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
• Enlarged nodes can form a conglomerate masses or a large homogeneous mass in which individual nodes are no longer recognized.
• The nodal masses show a soft tissue density as the other solid viscera and sometimes areas of reduced density due to tissue degeneration.
2.6 Cystic retroperitoneal masses
Clinical problem – key concepts
• Retroperitoneal cystic masses are uncommon. They can be classified as either neoplastic or non-neoplastic.
• Neoplastic lesions include cystic lymphangioma, mucinous cystadenoma, cystic teratoma, m¨ullerian cyst, epidermoid cyst, and cystic change in solid neoplasms. Non-neoplastic lesions include pancreatic pseudocyst, non-pancreatic pseudocyst, lymphocele, urinoma, and hematoma.
• The most important clinical parameters include patient gender, age, symptoms, and clinical history.
Role of diagnostic imaging
• The widespread use of axial imaging modalities has increased the detection rate of retroperitoneal cystic lesions.
• Some features may suggest a specific diagnosis. Imaging may provide important infor- mation regarding lesion location, size, and shape; the presence and thickness of a wall;
the presence of septa, calcifications, or fat; and involvement of adjacent structures.
• Conventional radiology does not offer any utility in detection and characterization of cystic masses.
• Sonography can detect easily urinomas and hemorrhage as fluid collections but it is not always able to differentiate between them.
• CT and MR are the preferred diagnostic modalities to investigate retroperitoneal cystic masses.
General imaging criteria
• low-attenuation mass sometimes containing tiny calcifications
• localization characteristics for some pathologies (e.g. presacral, or in the obturator space)
• absence of infiltration
• no lymph nodes enlargement
• small variations in density values at CT after contrast administration
• solid signal intensity at MR T2-weighted sequences
2.6 CYSTIC RETROPERITONEAL MASSES 31
Specific imaging criteria
• Cystic lymphangioma. Uncommon, congenital benign tumors and occur due to failure of the developing lymphatic tissue. Cystic lymphangiomas can develop anywhere in the perirenal, pararenal, or pelvic extraperitoneal spaces. They may cross more than one compartment of the retroperitoneum.
• Mucinous cystadenoma. Rare retroperitoneal cystic lesions that occur in women with normal ovaries. Early diagnosis of primary mucinous cystadenoma is important because of its malignant potential. They usually appear as a homogeneous, unilocular cystic mass at CT. Differentiating this mass from cystic mesothelioma, cystic lymphangioma, and non-pancreatic pseudocyst is difficult.
• Cystic teratoma. Retroperitoneal cystic teratomas are composed of well-differentiated derivations from at least two of the three germ layers (ectoderm, mesoderm, endoderm).
A cystic teratoma is likely to be benign, whereas a solid teratoma is likely to be malignant.
At CT, a mature teratoma of the retroperitoneum consist of a complex mass containing a well-circumscribed fluid component, adipose tissue, and calcification (Fig. 2.8).
• M ¨ullerian cyst.M¨ullerian cyst of the retroperitoneum is an extremely rare disease that is thought to be a subtype of urogenital cyst. At CT, m¨ullerian cyst appear as a unilocular or multilocular thin-walled cyst containing clear fluid.
• Epidermoid cyst.Epidermoid cysts are rare congenital lesions of ectodermal origin and can occur anywhere from the head to the foot. At CT, epidermoid cysts generally appear as thin-walled, unilocular cystic masses with fluid attenuation.
• Cystic change in solid neoplasm.Occasionally, paraganglioma and neurogenic tumor can be cystic. They can be associated to clinical symptoms because of the catecholamines they produce. At CT, retroperitoneal paragangliomas usually have homogeneous soft-tissue attenuation or central areas of low attenuation.
Figure 2.8 Retroperitoneal cystic teratoma. CT scan after contrast medium administration.
A large well defined mass with fluid content and solid internal areas, involving the right retroperitoneal space and displacing the adjacent structures. A regular enhanced capsula and a small calcification is present.
• Lymphocele. Lymphoceles are fluid-filled cysts without an epithelial lining that occur after pelvic or retroperitoneal lymphadenectomy or renal transplant surgery. They occur in 12–24% of patients who undergo radical lymphadenectomy. At CT, a lymphocele appear as a low-attenuation mass. Negative attenuation values due to fat within the fluid are rare but are highly suggestive of a lymphocele.
