Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

any one tumor is not uniform, resulting in a heterogeneous appearance. Also regions of tumor necrosis do not lead to a signal loss.

Scintigraphy

Bone scintigraphy can be positive in a hypervascular clear cell renal neoplasm.

An FDG-PET scan detects most but not all renal cell carcinomas. Angiomyolipomas and some other tumors result in false-positive findings, and in renal cancer detection PET offers no significant advantage over other imaging modalities. Positron emission tomography depicts solid renal neoplasms as regions of increased uptake and cysts are seen as photopenic regions.

Staging

General

Stage is the most important prognostic factor in renal cell carcinoma patients. Two classification systems are in use for staging renal cell carcinomas: Robson staging system, more popular in the United States and somewhat simpler to use; and the tumor, node, metastasis (TNM) system (Table 10.6). Both suffer limitations to staging accuracy and both tend to understage more often than overstage.

Lymphatic spread of renal cell carcinoma during initial detection is about 10% or less; most affected patients have advanced stage disease, distant metastases, a large tumor, and poor survival.

Biopsy

In most instances a renal cell carcinoma is diagnosed with imaging, and a biopsy or aspiration cytology is not obtained prior to surgery. Even tumors with an atypical imaging appearance are generally investigated surgically. In particular for small, discrete lesions, the efficacy of aspiration cytology in determining tumor pathology is limited and has led to complications.

Currently the primary role for aspiration cytology is in a nonoperable patient where a tissue diagnosis needs to be established prior to alternative therapy or if metastases or lymphoma are suspected.

Imaging

Either a chest radiograph or chest CT is helpful in a search for metastases, although which of these two is preferred is debatable.

Currently helical CT is the primary staging modality used. How reliable is CT in staging renal cell carcinoma? A number of studies suggest that overall T-staging accuracy is only about 60% (58). Although of prognostic importance, the low CT sensitivity and specificity in detecting fat invasion is not crucial because perinephric fat is also resected during a nephrectomy for cancer and imaging detection of

KIDNEYS AND URETERS

Table 10.6. Tumor, node, metastasis (TNM) classification of primary renal cell carcinoma

Primary tumor:

Lymph nodes:

Nx Regional lymph nodes cannot be assessed. N0 No regional lymph node metastasis.

N1 Metastasis in a single lymph node

N2 Metastasis in more than one regional node

Distant metastasis:

Mx Distant metastasis cannot be assessed M0 No distant metastasis

M1 Distant metastasis

Note: Above classification applies to clear cell renal carcinoma, papillary renal carcinoma, chromophobe renal carcinoma, and collecting duct renal carcinoma.

Source: From the AJCC Cancer Staging Manual, 6th edition (2002), published by Springer-Verlag, New York, NY, used with permission of the American Joint Committee on Cancer (AJCC), Chicago, IL.

perinephric fat invasion does not influence surgery.

Dynamic MRA is an alternate in place of CT in a setting of severe renal dysfunction, extensive polycystic kidney disease, or a contraindication to iodinated contrast media. Potentially, MR could replace CT in staging these tumors. Compared to surgical and pathologic staging, MRI using T1-, T2-weighted, gadolinium

enhanced and time-of-flight sequences achieved good T and M staging, but was poor for N staging (59); MRI can readily assess venous invasion.

Both CT and MR detect adenopathy but cannot determine whether an enlarged node is secondary to inflammation or tumor. Some authors believe that CT staging accuracy for lymphadenopathy is close to chance (58). The role of MR in evaluating adenopathy and metastases continues to expand. Ultrasonography appears inferior in adenopathy detection.

A reasonable preoperative staging strategy in the occasional pregnant woman developing a malignant renal tumor consists of abdominal US and MRI to define local tumor extension and a chest radiograph to detect pulmonary metastases.

Either CT or MR is used to detect adjacent organ invasion. Bone scintigraphy has a limited role in initial tumor staging unless clinical or laboratory evidence suggests bone involvement.

Vascular Invasion

Even small carcinomas tend to invade adjacent renal vein branches, but extension as a tumor thrombus into the renal vein and inferior vena cava is uncommon for small tumors; the risk of invasion increases with tumor size, and venous extension to the right atrium is not uncommon with large tumors (Figs. 10.18 and 10.19). Obviously, detecting venous extension is important in planning resection. Imaging should also detect any anomalous vascularity. Angiography currently does not have a role in the staging of renal cell carcinomas but is occasionally performed to define blood supply and as a prelude to preoperative embolization (Fig. 10.20). Contrast CT and MRA have supplanted angiography’s role both in a search for renal vein invasion and in providing a vascular road map for the surgeon (Fig. 10.21).

Even small vessel invasion affects prognosis. One of the reasons is that a tumor thrombus contains more dividing cells than a primary tumor, that is, a tumor thrombus has a shorter tumor doubling time and thus is more aggressive, a conclusion reached by comparing the proliferation index of primary renal cell carcinomas and their corresponding neoplastic thrombi (60). Patients with renal cell carcinomas exhibiting microor macrovascular

KIDNEYS AND URETERS

Figure 10.20. Right renal cell carcinoma. Contrast filling and stretching of intrarenal vessels in a vascular tumor are evident. Metastases were also detected. (Courtesy of David Waldman, M.D., University of Rochester.)

invasion have a significantly worse prognosis than those without such invasion; prognosis also varies with the extent of vascular invasion. Detection of small vessel invasion is beyond the resolution of the current imaging modalities.

