IMAGING TEACHING CASE Localized Cystic Disease of the Kidney: An Unusual Entity That Can Mimic a Cystic Neoplasm

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1 IMAGING TEACHING CASE Localized Cystic Disease of the Kidney: An Unusual Entity That Can Mimic a Cystic Neoplasm Erik E. Dowden, MD, 1 Adeboye O. Osunkoya, MD, 2,3 and Deborah A. Baumgarten, MD, MPH 1 INDEX WORDS: Renal cyst; renal neoplasm; cystic renal neoplasm. INTRODUCTION The differential diagnosis for cystic kidney masses is extensive and includes both benign and malignant processes. In most cases, a combination of clinical history, laboratory data, and imaging can aid in limiting this differential. In the case that a specific diagnosis cannot be made, a lesion usually can be characterized as benign or malignant based on this information. Knowledge of the spectrum of cystic kidney masses and their clinical and radiologic presentations often can help avoid unnecessary kidney biopsy or surgery. We report a case of a benign cystic kidney entity with diagnostic imaging characteristics that aid in its differentiation from other malignant processes. CASE REPORT Clinical History and Initial Laboratory Data We report a case of a 24-year-old white man with right flank pain, hematuria, hypertension, and a cystic mass involving the lower right kidney. The patient had been evaluated by a community urologist and was referred to our institution for further evaluation. The patient s symptoms had a fairly recent onset, with right flank pain described as constant and radiating to the right inguinal region with intermittent exacerbations. The patient had no urinary frequency, intermittency, urgency, weak stream, or sexual dysfunction. He had no significant surgical, medical, or family history. The patient had no family history of polycystic kidney disease, tuberous sclerosis, or von Hippel-Lindau disease. Family members had undergone screening ultrasonography, with negative results for cystic disease. Results of the initial basic metabolic panel at our institution were normal: sodium, 138 meq/l (138 mmol/l); potassium, 3.9 meq/l (3.9 mmol/l); chloride, 104 meq/l (104 mmol/l); bicarbonate, 27 meq/l (27 mmol/l); anion gap, 7 meq/l (7 mmol/l); osmolality (calculated), 275 mosm/kg (275 mmol/kg); glucose, 97 mg/dl (5.4 mmol/l); serum urea nitrogen, 9 mg/dl (3.2 mmol/l); serum creatinine, 0.8 mg/dl (61 mol/l); and total calcium, 9.4 mg/dl (2.35 mmol/l). Complete blood cell count values were normal: white blood cells, / L; red blood cells, / L; hemoglobin, 14.3 g/dl; hematocrit, 40.0%; and platelets, / L. The patient had a history of intermittent gross hematuria; however, urinalysis at our facility was significant for only microscopic hematuria and urine protein excretion of 100 mg/dl. Urine protein was not quantitated. Specific gravity was Urine culture yielded no growth. Twenty-four hour urine collection showed a normal aldosterone level of 8.0 g/d, normal urine metanephrine level of 121 g/d, and normal normetanephrine level of 223 g/d. Serum renin was not measured. Imaging Studies A computed tomographic scan from an outside facility reportedly showed a large complex cystic mass involving the right kidney, which did not enhance after contrast. Unfortunately, the images and official report from this examination were not available. At our institution, the patient underwent ultrasonography, which showed a multiseptated mass in the lower right kidney (Fig 1). There were no calculi and no increased vascularity associated with this mass on Doppler images. The left kidney was normal. Magnetic resonance imaging (MRI)/magnetic resonance angiography showed a complex multiloculated nonencapsulated lesion that extended from midkidney into the lower pole (Fig 2). The lesion measured cm in the anteroposterior by transverse and craniocaudal dimensions and protruded into the pelvis of the right kidney with mass effect on the proximal right ureter, resulting in mild right-sided pelvicaliectasis. The multiple cysts did not enhance after gadolinium, and normal-appearing kidney parenchyma was present between cysts. There were a few smaller simple cysts within the right kidney parenchyma separate from this lesion. Differential considerations given at that time included mul- From the Departments of 1 Radiology, 2 Pathology and