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1 Both authors: Department of Radiology, New York University Medical Center, Tisch HW 202, 560 First Ave., New York, NY 10016.
Received August 1, 2000;
accepted after revision October 6, 2000.
Address correspondence to C. M. Slywotzky.
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MATERIALS AND METHODS. Localized cystic disease was diagnosed in 18 patients on the basis of a review of imaging studies, clinical histories, and pathologic proof in four of the 18 patients. Average age at diagnosis was 54 years (age range, 24-83 years). Fifteen of the patients (83%) were men. CT was performed on 18 patients, sonography on nine, excretory urography on six, arteriography on four, and MR imaging on two.
RESULTS. Localized cystic disease was unilateral in all patients and characterized by multiple cysts of various sizes separated by normal (or atrophic) renal tissue in a conglomerate mass suggestive of cystic neoplasm. In some patients, involvement of the entire kidney, which was suggestive of unilateral autosomal dominant polycystic kidney disease, was seen. No cysts were seen in the contralateral kidney in 14 patients, and only one or two scattered small cysts were present in four patients. Clinical presentations included hematuria, flank pain, palpable abdominal mass, and localized oystic disease as an incidental finding. None of the patients had a family history of autosomal dominant polycystic kidney disease. Ten patients underwent follow-up (follow-up range, 1-12 years); nine patients underwent imaging follow-up and one patient underwent clinical follow-up, which showed stability of disease. Four patients underwent nephrectomy for suspected renal neoplasm.
CONCLUSION. Familiarity with localized cystic disease of the kidney and its imaging findings is important to avoid unnecessary surgery and to differentiate the disease from autosomal dominant polycystic kidney disease.
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Pathologic findings reviewed included descriptions of the appearance of the gross specimen, extent of involvement of the kidney by cysts, cyst contents, gross appearance and microscopic composition of cyst walls, microscopic composition of tissue between cysts, and gross and microscopic appearance of the uninvolved portions of the kidney.
All patients were examined with CT, nine with sonography, six with excretory urography, two with MR imaging, and four underwent arteriography. CT scans were performed using thin-section (5 mm) technique through the kidneys before and after IV contrast medium administration. Eleven patients underwent this dedicated renal protocol CT on initial examination, as did all nine patients who underwent CT follow-up. In seven patients the initial examination was performed only after IV contrast medium administration because no renal abnormality was suspected. In four of these patients, 10-mm sections were used.
MR sequences included half-Fourier acquisition single-shot turbo spin echo (HASTE) (TR/TE, infinite/62; flip angle, 120°). Axial two-dimensional spoiled gradient-echo images (fast low-angle shot) (TR range/TE, 120-200/4.4; flip angle, 70-90°) were obtained before and after injection of 0.1 mmol/kg of body weight of gadopentetate dimeglumine (Magnevist; Berlex Laboratories, Wayne, NJ). Coronal maximum-intensity-projection images were obtained from three-dimensional fat-suppressed gradient-echo sequences (4.2/1.3; flip angle, 12°) performed in the arterial phase after injection of gadopentetate dimeglumine.
Patient clinical profiles included age at presentation, sex, presence or absence of family history of renal disease, presenting symptoms, years of follow-up, and types of intervention performed.
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Clinical Features
Fifteen patients (83%) were men and three were women. The median age at
diagnosis was 50 years (age range, 24-83 years). On the basis of the imaging
findings, 12 patients were initially suspected of having a renal neoplasm,
three were suspected of having autosomal dominant polycystic kidney disease,
and three patients were diagnosed as having localized cystic disease as an
incidental finding. A variety of clinical presentations were seen. Five
patients presented with hematuria, four with flank pain, and one with a
palpable abdominal mass. Localized cystic disease was seen as an incidental
finding in eight patients. There was no family history of autosomal dominant
polycystic kidney disease in the 14 patients for whom this data was available.
Four patients underwent nephrectomy with pathologic proof at other
institutions, which was obtained for review. Nine patients had follow-up
imaging findings available from a 1- to 12-year period (average, 7 years).
Lesions in five of the nine patients showed complete radiographic stability
and lesions in four patients showed an increase in size in the kidney involved
by localized cystic disease. Symptoms of discomfort prompted cyst aspiration
in two patients and "unroofing" of a dominant cyst in one patient.
One patient without imaging follow-up is clinically stable 6 years after
diagnosis. Four patients with characteristic CT findings were lost to
follow-up after initial diagnosis.
