Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

KIDNEYS AND URETERS

parenchyma is detected. Why the loss of normal renal tissue is part of this condition is puzzling. Still, the kidneys are larger than normal.

Several criteria are used to identify patients at risk for developing adult polycystic kidney disease. One scheme is that the presence of at least two renal cysts (either unilateral or bilateral) in individuals at risk and younger than 30 years is regarded as sufficient to establish the diagnosis; in those 30 to 59 years of age at least two cysts in each kidney and in those above 60 years of age at least four cysts in each kidney are required. Ultrasonography can be used to screen for these cysts.

Computed tomography or MR is useful to evaluate for any associated liver disease.

The sensitivity of renal US in individuals under 30 years of age at risk for autosomaldominant polycystic kidney disease was 95% for those with PKD1 but only 67% for those with PKD2, but US sensitivity for either PKD type in individuals aged 30 years or older was 100% (22); DNA genetic linkage analysis was the gold standard.

These cysts vary from hypoto hyperintense both with T1and T2-weighted images, presumably due to prior hemorrhage (Fig. 10.3). A fluid-fluid level is identified in some.

Imaging

Initially cysts are small, but eventually imaging identifies bilateral enlarged kidneys, at times markedly asymmetrical, and containing multiple cysts. The cysts vary in size and distort surrounding parenchyma. Computed tomography shows most cysts to resemble simple cysts, although hemorrhage into cysts is common and these are hyperdense to water (Fig. 10.2). Some have a fluid–fluid level or even appear as a solid tumor. Renal calcifications are generally secondary to calculi, prior hemorrhage into a cyst, or cyst wall calcifications.

Figure 10.2. Polycystic disease. Transverse CT image through the kidneys reveals numerous cysts varying in size. Little renal parenchyma is left. (Courtesy of Patrick Fultz, M.D., University of Rochester.)

Therapy

Follow-up of these patients is generally by US. Computed tomography is useful to evaluate for a suspected complication. Intravenous urography has no role in follow-up.

Open transperitoneal bilateral renal cyst reduction surgery is an option in symptomatic patients; one advantage of this approach is that any liver cysts are also amenable to therapy. Laparoscopic cyst unroofing (decortication or marsupialization) for relief of pain is also an option; intraoperative US aids cyst detection during the laparoscopic procedure. Some of these patients require repeat cyst unroofing before pain relief is achieved.

A number of these patients eventually undergo renal transplantation. Some surgeons recommend nephrectomy prior to renal transplantation, although others disagree and reserve nephrectomy for those with intracystic hemorrhage, significant hematuria, pyonephrosis, or other complications.

Autosomal Recessive

Also known as Potter type I and infantile polycystic disease, the autosomal-recessive form of polycystic kidney disease manifests early in life. The underlying defect is renal tubular ectasia. The nephrons are normal. Expressivity varies, with some patients not surviving beyond the neonatal period. Those with milder renal involvement survive longer and develop hepatobiliary fibrosis and dilated bile ducts. Thus the severe form detected in infancy results primarily in renal involvement, called infantile polycystic disease, while in older children liver

KIDNEYS AND URETERS

size or remain stable with age; renal echogenicity approaches that seen in patients with autosomal-dominant polycystic kidney disease but without marked kidney enlargement.

Alport’s Syndrome

Alport’s syndrome is an inherited, degenerative disorder involving basement membrane collagen that lacks Goodpasture antigen. Both sex-linked dominant and autosomal-recessive forms are described. Electron microscopy– observed anomalies are almost specific for this syndrome. It is linked to Goodpasture’s disease, an uncommon autoimmune condition also showing a similar basement membrane collagen abnormality. In a broader context, this syndrome is linked to antiglomerular basement membrane disease and thin basement membrane disease, both diseases being more common than Alport’s syndrome.

Symptoms start in childhood. Hematuria and proteinuria eventually progress to renal failure.

Imaging identifies small, smooth kidneys with poor function.

Alagille’s Syndrome

Alagille’s syndrome, or arteriohepatic dysplasia, is discussed in more detail in Chapter 8. These patients also develop tubulointerstitial nephritis and renal tubular acidosis. An occasional manifestation is resultant renovascular hypertension.

Angiography reveals unior bilateral renal artery stenoses and abnormalities in the aorta and celiac superior mesenteric and subclavian arteries. Some patients develop bilateral renal cysts and aortic wall calcifications at an early age.

Glomerulocystic Disease

Both sporadic and familial glomerulocystic disease develop. The hallmark of this disease is dilation of Bowman’s space and proximal convoluted tubules. Numerous glomerular cysts develop but without dysplasia. Affected infants have enlarged kidneys. Liver cysts may be present.

