The gamut of primary retroperitoneal masses: multimodality evaluation with pathologic correlation

Abstract

The retroperitoneum is a large space where primary and metastatic tumors grow silently before clinical signs appear. Neoplastic retroperitoneal diseases may be solid or cystic, primary or secondary and range from benign to aggressive in behavior. Retroperitoneal neoplasms are notable for their widely disparate histologies. The solid primary retroperitoneal neoplasms are extremely uncommon and can be classified based on their tissue of origin into three main categories: mesodermal tumors, neurogenic tumors, and extragonadal germ cell tumors. These tumors can grow to a large size before clinical symptoms occur or become palpable. When symptoms do occur, they are nonspecific. The majority of these masses are malignant and imaging plays a pivotal role in the detection, staging, and pre-operative planning. Benign and malignant masses should be distinguished whenever possible to avoid unnecessary surgical procedures. Macroscopic fat, calcification, necrosis, vascularity, and neural foraminal widening are common imaging features helping for tumor differentiation. Meticulous cross-sectional imaging can triage the patient to the most appropriate therapy. Tumor morphology dictates imaging character, and biologic activity is reflected by positron emission tomography (PET). Complete surgical excision with tumor free margins is essential for long-term survival. Biopsy should be performed in consultation with surgical oncology to avoid complicating curative surgery. This pictorial essay illustrates the spectrum of multidetector computed tomography (MDCT) imaging findings in common and uncommon primary retroperitoneal masses, with an emphasis on cross-sectional imaging features for an adequate tumor characterization and staging.

MR imaging features of benign retroperitoneal paragangliomas and schwannomas

“…Evidence of degeneration, which includes cysts, subacute haemorrhage and microscopic fat, was common for retroperitoneal extra-adrenal paragangliomas and schwannomas, and all tended to be observed [ 28 ]. Takatera et al [ 19 ] reported that 66% retroperitoneal schwannomas showed cystic degeneration, while schwannomas demonstrated an exceptional risk of degeneration [ 11 , 29 ]. In this study, more than 90% of retroperitoneal schwannomas showed the same feature, which was only found in 62.5% of retroperitoneal extra-adrenal paragangliomas, highlighting that fact that this feature is helpful in the differential diagnosis.…”

Practical approach to primary retroperitoneal masses in adults

“…Well-differentiated liposarcoma, which is the most common subtype of liposarcoma, contains mature adipose tissue and is characterized by infiltration of the adjacent structures ( 3 , 4 , 14 , 18 ) . Among the imaging characteristics that favor the diagnosis, making a benign lesion less likely, is lesion size greater than 10 cm, the presence of thick (> 0.2 cm) septa, and foci of nodular enhancement ( 3 , 19 , 20 ) .…”

“…Among the solid lesions that can contain calcifications are neurogenic tumors, dedifferentiated liposarcomas, teratoma, and undifferentiated pleomorphic sarcoma ( 5 , 18 ) .…”

“…Dedifferentiated liposarcoma - Dedifferentiated liposarcoma presents calcifications in approximately 30% of cases; when accompanied by nodules with heterogeneous enhancement (Figure 3), such calcifications are suggestive of areas of tumor dedifferentiation and of a worse prognosis ( 2 , 18 , 31 , 32 ) . In the investigation of liposarcomas, 18 F-FDG PET/CT can facilitate the evaluation of the tumor grade, as well as the staging and postoperative follow-up, through quantification of the FDG uptake of the solid components of the lesion, especially in the dedifferentiated and pleomorphic subtypes ( 18 , 22 , 32 ) . Some authors have suggested that the tumor grade correlates with the rate of glycolysis ( 22 ) .…”

“…Extragastrointestinal stromal tumors manifest as homogeneous or heterogeneous masses, with central necrosis and calcifications. The main differential diagnoses include sarcomas ( 18 ) .…”