Pathology
Four patients underwent nephrectomy at other institutions for suspected
renal neoplasm. In three patients, a conglomerate of cysts of various sizes
involved the kidney segmentally. Cysts showed no encapsulation and pathology
showed cysts of various sizes lined by flattened epithelium. On cross-section,
cysts contained clear yellow fluid and smooth walls without evidence of tumor
or papillary formation with regions of attenuated normal or atrophic renal
tissue separating the cysts. The fourth patient, a 24-year-old man, underwent
nephrectomy after 6 years of CT imaging surveillance. Increasing cyst size and
development of hyperattenuating cysts, which were probably related to trauma,
prompted the decision for surgical intervention because of concern about a
potential indolent neoplastic process. In this patient, pathologic evaluation
showed conglomerate cysts separated by normal (but attenuated) renal tissue
involving the upper and lower poles of the kidney. Walls of the numerous cysts
were smooth and glistening, but some exuded thick greenish brown fluid
containing hemosiderin consistent with prior hemorrhage. No areas of
calcification, induration, or papillary formation were seen. Uninvolved
portions of the kidney were normal in all patients. In all four patients, the
gross and histopathologic appearances of the cystic areas did not differ from
changes seen in autosomal dominant polycystic kidney disease.
CT Findings
CT findings of all patients were believed to be characteristic of localized
cystic disease of the kidney on the basis of the pattern of multiple simple
cysts of various sizes separated by normal (or atrophic) renal tissue in a
conglomerate mass (Figs.
1A,1B,1C,1D,2A,2B,2C,2D,3A,3B,3C,3D,4).
Localized cystic disease was unilateral in all patients. The extent of
involvement of the affected kidney varied considerably
(Table 1). Involvement of the
entire kidney was seen in six patients and, in these patients, localized
cystic disease was more likely to be confused with autosomal dominant
polycystic kidney disease (Fig.
3A,3B,3C,3D).
In the remaining 12 patients, only part of the kidney was involved, with a
polar predilection in most patients (n = 10) that extended to involve
the middle portion of the kidney (Figs.
1A,1B,1C,1D,
2A,2B,2C,2D,
and 4). One patient had upper
and lower pole involvement with sparing of the mid portion of the kidney. In
one patient only the upper pole was involved. Associated imaging findings
included scattered calcifications of cyst walls seen in four patients (Figs.
2C and
2D). It should be noted that
hyperattenuating cysts were seen in only one patient and were probably
associated with trauma. The contralateral kidney was entirely normal with the
exception of an atrophic kidney of uncertain etiology in one patient; and in
four patients, who were all older than 45 years, one or two scattered, small,
simple cysts (1-2 cm) were seen (Fig.
3C).
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Excretory Urographic and Arteriographic Findings
Excretory urography performed in six patients showed mass effect causing
distortion of the collecting system. Arteriograms in three patients showed
avascular masses with some stretched attenuated vessels, but no evidence of
neovascularity and normal vasculature in the uninvolved portions of the
kidney.
Renal Sonographic Findings
Renal sonography was nonspecific showing cystic masses, which appeared
complex because of the intervening attenuated normal parenchyma simulating
septae.
MR Imaging Findings
MR imaging was performed with gadolinium enhancement. In one patient with
involvement of the entire right kidney by localized cystic disease (Fig.
3A,3B,3C,3D),
multiple simple cysts were separated by attenuated, enhancing renal
parenchyma. Corresponding MR arteriography showed a slightly attenuated right
main renal artery with splaying of the intrarenal vessels around multiple
cysts (Fig. 3D). MR imaging
provided somewhat more facile visualization of the findings, especially when
viewed in the coronal plane. In the second patient evaluated with MR imaging,
involvement of the kidney was less extensive and findings paralleled those of
the corresponding CT. No evidence of enhancing tumor tissue was seen.
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Autosomal dominant polycystic kidney disease is one of the most common genetically transmitted diseases [12]. In humans, at least two chromosomal loci have been implicated in the pathogenesis of autosomal dominant polycystic kidney disease: the PKD1 locus mapped on chromosome 16 [14, 15] and PKD2 locus on chromosome 4 [16]. The renal cysts in autosomal dominant polycystic kidney disease are bilateral and involve both the cortex and the medulla, but autosomal dominant polycystic kidney disease can have an asymmetric onset, particularly in children [17,18,19]. Therefore, in certain cases, unilateral, nonprogressive localized cystic disease and multiple simple cysts may cause difficulty in differential diagnosis. The only way to resolve this diagnostic problem is to perform long-term follow-up and to obtain a family history, including imaging screening of family members.
Autosomal dominant polycystic kidney disease is not limited to renal manifestations with development of renal insufficiency, it is also associated with cysts in other organs (e.g., liver, pancreas) and the occurrence of cerebral aneurysms in a small percentage of affected patients [12]. The presence of hepatic cysts, which can be of various sizes, supports the diagnosis of autosomal dominant polycystic kidney disease occuring in approximately 57% of affected patients [20]. None of these extrarenal manifestations were present in our patients, nor was there any evidence of family history of autosomal dominant polycystic kidney disease in the 14 patients from whom this information could be obtained. Hyperattenuating cysts, which are a common finding in autosomal dominant polycystic kidney disease, were seen in only one patient in our series and, in that patient, a history of significant trauma was elicited. Nephrolithiasis is also a common renal manifestation of autosomal dominant polycystic kidney disease but was not observed in our patients.
