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Retroperitoneal masses are lesions that arise within the retroperitoneal space, which extends from the diaphragm to the pelvic brim, posterior to the parietal peritoneum and anterior to the transversalis fascia.

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Anatomical compartments

For localization, the retroperitoneum is divided into:

  1. Anterior pararenal space (between posterior peritoneum & anterior renal fascia): pancreas, duodenum, ascending/descending colon.
  2. Perirenal space (between anterior & posterior renal fascia): kidneys, adrenal glands, proximal ureters, renal vessels.
  3. Posterior pararenal space (between posterior renal fascia & transversalis fascia): fat, no major solid organs.
  4. Great vessel/central compartment: aorta, IVC, lymphatics, autonomic nerves.

![Illustration of the retroperitoneum at the level of the kidneys demonstrating the retroperitoneal compartments (PP: Parietal peritoneum, APF: Anterior pararenal fascia, LCF: Lateroconal fascia, APS: Anterior pararenal space, PRS: Perirenal space, PPS: Posterior pararenal space, RRS: Retrorenal space, PPS, TF: Transversalis fascia).

Montanarella M, Ignacio C, Jeronimo M, et al. Retroperitoneal anatomy with the aid of pathologic fluid: An imaging pictorial review. Journal of Clinical Imaging Science. 2023;13:36-36. doi:https://doi.org/10.25259/jcis_79_2023](attachment:7affec5c-4827-4cd4-8dc0-cec0c51b8634:JCIS-13-36-g001.png)

Illustration of the retroperitoneum at the level of the kidneys demonstrating the retroperitoneal compartments (PP: Parietal peritoneum, APF: Anterior pararenal fascia, LCF: Lateroconal fascia, APS: Anterior pararenal space, PRS: Perirenal space, PPS: Posterior pararenal space, RRS: Retrorenal space, PPS, TF: Transversalis fascia).

Montanarella M, Ignacio C, Jeronimo M, et al. Retroperitoneal anatomy with the aid of pathologic fluid: An imaging pictorial review. Journal of Clinical Imaging Science. 2023;13:36-36. doi:https://doi.org/10.25259/jcis_79_2023

![Illustration of the retroperitoneal space at and below the level of kidneys.

Montanarella M, Ignacio C, Jeronimo M, et al. Retroperitoneal anatomy with the aid of pathologic fluid: An imaging pictorial review. Journal of Clinical Imaging Science. 2023;13:36-36. doi:https://doi.org/10.25259/jcis_79_2023](attachment:d74ec90f-5a6e-4d4c-8c79-b4de49e67271:JCIS-13-36-g002.png)

Illustration of the retroperitoneal space at and below the level of kidneys.

Montanarella M, Ignacio C, Jeronimo M, et al. Retroperitoneal anatomy with the aid of pathologic fluid: An imaging pictorial review. Journal of Clinical Imaging Science. 2023;13:36-36. doi:https://doi.org/10.25259/jcis_79_2023

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![Illustration of the pelvic retroperitoneal spaces on sagittal and axial views.

Montanarella M, Ignacio C, Jeronimo M, et al. Retroperitoneal anatomy with the aid of pathologic fluid: An imaging pictorial review. Journal of Clinical Imaging Science. 2023;13:36-36. doi:https://doi.org/10.25259/jcis_79_2023](attachment:6bf3e9cf-c5e8-40de-ad69-c1d8886035d2:JCIS-13-36-g013.png)

Illustration of the pelvic retroperitoneal spaces on sagittal and axial views.

Montanarella M, Ignacio C, Jeronimo M, et al. Retroperitoneal anatomy with the aid of pathologic fluid: An imaging pictorial review. Journal of Clinical Imaging Science. 2023;13:36-36. doi:https://doi.org/10.25259/jcis_79_2023

Etiopathology / Classification

Primary Retroperitoneal Tumors (rare, ~0.2% of all tumors)

Tissue origin Pathology
Mesenchymal
(most common) • Liposarcoma (most common primary retroperitoneal sarcoma)
• Leiomyosarcoma (from smooth muscle of vessels)
• Malignant fibrous histiocytoma / undifferentiated pleomorphic sarcoma
• Fibrosarcoma, rhabdomyosarcoma
• Extraskeletal osteosarcoma / chondrosarcoma
Neurogenic • Benign nerve sheath tumors: Schwannoma, neurofibroma
• Malignant peripheral nerve sheath tumor (MPNST)
• Paraganglioma.
Germ cell tumor Teratoma, seminoma (often in younger patients).
Vascular Hemangioma, angiosarcoma, aneurysms mimicking mass.
Others Lymphangioma, mesothelioma.

Secondary / Extension tumors

Non-neoplastic causes