A recent meta-analysis of retroperitoneal tumors showed that sarcoma comprise a third of retroperitoneal tumors . A variety of neoplasms could occur in the retroperitoneal space, including liposarcoma, lymphoma, epithelial tumors, or metastatic disease from known or unknown primary sites. Benign retroperitoneal tumors include benign neurogenic tumors, paragangliomas, fibromatosis, renal angiomyolipomas, and benign retroperitoneal lipomas. Because of the late presentation of symptoms, tumors have often reached a significant size. Therefore, surgical resections are often incomplete, resulting in local recurrence associated with a less favorable outcome. A preoperative diagnosis is important in order to plan the surgical procedure and adjuvant treatment. However, because of the rarity of the disease, a preoperative diagnosis of UCD was not made in previous case reports of UCD [10, 11], resulting in the surgical exploration of suspicious malignant tumors, including liposarcomas , malignant fibrous histiocytomas , vascular sarcomas , and adrenal neoplasms . Retroperitoneal schwannoma is also rare, but anatomical proximity to adjacent neural structures in imaging studies should raise suspicion . In the present case, the tumor was located in the psoas muscle, and the medial edge of the tumor extended towards the lumbar intervertebral foramen as demonstrated by CT and MRI (Figures 1 and 2) suggesting schwannoma as primary suspicious diagnosis. A characteristic imaging finding of schwannoma is the target sign, which histologically corresponds to peripheral myxomatous tissue and central collagenous tissue . The present case also showed the target-like pattern in T2WI of MRI, surrounded by fat tissue (Figure 2B). The central area of low intensity histologically corresponded to fibrous tissue (Figure 5), which could be found in abdominal CD. However, Zhou et al. reported that a central area of low-density on CT and low-intensity on MRI showed a fissured and radial pattern , which was found in our case. Therefore, the presence of the target sign on MRI as well as the shape of the central low-intensity area may help to distinguish CD from schwannoma.
Because the findings by CT and MRI did not lead to a definite preoperative diagnosis, radionuclide studies, including PET, were performed. Negativity of gallium scintigraphy suggested malignant lymphoma as a less suspected diagnosis. It is reasonable that CD could be positive for gallium scintigraphy because of its nature of lymphatic proliferative disease . However, its positivity would depend on the inflammatory activity of an individual case, which explains why the present case was negative for gallium-67. PET recently became a common modality for the diagnosis and evaluation of therapeutic effects on malignant tumors. A recent study revealed that the median SUV of seven patients with active MCD was 4.8 (range, 2.6-9.3) , which was comparative to that of the present case (SUV, 4.7). High cellularity and inflammatory nature of CD may lead to high SUV, making it difficult to exclude malignant tumor before biopsy. Oida et al. reported a case of UCD that showed an SUV of 4.5 in the PET study, resulting in its incorrect preoperative diagnosis as lymphoma . Therefore, even with the most advanced imaging techniques, including PET, the preoperative diagnosis of retroperitoneal tumors, including CD, still seems difficult .
HV-UCD is the most common variant of CD and accounts for 72% of all CD variants . Plasma cell type CD (PC-UCD) displays of mature plasma cell proliferation in the areas surrounding the germinal centers, without accompanyinghyalinized vessel formation [3, 8]. PC-UCD and PC-MCD account for 18% and 10% of all PC variants, respectively. The treatment differs by the type of CD, reflecting the clinical behavior of each variant. Both HV-UCD and PC-UCD can be cured by complete resection of the affected lymph node; recurrence, metastasis, or mortality have not been reported [2, 3, 21]. Rare cases of PC-UCD show remnant systemic symptoms after resection; however, additional therapy for those PC-UCD cases is not well established . Radiation therapy may be a treatment option for cases of surgically unresectable UCD [2, 21]. Cure can be achieved by radiotherapy in selected patients with UCD, although its role in UCD treatment remains unclear . Regarding the follow-up for UCD, patients without systemic involvement should have an additional radiological assessment 6–12 months postoperatively to verify the cure; additional testing or therapy should be considered at the onset of new symptoms .
Surgeons should be prepared for massive bleeding during the resection of CD, especially in the deep portion of the body close to major vessels. Preoperative angiography clearly visualized the feeding vessels that aided intraoperative detection and ligation of the feeding lumbar artery. If such an imaging study is not performed and the preoperative diagnosis does not include such hemorrhagic tumors, massive bleeding may obstruct surgical procedures and patients may be at risk of fatal blood loss. Although we chose the retroperitoneal approach in the decubitus position in the present case, the transperitoneal approach may have been an alternative option for tumor resection. One of the reasons for us choosing this is approach is familiarity with the retroperitoneal approach for spinal surgery. Another reason is that exploration of the intervertebral foramen may have been required because schwannoma was the most suspected preoperative diagnosis. If UCD is preoperatively suspected and the surgeons are familiar with the transperitoneal approach, the wide operative field obtained with that approach may be helpful to reduce intraoperative bleeding.