Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

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surgery is bilateral renal cell carcinomas. Because of its high spatial resolution, intraoperative US is very useful in such a setting to better define indeterminate lesions, revealing more extensive or satellite lesions and establishing tumor margins. Intraoperative US and frozen section biopsy may spare the patient a nephrectomy.

Successful tumor enucleation implies that a tumor has a discrete border (i.e., has a pseudocapsule). Such a pseudocapsule is best defined by T2-weighted MRI and dynamic T1-weighted MRI.

Lymphadenectomy is indicated for patients with enlarged lymph nodes or a large tumor but without distant metastases and,in general,those tumors believed to be curable. On the other hand, the vast majority of patients with lymph node involvement already have additional, mostly multifocal metastases, and thus extensive lymph node dissection on a routine basis as part of a radical nephrectomy appears to have a limited effect on survival (node dissection is useful, however, for staging).

Similar to other malignancies, a postoperative imaging study is useful in establishing a baseline for detecting future tumor recurrence. Invariably, the underlying anatomy is distorted at surgery. At times imaging after a nephronsparing operation reveals a pseudotumor; these

tumors have round contours and enhance with contrast, resolving eventually except for a small cortical scar.

An occasional solitary metastasis is resected. Pulmonary resection for metastatic renal cell carcinoma is viable therapy for some selected slow-growing tumors.

Tumor Embolization

Need for a definitive diagnosis prior to tumor embolization or ablation therapy is obvious, yet a number of benign tumors have undergone needless therapy before a diagnosis is established. This problem appears more acute in the kidney than the liver and often revolves around nonfat-containing angiomyolipomas.

Tumor embolization is performed both as a stand-alone procedure and preoperatively. Embolization of extensive renal cell carcinomas decreases blood loss and simplifies surgery (Figs. 10.23 and 10.24). Some patients develop spontaneous renal vein-to–portal vein anastomoses, and such anastomoses need be considered prior to embolization. Aside from embolization, selective angiography aids in planning a nephron-sparing operation.

Embolization in a setting of tumor thrombus in the renal vein or inferior vena cava carries a potential risk of distal tumor embolization. A

suprarenal inferior vena cava filter minimizes this risk.

A major role for tumor embolization is palliation of hemorrhage or pain in inoperable patients. Superselective embolization of inoperable renal tumors is occasionally performed in patients with a solitary kidney; insufficient data preclude drawing any firm conclusions about the validity of such an approach.

Other Ablation Therapy

Laparoscopic cryoablation of small renal tumors is feasible (61); the efficacy of such therapy is incompletely studied.

Percutaneous injection or coagulation therapy of renal neoplasms has lagged similar counterparts in the liver. More than in most other organs, renal neoplasm therapy has remained in the province of the urologist and generally intraoperative US guidance is used.

Feasibility of percutaneous image guided radiofrequency ablation of renal cell carcinomas has been established in poor surgical risk patients (62). Interactive MR image guided radiofrequency interstitial thermal ablation of renal cell carcinomas is a new field. A low field strength unit monitors until the tumor is

replaced by a hypointense zone, identified on T2-weighted images acquired intermittently during ablation. Preliminary results are encouraging (63). One reported complication is skin metastasis at the electrode insertion site. Isolated local recurrences after radical nephrectomy are also amenable to radiofrequency ablation (64). Contrast enhanced CT immediately after ablation detects residual viable tumor. US identifies a hyperechoic interface at the junction of normal renal parenchyma and frozen tissue.

Therapy for Bilateral Tumors

Conservative surgery, such as heminephrectomies, is the initial consideration for bilateral and synchronous renal cell carcinomas. Occasionally bilateral nephrectomy and chronic dialysis is the only viable option, in which case renal transplantation should be considered.

Recurrence/Follow-Up

Renal carcinoma metastases more often are of a higher grade of malignancy than the primary rather than of a lower grade. Thus prognosis in patients with metastatic disease is based both

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on primary tumor grade and on that of the metastases.

A small tumor detected on a postcancer resection imaging study is generally considered to be a recurrence or a new cancer (assuming it was not evident on preresection imaging). The presence of small synchronous renal cell carcinomas and an increased prevalence of metachronous cancers suggest that serial imaging surveillance, possibly on an annual basis, of residual ipsilateral renal tissue (if any) and the contralateral kidney is indicated.

Initially most lung metastases are asymptomatic and are detected by screening. Bone metastases, on the other hand, become symptomatic early on. Chest follow-up is with either chest radiograph or CT, with proponents advocating either one or the other. Certainly CT is more sensitive in detecting metastases both in the chest and adjacent bones (assuming bone windows are used) and more often detects the rare solitary and resectable lung metastasis. On the other hand, CT also detects benign incidental nodules, often leading to unnecessary biopsy.