Laboratory Medicine, and 3 Urology, Emory University Hospital, Atlanta, GA. Received April 15, Accepted in revised form August 20, Originally published online as doi: /j.ajkd on December 7, Because the feature editor recused himself, the peerreview and decision-making processes were handled without his participation. Details of the journal s procedures for potential editor conflicts are given in the Editorial Policies section of the AJKD website. Address correspondence to Deborah A. Baumgarten, MD, MPH, Emory University Hospital, Department of Radiology, 1365 Clifton Rd NE, Atlanta, GA dbaumga@ emory.edu 2010 by the National Kidney Foundation, Inc /10/ $36.00/0 doi: /j.ajkd American Journal of Kidney Diseases, Vol 55, No 3 (March), 2010: pp

2 610 Dowden, Osunkoya, and Baumgarten The gross specimen consisted of fragments of kidney tissue ranging from cm with a combined weight of 50.1 g. The tissue was described as containing multiple cysts with normal kidney parenchyma adjacent to and between the cysts (Fig 3). The cysts were subcortical, with sizes ranging from cm. The lining of the cysts was smooth and thin, with clear serous internal contents. No papillary or solid masses were present. The microscopic description was similar to that of multilocular cystic nephroma, with multiple simple cysts. However, note was made of normal kidney parenchyma between the cysts, not a feature of multilocular cystic nephroma. The final pathologic interpretation was benign multicystic lesion (simple cysts), negative for carcinoma. The patient recovered uneventfully. The pain, microscopic hematuria, proteinuria, and hypertension improved during the next 5 months. Follow-up computed tomography has shown a stable postoperative appearance with no recurrence or progression. Figure 1. (A) Longitudinal and (B) transverse greyscale images show multiple predominantly anechoic round lesions within the lower pole of the right kidney. Several lesions have thin septations. Normal parenchyma is noted between several lesions (arrow). (C) Longitudinal color Doppler image shows no significant flow within the cystic area. tilocular cystic nephroma and low-grade cystic renal cell carcinoma. Diagnosis Localized cystic disease of the kidney. Clinical Follow-up Conservative attempts at pain relief were unsuccessful. Nephrology concluded that the patient s hypertension was caused in part by anxiety and intermittent obstruction of the renal pelvis and proximal collecting system secondary to mass effect from the multicystic mass. The patient subsequently underwent partial right nephrectomy to relieve the intermittent compression. Intraoperative records report an uneventful surgery. A clear demarcating line between the cystic lower pole and the normal-appearing upper pole was noted. DISCUSSION Localized cystic disease of the kidney is a rare condition, to our knowledge first described in 1964 by Bergman and Nehme. 1 This condition also has been referred to as unilateral cystic disease of the kidney, multiple unilateral renal cysts, segmental cystic disease of the kidney, and unilateral polycystic kidney disease. This latter term has been discouraged because it lends itself to confusion with the heritable form of autosomal dominant polycystic kidney disease (ADPKD). Localized cystic disease of the kidney is nonfamilial, nonprogressive, not associated with cysts or malformations in other organs, and not related to other genetic cystic diseases. The major defining feature is the presence of multiple benign simple cysts localized to a kidney or part of one, with otherwise normal renal parenchyma. The quoted number of reported cases in the literature ranges from 6 to just over 50. 1,2 The largest reported group (Slywotzky and Bosniak 3 )described clinical and imaging findings in 18 patients. Median age at detection was 54 years (range, years). This condition has rarely been described in the pediatric population, occurring in 1 child as young as 10 months. 4 There is a male predilection. The condition is benign and usually incidental. Symptoms, when present, include flank pain, hematuria, hypertension, and a palpable mass There is limited long-term follow up, but most patients show no progression of cystic disease and no deterioration in kidney function. The