Glomerulocystic disease associated with either hypoplastic or normal-sized kidneys is

found in older children and adults and probably represents an acquired type of glomerulocystic disease. Whether this is the same entity seen in infants is conjecture. In fact, glomerulocystic disease is probably much more common than the relatively small number of published cases suggest; in adults it may be asymptomatic and only becomes symptomatic when another condition, such as lupus glomerulonephropathy or hemolytic-uremic syndrome, is superimposed.

The diagnosis is suggested by renal biopsy, although histopathology is not always straightforward. In addition to glomerulocystic kidney disease, renal cysts are found in autosomalrecessive polycystic kidney disease, autosomaldominant polycystic kidney disease, and diffuse cystic dysplasia.

In the neonate, both polycystic diseases and glomerulocystic disease result in bilaterally enlarged hyperechoic kidneys. High-resolution US detects small, isolated cysts in a hyperechoic renal cortex, with these cysts usually being smaller than those found in typical autosomaldominant polycystic kidney disease. Also, these cysts extend to the periphery, but no cysts are seen in renal medulla, which distinguishes this condition from both autosomal-recessive and -dominant polycystic diseases.

Medullary Cystic Disease

Renal medullary cystic disease consists of a spectrum of abnormalities eventually leading to renal failure. These patients have progressive renal tubular atrophy. Two forms are described: a juvenile form (also called juvenile nephronophthisis) inherited as an autosomalrecessive trait manifesting in childhood, and an adult form inherited as an autosomal-dominant trait. A tubulointerstitial nephritis develops in both forms. Gross medullary cysts are found in the adult form, while smaller cysts develop in the juvenile form.

In the juvenile form US reveals increased echogenicity secondary to the small cysts. The corticomedullary junction is poorly differentiated. Urography shows decreased contrast excretion, and pyelography identifies tubular ectasia. Renal size tends to decrease with disease progression, and corticomedullary cysts became evident. These cysts are better defined with CT and MRI than with US.

Because US abnormalities appear before clinical symptoms or signs are evident, US is useful in screening suspected families.

Biopsy suggests the diagnosis.

Familial Glomerulosclerosis (Familial

Nephrotic Syndrome)

In the nail-patella syndrome, nail and skeletal abnormalities are associated with a nephropathy. Renal biopsy reveals glomerulosclerosis, and electron microscopy identifies massive fibrillar collagen within a mesangial matrix and basement membrane, a hallmark of this condition. Similar changes are also found in some patients with proteinuria and hematuria but without other stigmata of nail-patella syndrome. These patients have mild proteinuria early in life, and nephrotic syndrome becomes apparent during the second or third decade.

Tuberous Sclerosis

Tuberous sclerosis, or Bourneville-Pringle disease, is a neurocutaneous disorder having an autosomal-dominant inheritance, although spontaneous mutations also occur. Mental retardation and seizures are part of multiorgan involvement and renal lesions are common, consisting mostly of angiomyolipomas and cysts. Prevalence of lymphangioleiomyomatosis is also increased in tuberous sclerosis. Imaging in affected individuals begins to identify renal lesion during early childhood and most individuals have developed renal tumors by late childhood. Most common are angiomyolipomas, followed by simple renal cysts.

An occasional cyst disappears during followup but angiomyolipomas do not. Although generally believed that these patients are not at increased risk for renal cell carcinomas, anecdotal reports of renal malignancies abound.

An occasional patient has multiple cysts to the point of mimicking polycystic disease. Angiomyolipomas are prone to bleeding and forming hematomas. Eventually renal insufficiency and renal failure ensue if sufficient parenchyma is replaced by cysts and tumors. A rare first presentation is an elderly patient with gradual renal failure and imaging detecting marked bilateral renal parenchymal distortion due to multiple cysts and angiomyolipomas.

ADVANCED IMAGING OF THE ABDOMEN

Von Hippel-Lindau Disease

Von Hippel-Lindau disease is a hereditary cancer syndrome caused by mutations of the VHL tumor-suppressor gene, which is located on the short arm of chromosome 3. The VHL gene produces a tumor-suppressor protein, called pVHL, which plays a role in angiogenesis, cell cycle regulation, and other functions, and regulates both growth and differentiation of kidney cells. Mutations of the VHL gene are also found in mesotheliomas and small cell lung carcinomas. Nevertheless, the etiology of von Hippel-Lindau disease appears to be more complex than currently apparent because a germ cell mutation is identified only in 70% of affected patients. Also, systematic investigation of families of involved individuals often detects additional silent tumors.