Currently CT is the study of choice to detect abdominal recurrence. Ultrasonography is less sensitive than CT. Magnetic resonance imaging is rarely employed for primary screening, although preliminary evidence suggests that it is equal, if not superior, to CT in tumor detection. It has a role in select patients, such as those with an iodine allergy. Nuclear scintigraphy requires separate scanning for bone, liverspleen, etc. Nuclear scintigraphy is currently the examination of choice in detecting bone metastases, but whether serial scans are beneficial in the absence of bone symptoms is debatable, and they are not often employed.

Rarely, a metastasis regresses spontaneously. Thus spontaneous regression of pulmonary metastases does occur. One should realize, however, that not all lung tumors in a patient with known renal cell carcinoma are metastases.

Prognosis

Based on tumor recurrence patterns, one recommended follow-up schedule is based on tumor stage: patients with stage T1 carcinoma are evaluated yearly clinically, those with stage T2 disease also have an annual chest radiograph and abdominal CT every 2 years, while those

with stage T3 disease undergo abdominal CT every 6 months for the first 2 years (65).

A nephrectomy in the presence of metastases is often justified as an attempt to prolong life or improve quality of life. A cure even after resection of a solitary metastasis is not common.

Sites of Metastases

Renal cell carcinoma is unpredictable in its spread, and metastases develop to unusual sites. Most common are metastases to the lungs and bone. Metastasis to the pancreas is not rare, in spite of statements to the contrary by some authors. Some metastases are already evident at the time of initial cancer diagnosis; in fact an occasional metastasis is detected and resected even before the primary tumor site is discovered.

Spread to the adrenal glands is by either direct extension or metastasis. Direct adrenal invasion is uncommon by a superior pole tumor less than several centimeters in diameter. Some of these metastases are from a contralateral kidney, presumably hematogenous in nature.

Unlike transitional cell carcinomas, metastasis along the ipsilateral ureteral stump following a previous radical nephrectomy is rare for renal cell carcinomas.

Resection of liver metastasis is often feasible, especially with a single focus, with prolongation of survival but at a cost of a high mortality rate.

Late Recurrence

Late recurrence is arbitrarily defined as 10 years or longer postnephrectomy. Tumor recurrence years after initial therapy suggests that use of a 5-year survival time frame is too short for this tumor. Renal cell carcinoma can recur years after nephrectomy.Anecdotal reports abound of pulmonary, pancreatic, and other metastases developing many years after nephrectomy. In general, prognosis is better in those with late rather than early recurrence.

Cystic Carcinomas

About 10% of all renal cell carcinomas are cystic. Complicating the picture is that more often a solid renal cell carcinoma is associated with an incidental cyst close by, such as a simple

cyst or acquired cystic disease of the kidney. The solid component of most cystic carcinomas is located close to underlying renal parenchyma. Rarely, a carcinoma arises from the outer surface of what appears to be a simple cyst.

Cystic carcinomas are classified into several patterns: multilocular, unilocular, necrotic, and those originating in the wall of a simple cyst; histopathologically, multilocular carcinomas can be divided into macrocystic and microcystic. Macrocystic tumors appear multilocular on US and contrast-enhanced CT; angiography reveals neovascularity in most tumors. When first detected, most multilocular cystic renal cell carcinomas already have a significant cystic component. When small, however, imaging shows them to be solid, although histology of resected specimens does reveal a microcystic component. On precontrast CT, microcystic tumors range from hypodense to hyperdense depending on the amount of hemorrhage. They exhibit slight CT contrast enhancement, are hyperechoic, and do not appear cystic on US; MRI reveals high signal intensities on both T1and T2-weighted images, and dynamic enhancement shows an irregular contrast enhancement pattern. Angiography of these small tumors typically shows little evidence of neovascularity.

Unilocular carcinomas consist of a cystic tumor containing either an irregular wall or mural nodules, detected by contrast-enhanced CT and US. Necrotic tumors range from anechoic to varying echogenicity, while their CT appearance varied from cystic with mural nodules to an irregular tumor. Neovascularity is common in viable tumor surrounding necrotic regions.

US using Levovist enhanced pulse inversion harmonic imaging shows that the thick wall of both cystic renal cell carcinomas and complex inflammatory cysts has intense contrast enhancement during the arterial phase (66).