3 Localized Cystic Disease of Kidney 611 Figure 2. T2-weighted (A) axial and (C) coronal and T1- weighted postgadolinium (B) axial and (D) coronal images confirm the ultrasound findings of multiple cystic lesions involving only the lower pole of the right kidney. T1 and T2 images are obtained at different levels through the kidney. pathogenesis is not known; however, at least 1 group has postulated that it may be secondary to a localized somatic defect in the PKD1 gene. The germ cells are not affected and therefore the defect is not heritable. 7 This theory would explain why there is a segmental collection of simple cysts with otherwise relatively normal kidney parenchyma and no cysts in other organs. It is not rare for a patient to have undergone complete or partial nephrectomy under the suspicion of malignancy. Figure 3. Pathology slide with hematoxylin and eosin stain shows benign multilocular cysts with adjacent and entrapped kidney parenchyma consisting of glomeruli and tubules (arrows). Localized cystic disease of the kidney has a characteristic appearance. It is possible to differentiate this entity based on imaging findings, thus avoiding unnecessary biopsy or surgical excision. The most common modality used in the evaluation of this localized cystic disease has been computed tomography, and the disease has characteristic findings: multiple simple cysts in a conglomerate mass with normal or atrophic intervening kidney parenchyma The cystic conglomerate may involve an entire kidney or a single segment. These cysts rarely contain thin-rim calcifications. 3 A few reports have described hyperdense cysts, believed secondary to hemorrhage, generally from trauma. 3 Two other important differentiating features are lack of cyst enhancement with contrast and lack of encapsulation. By definition, the contralateral kidney is normal, but may contain a few simple cysts. The condition is not associated with calculi. One of the earliest case reports by Cho et al 11 described the angiographic appearance: vessels stretched around an avascular mass, no neovascularity, and otherwise normal renal vessels. Ultrasonography often is performed as a preliminary imaging tool. Sonographic findings are typical, although nonspecific, and include a multiseptated complex mass with a normal contralateral

4 612 kidney. These findings are nondiagnostic and warrant additional workup. 3-5,9 To our knowledge, the literature reports MRI findings for only 2 patients. 3,12 MRI findings mirror computed tomography, including a conglomerate of localized simple cysts with normal intervening kidney parenchyma. There is no enhancing soft-tissue mass or papillary component. The cysts show no enhancement on postgadolinium images. Magnetic resonance angiography shows splaying of normal vessels around an avascular mass. MRI may aid in the diagnosis secondary to its multiplanar capabilities or be useful in follow-up because of the lack of ionizing radiation. The pathologic findings have been described. 2,3,5,7,9 Gross specimens show a nonencapsulated multicystic abnormality, with no solid or papillary component. Microscopic findings include cysts that are lined by simple cuboidal epithelium, with no papillary areas. In this regard, the cysts are indistinguishable from those seen in ADPKD. The defining feature is the presence of normal or compressed kidney parenchyma between cysts. There should be no mesenchymal tissue, metaplasia, blastema, or immature elements. The differential diagnosis of cystic disease in the kidney is broad, including benign and malignant processes. Localized cystic disease of the kidney is confused most frequently with ADPKD. ADPKD is characterized by bilateral involvement, although there have been pediatric cases reported to have an initial asymmetric presentation. 13 Patients with ADPKD have associated malformations, including liver and pancreatic cysts and intracranial aneurysms. 6 Other important differentiating features are a family history of kidney cysts and progressive impairment in kidney function. Acquired cystic disease and systemic conditions associated with kidney cysts (ie, tuberous sclerosis and von Hippel-Lindau disease) can be excluded from the differential based on appropriate clinical history, bilaterality, and associated systemic manifestations of these entities. Multicystic dysplastic kidney is the most common cystic disease of the kidney, often diagnosed on prenatal ultrasound. Multicystic dysplastic kidney should not be confused with localized cystic disease of the kidney, although it can present in 1 renal segment. When this occurs, the condition Dowden, Osunkoya, and Baumgarten usually affects the upper pole moiety of a duplex kidney and is accompanied by an obstructed or atretic upper pole ureter. 