Practical approach to primary retroperitoneal masses in adults

Abstract

Primary retroperitoneal masses constitute a heterogeneous group of uncommon lesions and represent a challenge due to overlapping imaging findings. Most are malignant lesions. Although they are more prevalent in adults, they can occur at any age. Such lesions are classified as primary when they do not originate from a specific retroperitoneal organ and are divided, according to the image findings, into two major groups: solid and cystic. The clinical findings are nonspecific and vary depending on the location of the lesion in relation to adjacent structures, as well as on its behavior. The main imaging methods used for staging and surgical planning, as well as for selecting the biopsy site and guiding the biopsy procedure, are computed tomography and magnetic resonance imaging. In most cases, the treatment is challenging, because of the size of the lesions, vascular involvement, or involvement of adjacent organs. In this article, we present a review of the retroperitoneal anatomy and a practical approach to the main imaging features to be evaluated, with a view to the differential diagnosis, which can guide the clinical management.

Keywords: Magnetic resonance imaging; Retroperitoneal neoplasms/diagnosis; Retroperitoneal space/anatomy & histology; Tomography, X-ray computed.

Figure 1

Retroperitoneal anatomy. The anterior pararenal space is delimited anteriorly by the posterior parietal peritoneum, posteriorly by the anterior renal fascia, and laterally by the lateroconal fascia. It includes the pancreas (P) and second portion of the duodenum (D), as well as the ascending and descending colon (C). The posterior pararenal space is delimited anteriorly by the posterior renal fascia and posteriorly by the transversal fascia. It contains fat. The perirenal space, which contains the kidneys and adrenal glands, is located between the anterior and posterior renal fasciae. The central region includes the aorta and inferior vena cava, as well as lymphatic chains and nerve structures. APS, anterior pararenal space; PRS, perirenal space; PPS, posterior pararenal space; PPP, posterior parietal peritoneum; ARF, anterior renal fascia; PRF, posterior renal fascia; LCF, lateroconal fascia; TF, transverse fascia.

Figure 2

Mature teratoma in a 23-year-old female. CT scan showing a retroperitoneal mass with fat components, cystic areas, and calcifications (arrow). These findings, especially the fat component, are suggestive of a germ-cell origin. Note the anterior displacement of the aorta in relation to the vertebral body-an indirect sign of retroperitoneal location (arrowhead). The diagnosis was confirmed by percutaneous biopsy.

Figure 3

Dedifferentiated liposarcoma. A: 58-year-old male. CT scan showing an infiltrative lesion with solid and fat components (arrow).Note the displacement of the right kidney (arrowhead), inferring location in the posterior pararenal space, and the focus of calcification (circle) suggesting dedifferentiation of the tumor. B,C: 44-year-old female. Contrast-enhanced T1-weighted MRI sequence with fat saturation (B) showing a fat-containing infiltrative lesion (signal loss) and nodules infiltrating the abdominal wall (arrow). An ultrasound-guided percutaneous biopsy was performed, and an ¹⁸F-FDG PET/CT scan showed hypermetabolism (arrow in C), corresponding to the foci of dedifferentiation.

Figure 4

Retroperitoneal paraganglioma in a 24-year-old male. CT and ¹⁸F-FDG PET/CT scans (A and B, respectively) showing hypervascular nodular lesions with hyperglycolysis adjacent to the aortoiliac bifurcation.

Figure 5

Ganglioneuroma in a 31-year-old female. CT scan showing a retroperitoneal lesion with a pseudocystic aspect (arrow).

Figure 6

Retroperitoneal leiomyosarcoma in a 56-year-old female. CT scan showing a bulky retroperitoneal lesion with heterogeneous enhancement and foci of necrosis. Note the extensive contact with the inferior vena cava (arrow).

Figure 7

Retroperitoneal cystic lymphangioma in a 37-year-old male. CT scan showing a retroperitoneal cystic lesion (arrow), displacing the bowel loops anteriorly and in contact with the pancreas. Surgical resection was performed, and the pathology showed proliferation of dilated lymphatic vessels, without atypia, consistent with lymphangioma.

Figure 8

Mantle zone growth pattern. Erdheim-Chester disease in a 62-year-old male. CT scans (A,B) showing perirenal solid tissue (mantle zone growth pattern) surrounding the renal hilum (arrow in B). No bilateral hydronephrosis was observed.

Figure 9

Algorithm demonstrating the practical evaluation of retroperitoneal masses based on the main image characteristics (fat, cystic aspect, myxoid stroma, necrosis, and a mantle zone growth pattern).

Figure 10

Clinical management of the main retroperitoneal masses.