Larger cystic renal cell carcinomas tend to have a complex cystic imaging appearance. In general, a cyst with a thick or irregular wall, prominent septa, wall calcifications, septations, or associated with an adjacent soft tissue component suggests a malignancy. Nevertheless, overlap occurs between benign complex cysts and cystic malignancies, and tumor identification is difficult. Temporal changes occur in some of these tumors. As an example,

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a simple renal cyst was resected; 1 year later numerous cysts encased the kidney, with cyst walls lined by a single layer of cuboidal epithelium (67). The degree of differentiation argued against a carcinoma and suggested a cystic mesothelioma, cystic lymphangioma, or even a multicystic dysplastic kidney, yet the tumor recurred repeatedly, invaded bowel, and became almost solid.

Aspiration cytology tends to be negative with cystic neoplasms, and a negative aspirate is of limited significance. A number of cystic carcinomas yield clear fluid, but this finding cannot be relied on. Comparing fluid aspirated from benign renal cysts and cysts containing a carcinoma, interleukin-6, basic fibroblast growth factor concentrations, and epidermal growth factor levels tend to be higher in malignant cysts.

Laparoscopic biopsy, followed by open resection is an option for complex cysts suspicious for cancer.

Prognosis is similar both for solid and cystic carcinomas.

Chromophil (Papillary) Adenoma

and Carcinoma

Renal papillary adenomas are common renal epithelial neoplasms; most are in the several millimeter size range. Papillary renal cell carcinoma is the second most common carcinoma of the renal tubules. These neoplasms manifest an adenoma-to-carcinoma evolution, and a continuous tumor spectrum ranging from papillary adenoma to papillary carcinoma is encountered. Synchronous papillary renal adenomas and carcinomas occur. Several families of a hereditary papillary renal cancer syndrome are reported.

These tumors tend to be multifocal and bilateral. They have specific immunohistochemical and genetic features distinct from other renal carcinomas.

Detected papillary renal cell carcinomas tend to be large, well-defined, and relatively hypovascular, and tend to enhance less with CT contrast than do clear cell tumors. Some exhibit occasional short intratumoral contrast-related stranding. Computed tomography revealed nine of 10 papillary renal cell carcinomas to be rounded, well-circumscribed, and sharply mar-

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ginated tumors containing central hypodense regions representing necrosis, surrounded by viable tumor seen as contrast-enhancing serpiginous tissue (68). An occasional cystic tumor contains multiple nodules. Some are associated with cholesterol necrosis and these tumors mimic an angiomyolipoma (69).

Although US detects fewer papillary tumors than CT, it aids in evaluating any cystic component.

Papillary renal tumors tend to be hypointense on T2-weighted images, often due to hemosiderin, hemorrhage, and necrosis, although hypointensity in some appears to be intrinsic to the papillary component.

These tumors often pose a diagnostic dilemma because of their benign appearance.

Chromophobe Carcinoma

A chromophobe renal carcinoma is considered a subtype of renal cell carcinoma exhibiting a low chromosome number. Histology reveals a mix of clear cells containing lipid and glycogen and eosinophilic cells.

These carcinomas occur in childhood. Prognosis is considerably better than with conventional renal cell carcinomas.

These tumors range from hypovascular to avascular. A minority of chromophobe carcinomas contain a central scar.

Duct of Bellini Carcinoma

Carcinoma of ducts of Bellini, or collecting duct carcinoma, originates from ducts of Bellini epithelium in the distal tubules located in the renal medulla. The prevalence is about 1% of all renal carcinomas.

Whether this tumor should be classified as a separate carcinoma or is a variant of a renal cell carcinoma is not clear. Histologic differentiation from a more common renal cell carcinoma is difficult, although morphologically, immunochemically, and cytogenetically it can be defined as a separate entity. Chromosome analysis suggests that molecular development of this neoplasm is different from that of a more common renal cell carcinoma. Specific tumor-suppressor genes appear to be involved in its pathogenesis. Embryologically,collecting ducts originate from the wolffian duct system, similar to renal calyces and ureters, and a point can thus be made of a

relationship of this tumor with transitional cell carcinomas.

This rare, aggressive neoplasm manifests in a younger population than the more common clear cell carcinoma. It develops in children. Hematuria is a common presentation. Some patients have positive urine cytology. It is not uncommon to find metastases at the time of first presentation.

Because duct of Bellini carcinomas originate predominantly centrally in the medulla, they tend not to deform the renal outline, a finding distinguishing these tumors from more common renal cell carcinomas. Imaging shows a solid, hypodense, and hypovascular or even avascular renal tumor with limited contrast enhancement. They tend to protrude into the central sinuses.

Oncocytoma

Clinical

Some authors classify oncocytomas as a type of renal adenoma. Epithelial oncocytes have a granular eosinophilic cytoplasm rich in mitochondria. These cells are not limited to oncocytomas but are also found in granular cell carcinomas (oncocytic adenocarcinomas) and some clear cell adenocarcinomas. Oncocytomas occur in several organs, but most often are found in kidneys. Mitochondrial DNA analysis suggests that a specific mitochondrial DNA alteration is responsible for oncocytomas.