This autosomal-dominant disease has agerelated penetrance of close to 100% at age 60 years. Affected individuals develop central nervous system hemangioblastomas, retinal angiomas, pancreatic cysts and islet cell tumors, adrenal pheochromocytomas and paragangliomas, epididymal cystadenomas, and in the kidneys cysts and clear cell carcinomas. Only a subgroup of these patients is at increased risk for developing a pheochromocytoma. Thus these patients are subdivided into type I (without pheochromocytoma) and type II (with pheochromocytoma).

Renal cysts are often multifocal and bilateral and are predominantly cortical in location. They do not progress to renal failure. There is, however, an increased prevalence of neoplasms in these cyst-containing kidneys. Multicentric renal cell carcinomas are common, at times bilaterally.

Among patients with von Hippel-Lindau disease having renal cell carcinomas, cancers occur 25 years earlier, are more often associated with renal cysts, and tend to be multifocal and bilateral, but have a lower grade histology and better 10-year survival than unselected patients with renal cell carcinoma (23); metastases occurred in von Hippel-Lindau disease patients only when tumors were >7cm in diameter. These tumors tend to be encased by a fibrous capsule.

The treatment of cysts and tumors in this disease has become rather conservative and differs from conventional therapy. Many asymp-

KIDNEYS AND URETERS

tomatic lesions are observed rather than resected, and CT, US, and MRI are used for screening, follow-up of known lesions, and overall management of these patients, keeping in mind that CT and especially US miss small tumors in these patients. A renal carcinoma is resected only when it has grown to a certain size. Over the last several decades surgery in these patients has evolved from radical nephrectomy to a nephron-sparing operation. A radical nephrectomy is reserved for larger or more numerous tumors; follow-up consists of CT, chest radiography, and renal function tests every 6 months.

These patients develop end-stage renal failure both from surgical therapy and from tumor growth. Theoretically, transplantation with its associated immunosuppression may predispose to tumor recurrence, but in practice this does not occur.

Sickle Cell Disease

The primary kidney abnormality in sickle cell disease is small vessel involvement leading to renal function impairment. The hemolysis these patients experience also results in glomerular hemoglobin deposition. Findings in other organs, primarily spleen, are common. Patients with heterozygous or homozygous sickle cell disease develop enlarged kidneys, focal infarcts, cortical necrosis, and progressive renal insufficiency.

Most teenagers with sickle cell disease have a normal renal US appearance, gradually developing either a focal or a diffuse increase in reflectivity in the renal medulla or throughout the kidney, changes similar to those seen in early nephrocalcinosis. Both RI and PI are increased, with findings directly related to disease severity.

With iron deposition, MR reveals hypointense signals from renal cortices on both T1and T2weighted images.

Hemophilia

Ultrasonography in hemophilia type A patients identifies smaller than usual kidneys and dilated calyces and renal pelves, at times containing blood clots. Calculi are common. The

overall appearance mimics that seen in chronic pyelonephritis.

Adjacent hematomas are secondary to retroperitoneal bleeding.

Beckwith-Wiedemann Syndrome

Beckwith-Wiedemann syndrome is a congenital overgrowth syndrome with a high sporadic occurrence, manifesting variable expressivity. There is a Beckwith-Wiedemann registry at the National Cancer Institute. Common abnormalities include macroglossia, abdominal wall defect, large birth weight, nephromegaly, and less often hemihypertrophy.

Affected children are prone to developing childhood solid tumors, including Wilms’ tumor, adrenocortical carcinoma, and hepatoblastoma. An occasional child has a sarcoma or renal cell carcinoma. One should keep in mind, however, that not all renal tumors in these patients are malignant. Benign renal abnormalities, consisting of renal cysts, caliceal diverticula, hydronephrosis, and nephrolithiasis, occur in approximately 25% of these patients; most patients are asymptomatic.

Bartter’s Syndrome

The rare Bartter’s syndrome leads to hypokalemia and increased plasma renin and angiotensin II levels. It should be suspected in a child with nephrocalcinosis and a history of polyhydramnios and premature delivery.

Renal US findings vary; US tends to reveal hyperechoic pyramids or diffuse hyperechoic kidneys.

Baseline scintigraphy in one patient was normal, but pharmacologic blockade of the renin-angiotensin system with captopril revealed a bilateral increase of parenchymal transit time, time to maximum activity, and retained cortical activity (24); the authors suggest captopril renography for differentiating Bartter’s syndrome from other causes of hypokalemia.

Tyrosinemia

A deficiency of fumarylacetoacetate hydrolase leads to tyrosinemia, an autosomal-recessive