Date Published: April 15, 2019
Publisher: Public Library of Science
Author(s): Akira Ogose, Hiroyuki Kawashima, Hiroshi Hatano, Takashi Ariizumi, Taro Sasaki, Tetsuro Yamagishi, Naoki Oike, Syoichi Inagawa, Naoto Endo, Maria Tsokos.
The natural history of asymptomatic retroperitoneal schwannomas is poorly understood. This study aimed at investigating the natural history of incidental retroperitoneal schwannomas. The medical charts and imaging studies of 22 asymptomatic patients under observation for at least 12 months for retroperitoneal schwannomas were reviewed. The duration of follow-up ranged between 13 and 176 months (mean 48 months). In the 22 patients managed by the “wait and see” approach, the average tumor size at initial presentation was 51 mm, which increased to 57 mm at final follow-up. During the final follow-up, 2 patients required surgical treatment for tumor enlargement, while the remaining patients remained asymptomatic without surgery. The average growth rate of the tumors was 1.9 mm/year (range: -1.9 to 8.7 mm/year). The majority of asymptomatic retroperitoneal schwannomas demonstrate minimal growth and may be suitable for management with the “wait and see” approach.
Retroperitoneal schwannomas are rare, comprising between 1 and 3% of all schwannomas . Surgical removal is the mainstay of treatment, offering good prognosis in the event of complete removal [1–6]. However, surgery is an invasive procedure; extensive resections are associated with a higher risk of complications, which may necessitate prolonged hospitalization [1–6]. Retroperitoneal schwannomas are rarely symptomatic  and there are several short-term reports of case series that were managed without surgery [7–10]. Although rare, malignant peripheral nerve sheath tumors also develop in the retroperitoneum. Careful imaging and core needle biopsy are important for differential diagnosis between benign and malignant tumors in the retroperitoneum . The long-term natural history of retroperitoneal benign schwannomas is largely unknown. The present study retrospectively investigated the management of retroperitoneal schwannomas with the “wait and see” policy, and studied the suitability of this approach for asymptomatic cases.
A total of 38 patients were diagnosed with retroperitoneal schwannomas at our institute between 2000 and 2018. Among them, 16 underwent surgical treatment immediately after referral owing to prolonged sciatic pain or numbness in the lower extremity, or because they were suitable candidates for surgery at initial presentation. There were 7 males, and 9 females. The mean patient age was 56 years (range: 37 to 70). All tumors were removed by enucleation via anterior retroperitoneal approach without any complications (S1 Table).
Table 1 shows the characteristics of the follow-up cases. No patient complained of sustained lower extremity pain, or sensory or motor dysfunction at the first visit. The tumor was detected by abdominal ultrasonography examination during routine general investigations in 10 patients, and by MRI in 6 individuals while investigating for temporary low back pain. The remainder were diagnosed by CT, during follow-up imaging for different cancers, investigation for hematuria, and investigation of genital bleeding in 3, 2, and 1 cases, respectively.
Retroperitoneal schwannomas cause abdominal distension, low back pain, lower limb pain and sensory and motor disturbances in the lower extremities [1–6, 11,12]. However, it is not uncommon for asymptomatic tumors to be incidentally discovered, a trend that has become increasingly common for these tumors with advances in imaging. Strauss et al. reported that 13 of the 28 retroperitoneal schwannomas in their cohort were asymptomatic , while Li et al. reported that in 12 out of 82 cases in their series, the tumors were incidentally detected . Among the 38 patients who visited our facility, 16 patients had symptoms that were apparently related to the tumor, necessitating immediate surgery, while 22 were asymptomatic. The high ratio of asymptomatic patients in this cohort may represent the trends of this disease in Japan. Ultrasonography examinations of the abdomen and pelvic cavity are often performed during general investigations in Japan. In this series, the tumor was detected during ultrasonography in 10 of 22 cases. There is no established guideline on the optimal treatment of asymptomatic retroperitoneal schwannomas.