• Lipoma.Benign tumor originating from the fat tissue of the retroperitoneal space. It can be very large with no signs of infiltrations, no solid mass and no vascularization. The main diagnostic sign is the detection of fat-tissue density at CT (about – 100HU) and high intensity signal in MR images or dark images with fat saturation sequences.
• Leiomyoma.This originates from the blood vessels, vas deferens or embryonal remnants.
Usually it shows a rapid growth and necrotic or cystic central degeneration is observed.
Contrast medium reveals a moderate enhancement mainly at the periphery with internal septa.
• Benign teratoma. A specific diagnosis can be made in 70–90% of cases because of typical CT or MR aspects owing to the contemporaneous presence of fat tissue, bone, teeth and fluid. Malignant components can not be ruled out with certainty on the basis of imaging.
• Rare mesenchymal, neurogenic and dysgenetic benign tumors.(Table 2.1). No specific diagnostic features are detectable and the final definition is made by biopsy or surgery.
• Liposarcoma. The most common malignant mesenchymal tumor and more frequent in women. It does not arise from a benign lipoma and the CT density is correlated to the degree of histological differentiation. Lipoma-like liposarcomas with low grade malig- nancy are present, formed mainly of fat and show negative density values at CT or high signals in MR images.
• Leiomyosarcoma.Can arise from retroperitoneal smooth muscle (Fig. 2.5) or vascular wall (cava or aorta). Necrotic or hemorrhagic areas inside the mass can frequently be seen and they show peripheral contrast enhancement. The differential diagnosis from the benign leiomyoma is made on the base of a more aggressive and infiltrating aspect.
The thrombotic obstruction of the inferior vena cava is common in primary leiomyosar- coma and the lesion can manifest itself with edema of the legs, nephritic syndrome or Budd-Chiari syndrome.
Table 2.1 Primary retroperitoneal tumors
Benign Malignant
Mesenchymal (40–80%)
Lipoma Liposarcoma
Leiomyoma Leiomyosarcoma
Fibroma Fibrosarcoma
Rhabdomioma Rhabdomyosarcoma
Hemangioma Hemangiosarcoma
Angiomyolipoma Hemangiopericytoma
Lymphangioma Lymphangiosarcoma
Xantogranuloma Malignant fibrous histiocytoma Neurogenic(10–50%)
Neurinoma
Neurofibroma Neurofibrosarcoma
Benign neuroblastoma Malignant neuroblastoma Benign ganglioneuroma Malignant ganglioneuroma Benign sympathicoblastoma Malignat sympathicoblastoma
Paraganglioma Malignant paraganglioma
Dysgenetic and epithelial (5–19%)
Benign teratoma Malignant teratoma
Chordoma
Urogenital remnant tumors
(a) (b)
Figure 2.5 Leiomyosarcoma of the retroperitoneum originating from the right psoas muscle.
CT in transversal scan (a) and coronal reconstruction (b) after contrast medium administration.
The mass develops in front of the sacrum, displacing the bowel loops and compressing the iliac vessels.
2.5 RETROPERITONEAL LYMPHOMA 27
Figure 2.6 Primary malignant histiocytoma. Large retroperitoneal mass that develops into the abdominal cavity. CT without contrast administration. The mass has a dishomogeneous density with areas of low density and an area of calcification.
• Malignant fibrous histiocytoma.More common in men than in women. The mass does not contain fat or involve the vena cava. It has muscle density values at CT and larger masses show central necrotic areas. Calcifications are observed in 25% of cases (Fig. 2.6).
• Neurofibrosarcoma.Occurs in young patients and the malignant form is not distinguish- able with imaging from the benign form. They may be multiple especially when associated with neurofibromatosis.
• Rare mesenchymal, neurogenic and dysgenetic malignat tumors of the retroperi- toneum.(Table 2.2). These tumors are impossible to differentiate from other masses and require biopsy. Malignancy can be suspected on the basis of the infiltrating nature and the detection of metastasis.
• Very rare primary retroperitoneal tumors.They consist of a heterogeneous group of lesions, rarely observed and with no specific criteria at imaging.
2.5 Retroperitoneal lymphoma
Clinical problem – key concepts
• Lymphomas are frequent in clinical settings and represent about 5% of newly-diagnosed cancers.
• Fever, night sweating, weight loss and superficial nodal enlargement are the most common presenting signs.
• Hodgkin’s and non-Hodgkin’s lymphoma are frequently localized in retroperitoneal lymph nodes.
• Incidence has increased in patients with AIDS or organ transplantation.
• Imaging is the first diagnostic procedure to detect and stage retroperitoneal nodes in patients with systemic lymphatic disease.
Table 2.2 Rare primary retroperitoneal tumors
Tumor Clinic/Pathology Imaging
Hemangiopericytoma 20% originate in the retroperitoneum
Lobulated lesion with calcifications, cystic structure and contrast enhancement at CT and MR Castelman tumor Benign lymphatic tumor with 2
histological subtypes:
vascular-hyaline (90%;
benign) and plasmacellular (symptomatic with fever, anemia, hyper-
gammaglobulin)
Richly vascularized mass with evident enhancement, associated cystic changes, necrosis. May be very large and involve the blood vessel
Neurogenic tumors Common in risk patients (VHL syndrome, neurofibromatosis, tuberous sclerosis) Malignant transformation is observed in 10% of patients
Septated mass with
hypervascularized capsule.
Multiple simultaneous lesions
Cystic lymphangioma Origin from embryonal lymphatic tissue. Rare.
Unilocular or multilocular cystic mass with water density and mild contrast enhancement of the wall.
Septa can be thick and contain calcifications Lymphangiomatosis Very rare tumor, almost
exclusive in women.
Inhomogeneous mass Xanthogranulomatosis Multicentric or systemic tumor
of the histiocytes. The disease is frequently related with retroperitoneal fibrosis.
Generally benign.
Soft tissue dense mass.
Infiltrations of
retroperitoneal structures
Extra-adrenal pheochromocytoma
Develops from the sympathetic chain
No specific signs
Extra-adrenal neuroblastoma
Located in the sympathetic chain outside the adrenals
Large mass with frequent calcifications (80%). Central necrosis
Extra-osseous chondrogenic neoplasms
Atypical retroperitoneal location Large mass, occasionally with calcifications. Cystic or necrotic areas are common
2.5 RETROPERITONEAL LYMPHOMA 29
• Lymphangiography is now rarely performed and the increase in sensitivity and specificity compared with CT is low.
Role of diagnostic imaging
• Detects enlarged retroperitoneal nodes in para-aortic, aortocaval, retrocaval and iliac nodal groups.
• Sonography can not be proposed as a standard of care. Nodes are enlarged and hypoechoic without sound transmission.
• MR imaging is not superior to CT
• The best diagnostic procedure is PET-TC with FDG because the false-positive and false-negative rates are lower since PET allows a functional imaging which is expression of the activity of the disease even in normal sized nodes
• PET has a sensitivity of 90–95% compared with 80–85% of CT. Detects more lesions and is responsible for stage change in 30% of patients
• PET is particularly helpful to differentiate residual active lymphoma from post-therapeutic fibrosis