Figure 10.21. Transverse MR image reveals a left renal cell carcinoma with renal vein invasion (arrow). (Courtesy of Brian R. Herts, M.D., Cleveland Clinic Foundation.)

Figure 10.22. Coronal MR image identifies an intraluminal inferior vena cava filling defect defect (arrow) in a patient with a left renal cell carcinoma. (Courtesy of Brian R. Herts, M.D., Cleveland Clinic Foundation.)

Imaging can determine whether the inferior vena cava is simply compressed by an extrinsic tumor or whether a tumor extends intraluminally (Fig. 10.22). The extent of inferior vena caval involvement determines the type and complexity of the resection. To reduce blood loss, surgery in a setting of inferior vena cava invasion necessitates either direct caval clamping or the use of cardiopulmonary bypass. Imaging should thus identify whether a thrombus barely involves the vena cava, remains below most inferior hepatic veins, terminates between the hepatic veins and the diaphragm, or extends above the diaphragm and possibly into the right atrium. Contrast-enhanced imaging differentiates between a bland thrombus and a tumor thrombus. Invasion of the caval wall, although not common, is difficult to determine with imaging, which is unfortunate because invasion necessitates partial vena caval resection. MR is superior to both CT and US in detecting inferior vena cava tumor thrombi, although technically good CT is often adequate. CT tends not to identify the cephalad extent of a tumor thrombus.

Preoperative helical CT detects renal vein invasion with a sensitivity of >80% and a

specificity approaching 100%; reported sensitivity varies depending on whether small intrarenal venous thrombi are considered or not. False-positive results occur due to unopacified blood producing a flow void artifacts. Magnetic resonance imaging should detect all distal renal vein involvement; cavography should be considered if neither CT nor MR is satisfactory.

Ultrasonography identifies tumor venous extension as renal vein or inferior vena cava distention by echogenic material and decreased or absent flow in this segment, as detected by Doppler US. Tumors limited to the intrarenal veins account for some false-positive results. The current role of color Doppler US in detecting tumor venous extension appears to be in those patients with an incomplete or equivocal CT examination and unavailability of MR.

With a suspected carcinoma invading the inferior vena cava and possibly extending into the right atrium, transesophageal echocardiography is useful to establish the cephalad extent of a cavoatrial tumor and aid surgical management.

If needed, intraoperative US defines the extent of vena caval invasion. Ultrasonography may aid instrument placement and decrease the risk of tumor thrombus dislodgment.

Therapy

Controversy surrounds the therapy of small (<2cm) renal cell tumors of low malignant potential. In most patients these tumors are resected (often with a nephron-sparing resection), but in a high surgical risk patient an argument can be made for CT follow-up and resection only if tumor growth ensues. Conventional chemotherapy and radiotherapy are largely ineffective for renal cell carcinomas.

Medical Therapy

Interleukin-2 is a T-cell growth factor that also enhances natural killer cell function. Its preliminary use suggests a role in metastatic renal cell carcinoma. The response appears to be greater for metastatic foci rather than for the primary renal tumor, with an objective response rate of about 15% to 30% of patients. Tumor regression is achieved in up to one third of patients, with a complete response in an occasional one.

ADVANCED IMAGING OF THE ABDOMEN

Interleukin-2 was approved by the Food and Drug Administration in 1992 for treatment of metastatic renal cell carcinoma. The response to interleukin-2 therapy is difficult to evaluate with imaging due to residual deformity. 2-[18F]- fluoro-deoxy-D-glucose—PET imaging appears useful in these patients, but if interleukin-2 therapy is contemplated, a pretherapy scan aids in establishing a baseline.

Interferons, produced by the body in response to viral infections, also have an antitumor effect due to direct cytotoxicity and activation of a number of immunologic pathways. Both recombinant a-interferon and g- interferon, at times combined, have been used to treat metastatic renal cell carcinoma, although little data is available on the effect of interferon therapy on survival in patients with inoperable renal cell carcinoma. Preliminary results suggest prolonged survival in interferontreated patients.

Cimetidine blocks histamine-mediated activation of suppressor T-cells and appears to have antitumor immune properties. Anecdotal reports suggest a response in some patients treated with cimetidine for metastatic renal cell carcinoma.

Resection

Refinements in surgical technique have led to more conservative surgery such as enucleation and heminephrectomy. Current experience suggests that in selected patients conservative surgery is as effective as radical surgery.With an increasing number of small tumors detected incidentally, conservative (nephron sparing) surgery achieves good long-term results. Complicating the issue, however, is multicentricity of some small tumors. Also, an invasive growth pattern, high-grade nuclear atypia, and Bellini duct carcinomas are associated with a poor prognosis. Some surgeons believe that even with a localized renal cell carcinoma radical nephrectomy has a role; it has low morbidity, excellent local tumor control, and high survival. These surgeons maintain that for patients with a normally functioning contralateral kidney, no convincing evidence exists to justify a nephron-sparing operation on a routine basis. Nevertheless, laparoscopic wedge resection of smaller renal carcinomas is successfully performed. One indication for nephron-sparing