Involvement of an entire kidney in patients with localized cystic disease may raise the possibility of autosomal dominant polycystic kidney disease (Fig. 3A,3B,3C,3D). However, no cysts (or occasionally 1-2 small cysts) (Fig. 3C) may be present in the opposite kidney in patients with localized cystic disease without other manifestations of autosomal dominant polycystic kidney disease. In one patient in our study, the cyst in the uninvolved kidney increased in size from 1 to 3 cm over a 12-year period. The patient was 61 years old at initial presentation and growth of simple cysts would not be unusual in this age group. This patient also showed an increase in cyst size in the kidney involved by localized cystic disease, as did three other patients.
The pathogenesis of localized cystic disease is unknown but may represent an acquired condition [13]. As with our cohort of patients, there appears to be a male predilection in case described in the literature and gross and histopathologic similarity to autosomal dominant polycystic kidney disease in the pathologically proven cases [8]. Localized cystic disease is characterized by replacement of various amounts of one kidney by multiple cysts. These cysts may be scattered diffusely throughout the kidney or involve a more localized portion of the kidney. Therefore, the radiographic findings depend on the number and size of the cysts and the amount of normal renal parenchyma between the cysts. In either form, no distinct encapsulated renal mass is formed. It is this finding that is crucial in distinguishing localized cystic disease from a focal cystic mass such as multilocular cystic nephroma or cystic carcinoma (Fig. 5).
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CT or MR imaging best reveal the salient imaging characteristics of localized cystic disease. However, the entire lesion must be systematically evaluated on multiple contiguous sequential images. Although a select single axial image of localized cystic disease may potentially be confused with cystic neoplasm (Fig. 1D), systematic evaluation of multiple sequential axial images should enable differentiation on the basis of the presence of a continuum of adjacent cysts (Fig. 1A,1B,1C,1D) rather than a focal encapsulated loculated mass (Fig. 5). These variably sized cysts are separated by normally enhancing renal parenchyma (Figs. 1A,1B,1C,1D,2A,2B,2C,2D,3A,3B,3C,3D,4). The parenchyma may become quite attenuated depending on the size and proximity of the neighboring cysts and can be misinterpreted as enhancing septae (Fig. 1D). However, unlike multilocular cystic nephroma or cystic neoplasm (Fig. 5), localized cystic disease shows no discrete encapsulation and, in fact, often shows other cysts nearby that are clearly separate from the main conglomerate mass of cysts.
In the two patients examined with MR imaging, the features of localized cystic disease were somewhat easier to delineate given the ability to display the lesion in multiple planes. However, the diagnosis is also made with meticulous examination of sequential axial CT images. Multidetector CT scanners also provide multiplanar capabilities. Whichever modality is used, it is the understanding and appreciation of the underlying features of localized cystic disease of the kidney that will allow accurate interpretation.
A thick fibrous capsule typically encapsulates multilocular cystic nephroma and causes compression of adjacent renal parenchyma [21,22,23]. This thick capsule encases multiple fluid-filled noncommunicating locules separated by septae. The interlocular septae may contain fibrous tissue or embryonic tissue but are devoid of renal parenchyma. Because of the difficulty of differentiating multilocular cystic nephroma from cystic Wilm's tumor and multicystic renal cell carcinoma on the basis of imaging findings, surgery is indicated in all of these conditions.
Localized cystic disease is not associated with renal insufficiency [20]. Interestingly enough, even in patients in whom a large portion of the kidney is replaced by cysts (Fig. 3A,3B,3C,3D), contrast medium excretion from the affected kidney on CT or MR imaging appears symetric to that seen in the normal kidney. These features also differentiate localized cystic disease from a multicystic dysplastic kidney, which can be seen in an adult as a unilateral multicystic disorder. The multicystic dysplastic kidney is not functional, is usually associated with ureteral atresia or agenesis, and typically contains a central core of relatively solid dysplastic tissue with peripheral cysts [20]. This dysplastic core of tissue may enhance after IV contrast medium administration but has a different nephrographic appearance from that of normal renal tissue. The tissue between the cysts in localized cystic disease is normal (or atrophic) renal tissue rather than dysplastic.
In summary, localized cystic disease of the kidney (also referred to as segmental cystic or unilateral cystic disease) is an entity that needs to be recognized by radiologists as a benign, nonsurgical condition that requires periodic imaging follow-up. Greater awareness of this condition may provide more clues into its pathogenesis, and help prevent its confusion with cystic neoplasm, multilocular cystic nephroma, or autosomal dominant polycystic kidney disease, each of which has a different treatment approach and prognosis.
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