2.7 Retroperitoneal metastases
Clinical problem – key concepts
• Retroperitoneal and pelvic lymph nodes can be the site of spread of malignant cell sec- ondary to testicular tumors, melanoma, prostate cancer, bladder TCC, ovarian carcinoma, or lung and breast tumors.
• Enlarged lymph nodes can be observed in patients without malignancies and accounts for 6% of nodes disease. Sarcoidosis, tuberculosis, rheumatoid arthritis, amyloidosis, Whipple and Crohn’s disease, cirrhosis and chronic hepatitis have to be considered in the differential diagnosis.
• Lymph node enlargement is frequent in AIDS patients as part of systemic lymphatic dis- ease. A non-Hodgkin’s lymphoma is the most frequent type of AIDS-related lymphoma.
Kaposi’s sarcoma can manifest as bulky retroperitoneal adenopathy and tumor infiltrating the retroperitoneum. Opportunistic infections are common in AIDS patients, most often caused by tuberculosis or fungal infection.
Imaging criteria
• In testicular tumors the lymphatic drainage follows the gonadal vessels and the metastases are generally located at the level of the renal hilum and in the adjacent para-aortic and paracaval space. Rapidly growing discrete or confluent low density nodes are characteristic of seminomas. MR imaging can be used because the young age of patients with testicular tumors. Retroperitoneal nodes show a low or intermediate signal intensity in T1-weighted images and high intensity signal in T2. Nodes may enhance after contrast administration like the primary tumor.
• Tumors that origin from pelvic organs as prostate, bladder, uterus and ovary usually show initial met to the obturator and iliac nodes and to the retroperitoneal nodes in advanced stage (Fig. 2.9). They are usually smaller in size compared to node enlargement observed in lymphomas or testicular cancer.
• Melanoma node metastases generally have high intensity signal in T1-weighted images.
• The CT or MR diagnosis of pathological lymph nodes is based on the enlargement of normally oval-shaped and smooth nodes. The upper limit of normality varies according to the site: 6–7 mm for retrocrural, 12–15 for para-aortic and paracaval, and 18–20 mm for iliac and obturatory nodes.
• Enlargement is not pathognomonic for malignancy because inflammatory or reactive changes are a very common cause of increased size.
2.8 RETROPERITONEAL FIBROSIS (ORMOND’S DISEASE) 33
Figure 2.9 Retroperitoneal metastases secondary to colonic carcinoma. CT of the abdomen in transversal scan at the level of the kidney, with contrast medium. Multiple confluent nodules of different size displacing the main vessels and the bowel. Some nodules show extensive necrotic areas, while others are still homogeneous.
• The detection of multiple nodes of 10 mm or the presence of a bulky mass is indicative of malignancy.
• The loss of the normally present peri-aortic and pericaval fat layer is considered a sign of infiltration.
• Central hypodense areas in enlarged nodes is generally indicative of necrosis, fat deposi- tion and is nor specific for malignancy.
• Hydronephrosis due to ureteral compression or infiltration is often observed in retroperi- toneal metastastasis and is indicative of malignancy.
• Bone destruction or muscular infiltration with nerve infiltration is very common in sec- ondary lymph node involvement.
2.8 Retroperitoneal fibrosis (Ormond’s disease)
Clinical problem – key concepts
• Chronic inflammatory fibrosing disease localized in the connective tissue of the lumbar retroperitoneum which may compromise ureters and blood vessels.
• Primary idiopathic form is observed in 70% of patients, while the other 30% is secondary to drug abuse, aortic aneurysm, tumors and other rare causes.
• The clinical symptoms are non-specific and the most commonly observed are abdominal pain extended from the back to the genital area (80–90%), weight loss (40–50%), gas- trointestinal discomfort (25–50%), anorexia (13%), anuria (10–16%), progressive renal failure (40%).
• The majority of patients come to observation because of renal insufficiency, lower- extremity or scrotal edema, venous insufficiency.
• Pathology shows a firm grayish fibrosis, beginning at the level of the lower lumbar vertebral bodies and extending cranially to the renal hilum and caudally into the pelvis.
• Caudally the process can extend in the parailiacal and periureteral direction and involve the gonadal vessels, uterus, bladder, sigmoid colon and seminal vesicles.