6,8 Cystic neoplasms that can be confused with localized cystic disease of the kidney include multilocular cystic nephroma, cystic renal cell carcinoma, and cystic Wilms tumor. These entities usually displace adjacent kidney parenchyma and never have normal kidney parenchyma interspersed between the cystic lesions. 3,5,6,12 Localized cystic disease of the kidney is not encapsulated and has no solid or papillary irregularity. The mentioned cystic neoplasms are encapsulated, and this feature is very helpful in distinguishing these lesions from localized cystic disease of the kidney. Despite these differing features, patients with this condition often undergo complete or partial nephrectomy secondary to the suspicion of malignancy. Localized cystic disease of the kidney is nonprogressive. Although a few patients have shown a slight increase in cyst size on follow-up, 3 most show no change in the size of cystic lesions. It also is not associated with the progressive decrease in kidney function seen with ADPKD. Surgical excision is not indicated unless the lesion results in significant symptoms, such as in our patient. It is important to differentiate localized cystic disease of the kidney from ADPKD. Although these 2 entities share similar features on microscopic evaluation, this differentiation can be accomplished by excluding contralateral kidney disease, genetic testing, and evaluation of family members for the presence of cystic kidney disease. Patients with localized cystic disease of the kidney should not be labeled as having unilateral ADPKD because this has both genetic and insurance implications. Although benign, follow-up imaging occasionally may be indicated, particularly in a young patient with questionable asymmetric onset of ADPKD or a patient with continued symptoms. MRI may have an important role in such cases because it does not use ionizing radiation. Localized cystic disease of the kidney has characteristic findings on imaging studies that, if known, can allow its differentiation from cystic neoplasms. Knowledge of this disease and its features may allow the avoidance of unnecessary kidney biopsy or surgical excision.

5 Localized Cystic Disease of Kidney 613 ACKNOWLEDGEMENTS Support: None. Financial Disclosure: None. REFERENCES 1. Bergman H, Nehme DA. Unilateral polycystic renal disease. NY State J Med. 1964;64: Bisceglia M, Galliani CA, Senger C, et al. Renal cystic diseases: a review. Adv Anat Pathol. 2006;13(1): Slywotzky C, Bosniak M. Localized cystic disease of the kidney. AJR Am J Roentgenol. 2001;176(4): Dugougeat F, Navarro O, Soares Souza AS, et al. Multiple unilateral renal cysts in two children. Pediatr Radiol. 2000;30(5): Casas J, Mariscal A, Pérez-Andrés R. Localized renal cystic disease: imaging findings, pathologic correlation, and management approach. Comput Med Imaging Graphics. 2002;26(4): Glassberg K. Renal dysplasia and cystic disease of the kidney. In: Wein A, ed. Campbell-Walsh Urology. 9th ed. Philadelphia, PA: Saunders Elsevier; 2007; Gouldesbrough DR, Fleming S. Unilateral and segmental localised polycystic kidney disease. J Clin Pathol. 1998; 51(9): Kim DJ, Kim MJ. Localized cystic disease of the kidney: CT findings. Abdom Imaging. 2003;28(4): Wankhar B, Batchala PP, Sailo S. Segmental cystic renal disease: sonographic and CT findings. J Clin Ultrasound. 2009;37(2): Hartman DS, Choyke PL, Hartman MS. From the RSNA refresher courses: a practical approach to the cystic renal mass. Radiographics. 2004;24(suppl 1):S Cho KJ, Thornbury JR, Bernstein J, Heidelberger KP, Walter JF. Localized cystic disease of the kidney: angiographic pathologic correlation. AJR Am J Roentgenol. 1979;132: Israel GM, Bosniak MA. MR imaging of cystic renal masses. Magn Reson Imaging Clin North Am. 2004;12(3): Porch P, Noe HN, Stapleton FB. Unilateral presentation of adult-type polycystic kidney disease in children. J Urol. 1986;135(4):