factor, and insulin-like growth factors may be involved in the pathophysiology of myomas(6,7). On the other hand, the etiology and pathogenesis of retroperitoneal leiomyomas are unclear. Cases with retroperitoneal leiomyoma after hysterectomy have been reported(2,4). Therefore, it might be speculated that retroperitoneal leiomyomas may be unrelated to uterine leiomyomas. Also, Stutterecker et al. speculated that embryonal remnants of Müllerian or Wolfian tubes might be responsible for the development of retroperitoneal leiomyomas(2).
Common symptoms of retroperitoneal tumors are abdominal discomfort, fatigue, weight loss, and pain radiating to the back. A retroperitoneal mass can be very large and yet be asymptomatic. Rarely, they grow to become clinically apparent. Retroperitoneal tumors are sometimes seen on autopsy or are detected incidentally on routine checkup(1).
Although preoperative imaging and gross appearance are frequently typical for uterine leiomyomas, retroperitoneal leiomyomas are frequently misdiagnosed as malignant tumors. Although Schwartz et al. reported that MRI was highly accurate in the differential diagnosis of uterine leiomyomas from leiomyosarcomas, differential diagnosis on the basis of radiologic finding is difficult(8,9). Therefore, definitive diagnosis of a leiomyoma requires pathologic examination of the specimen. On light microscopic examination, leiomyomas consist of monomorphic spindle cells arranged in interweaving fascicles. These fascicles are separated by variable amounts of hyalinized collagen. Smooth muscle cells are elongated, with abundant eosinophilic cytoplasm and uniform, cigar-shaped nuclei. Usual leiomyomas do not show cytologic atypia or any evidence of necrosis and have a mitotic index of <5/10 in high-power fields. Furthermore, immunohistochemical staining with estrogen, progesterone receptors, desmin, calponin, h-caldesmon, CD10, CD34, c-kit, ki-67, and p53 may be helpful in diagnosing a retroperitoneal leiomyoma and the differential diagnosis of leiomyomas from malignant counterparts(10).
If a retroperitoneal mass is diagnosed as leiomyoma either preoperatively or intraoperatively, the surgeon should excise the tumor as completely as possible, especially in symptomatic patients. However, the tumor can displace important retroperitoneal and vascular structures; therefore, sometimes resection of the tumor might be incomplete. Also, if surgeons are experienced, laparoscopic surgery can be performed in the treatment of retroperitoneal leiomyomas. However, all available cases in the literature were treated with laparotomic approaches. On the other hand, gonadotropin-releasing hormone agonist (GnRH) analogs may be used as an alternative approach after the diagnosis of retroperitoneal leiomyoma was established(11,12)
Differential diagnosis of retroperitoneal pelvic masses includes nonovarian teratomas, neurilemmomas–schwannomas, angiomyxomas, hemangiopericytomas, pheochromocytomas, liposarcomas, leiomyosarcomas, lymphomas, and metastatic tumors(1). Sometimes, they cause pressure effect on the renal collecting system, producing hydroureteronephrosis(3). The tumor may be massive, may displace important retroperitoneal structures, and may be covered with large vessels mimicking malignant growth. Generally, diagnosis of a retroperitoneal tumor is made by imaging studies(1,2). USG is the most useful screening tool for retroperitoneal masses; however, the exact nature of a retroperitoneal tumor cannot be determined by preoperative imaging studies alone. When evaluating a retroperitoneal mass, MRI should be the first choice of investigation because it might be more helpful in distinguishing a malignant tumor from a leiomyoma. Also, it is useful to assess the nature of the tumor and its relationship with adjacent organs and vascular structures. It is difficult to distinguish leiomyosarcoma from leiomyoma on the basis of the radiologic findings alone(9). However, USG-guided sampling of the retroperitoneal tumor may demonstrate the exact nature of the tumor, as in our case, and the therapeutic approach may be changed from surgery to expectant management in asymptomatic and/or medically inoperable patients. On the other hand, determination of the exact nature of the retroperitoneal mass in a small histologic specimen might be difficult. Therefore, the final determination of the true nature of a retroperitoneal mass may need the complete histologic examination of a resected specimen.
In conclusion, when evaluating a retroperitoneal mass, the physician should remember that leiomyomas might arise from this region. MRI is the most reliable imaging technique to evaluate retroperitoneal masses. USG-guided sampling of the mass might be helpful in determining the exact histologic nature of the tumor preoperatively.
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