Renal oncocytomas are more common in some families. These tumors are often detected incidentally in asymptomatic individuals; some are multiple and bilateral, with a rare patient having hundreds of nodules scattered throughout both kidneys.

Renal oncocytomas are probably benign tumors consisting primarily of oncocytic cells. They appear to originate from the cortical part of collecting tubules. Their prevalence is difficult to gauge because some have been misclassified as renal cell carcinomas or chromophobe carcinomas. Especially in the older literature an occasional one has been reported to metastasize, but whether these are misclassified is difficult to gauge.

Percutaneous biopsy or cytology tends to be misleading because some oncocytomas mimic a granular renal cell carcinoma. On the other

hand, a biopsy or aspiration cytology from a region rich in oncocytes may not detect an adjacent focus of carcinoma unless extensive sampling is performed. Pathologically, a diagnosis of an oncocytoma is one of exclusion by eliminating other, more ominous, tumors.

An occasional renal oncocytoma ruptures. Adjacent fat next to such a ruptured oncocytoma can mimic an angiomyolipoma.

Imaging

Oncocytomas are solid, homogeneous, wellmarginated, and often large tumors. They have no specific imaging findings; CT, US, and MR simply reveal a solid, well-marginated tumor. Especially when small, their imaging appearance is indistinguishable from that of renal cell carcinomas. In distinction to renal adenocarcinomas, necrosis and hemorrhage are not common, although larger oncocytomas tend to contain a central stellate scar that mimics the necrosis seen in a renal cell carcinoma. Cystic changes and calcifications are rare. They tend to be somewhat hypervascular. In general, imaging can suggest an oncocytoma but will not differentiate it from a renal adenocarcinoma.

Oncocytomas are hypointense on T1weighted MR images but vary in intensity on T2-weighted images. About half have a welldefined capsule. Post-MR contrast a minority of oncocytomas reveal a “spoke-wheel” enhancement pattern. These MR findings do not exclude a renal cell carcinoma.

Urothelial Tumors

Papilloma

Papillomas are transitional cell epithelial tumors that are difficult to classify. Histologically, differentiation from a low-grade transitional cell carcinoma is difficult, and controversy exists about whether they are indeed a separate benign entity or whether they represent a spectrum of transitional cell carcinomas. They are rare in the upper urinary tract. A male predominance is evident.

The even rarer upper urinary tract inverted papillomas are of uncertain malignant potential. Etiology of this proliferative tumor is unknown, and histopathologic diagnosis difficult. Of note is that some inverted papillomas

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precede, are synchronous with, or are metachronous with a malignant urothelial tumor, and thus the discovery of one requires a search for other urinary tract tumors.

The imaging appearance of papillomas is similar to that of other urothelial neoplasms. They range from sessile to pedunculated. The differential diagnosis includes transitional cell carcinoma, blood clots, a fungus ball, calculi, fibroepithelial polyp, and malacoplakia.

Local excision appears sufficient for these tumors.

Transitional Cell Carcinoma

Clinical

Urothelial origin malignant neoplasms include transitional cell carcinoma, squamous cell carcinoma, and adenocarcinoma. Of these, transitional cell carcinomas predominate and, after renal cell adenocarcinomas, represent the second most common renal neoplasm in adults. A minority contain a squamous cell metaplasia component. A rare transitional cell carcinoma contains a sarcomatoid component. Data from the Dutch hereditary nonpolyposis colorectal cancer registry suggest that patients with hereditary nonpolyposis colorectal cancer are at an increased risk of developing upper urinary tract transitional cell carcinomas (70).

Among transitional cell carcinomas originating in renal collecting systems, roughly one quarter are in an upper calyx, one quarter in a lower calyx, one quarter in renal pelvis, about 5% in a middle calyx and the rest are more extensive; in the ureters, slightly under 10% are in the upper segment, 20% in the middle, slightly under 50% in the lower segment, and 20% in the distal ureteral. A rare patient has the entire ureter affected. A number of reports describe a ureteral stump transitional cell carcinoma developing years after a nephrectomy for a benign or malignant condition.

The most common clinical finding with these tumors is intermittent hematuria, followed by flank pain. Ureteral obstruction and a nonfunctioning kidney develop eventually and thus a need for retrograde pyelography. A rare obstruction leads to ureteral rupture.

While positive cytology is obviously diagnostic, negative cytology does not exclude a transitional cell carcinoma. Especially with intrarenal