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Simple cyst of the kidney
Simple Cyst of the Kidney Joshua A. Becker, M.D., and Morton Schneider, M.D.
T
HE SIMPLE CYST OF THE KIDNEY is a benign mass lesion of the renal parenchyma. Its diagnostic importance in radiology and ultrasound is its differentiation from carcinoma of the kidney.
Classification Simple cysts are generally classified by their location. The great majority arise in the cortex while others originate in the medulla and the parapelvic or hilar area. Cysts may be multilocular, with septa separating the lumen of the cyst into multiple communicating or noncommunicating compartments. Simple cysts can also be multiple, but this form is completely different in nearly all respects from multicystic and polycystic disease.”
Etiology The cause of simple cyst of the kidney is unknown. Hepler’s hypothesis is that it is a retention cyst secondary to an obstructed tubule or tubular system, as a result of focal inflammation and vascular occlusion.“’ 1g,37 A second consideration is that it is a calyceal diverticulum (pyelogenic cyst) that has lost its connection to the collecting system. Pathologic examinations have given little aid to the elucidation of the origin of these cysts since the lining of flat endothelium is compatible with many theories of origin.18935’41 Exempted from this are a group of parapelvic cysts that have a transitional cell lining and may well be a duplication anomaly or a diverticulum. In disfavor today is the lymphatic origin of parapelvic cysts.
Incidence Most reports of the autopsy incidence of renal cysts stem from one article listing it as 3%-5%. ’ With high quality urography, the clinical rate in our experience is l%-2% of urograms. The sex distribution is equa1.6912There is no logical explanation for the observation that the lower pole is the
Joshua A. Becker, M.D.: Professor; Morton Schneider, M.D.: Instructor; State University of New York, Downstate Medical Center, 450 Clarkson Ave., Brooklyn, N. Y. 11203. 0 I9 75 by Grune & Stratton, Inc. Seminars
in Roentgenology,
Vol. X, No. 2 (April),
1975
most common site.4 The age incidence reveals that cysts are rare prior to age 30 but steadily increase in frequency thereafter. This further confirms the acquired nature of simple cyst. A cyst is so uncommon below age 30, that exploration of all young patients with a mass lesion may be indicated, irrespective of the diagnostic studies. Coexistence of a neoplasm and cyst in the same lesion is rare. In the Mayo Clinic experience, an incidence of less than 1% was noted.i3 Lang reported a 2% incidence.” Coexistence of cyst and tumor in the same kidney is not as rare. If a kidney has two masses,each must be evaluated individually. There is no assurance that if one mass is a cyst, the other will also be a cyst. CLINICAL
FINDINGS
Occasionally a patient will have symptoms of flank discomfort or pain, referable to the stretching of the renal capsule. In rare instances, hematuria, polycythemia,” or hypertension’ have been noted. Even jaundice from the compression of the common duct by a large right renal cyst has been reported.6 Thus, the simple cyst of the kidney is basically a benign lesion whose diagnosis is pursued only for its differentiation from a solid mass of the kidney. ROENTGEN
FINDINGS
Abdomen Film Films of the abdomen are of little aid in the diagnosis of a simple cyst of the kidney other than the demonstration of a mass effect in the renal area. An eggshell type of calcification about the periphery of the mass is noted in approximately 3% of renal cysts1g,2’932 and may well represent the residue of past inflammatory or hemorrhagic episodes (Fig. 1). “Eggshell” calcification is suggestive of simple cyst, but any type of calcification in a renal mass favors neoplasm. Thus, calcification should be highly suspect irrespective of its character.
Urography The main value of urography is the identification and confirmation of a renal mass and not the determination of its pathologic identity. The increase 103
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Fig. 1. Calcified simple cyst. “Eggshell” calcification is suggestive of simple cyst, but malignancy cannot be excluded, irrespective of the type of calcification.
in quality of urography over the past years has turned up many more renal massesthan were seen before. The quality is dependent upon the discipline of the radiologist doing the intravenous urogram. At the present time, contrast material in doses of 17 to 36 g of iodine are the average, administered in the form of 60-150 cc of a 50%60% solution. The use of either a lo-set film for the initial nephrogram or routine tomography aids greatly in the visualization of the renal parenchyma (Fig. 2). Since the demonstration of the renal outline is so essential, any urographic examination that does not do this is incomplete. This is most important in the identification of renal cysts, since the great majority of them are cortical in origin and they may even be pedunculated from the kidney with no distortion or displacement of the pelvicalyceal system. Intravenous urography may be helpful in separating a renal from an extrarenal mass but the distinction may be tenuous because of the abovementioned variable attachment of a renal cyst to the kidney. Even with high dose urography, not to be confused with nephrotomography, urographic examination is limited in its most finite aspect to confirmation of a renal origin of the mass. No interpretation of the nature of a renal
mass, whether simple cyst or other pathologic process, can be made from urography. Nephrotomography Nephrotomography is a very valuable procedure when appropriately performed. Nephrotomography is not simply obtaining tomograms during urography. To perform the study properly, approximately 70 g of iodine should be administered intravenously over a time interval no longer than 10 min, in the form of 150 cc of Hypaque 90, 270 cc of Conray 60, or 195 cc of Renografin 76. Never go over 75 Kvp and always utilize a reliable tomographic system with an arc of 20” to 50”. Tomographic sections should be obtained starting approximately 2 min after the beginning of the drip, in the appropriate AR, oblique, and lateral projections as needed. This approach is easier and as reliable as the bolus technique (rapid injection of undiluted contrast medium), and we feel has supplanted it in most radiologic practices. The proper nephrotomogram often demonstrates the sine qua non of the simple cyst: a thin wall, as if drawn by a pencil (Fig. 3).3 The wall visualization is dependent upon a total body effect and not on the excretory function of the kidney. It will last 15-20 min in the technique described above.
Fig. 2. The value of nephrotomography. right kidney. (B) On tomographic section
(Al During standard urography there is a suggestion of a possible an obvious mass on the anterior surface of the kidney is seen.
mass in the
Fig. 3. Nephrotomogram in simple cyst. (A) The urogram shows a mass effect at the lower pole of the right kidney. (B) The nephrotomographic section demonstrates the classical finding: a thin wall. This is entirely dependent on the total body opacification phenomenon. A beak and sharp demarcation are also identified and are compatible but not diagnostic of a cyst.
106
Nephrotomography is unsatisfactory in patients with renal failure. Therefore, it is not recommended when the creatinine is above 3 mg/ 100 ml. Additional nephrotomographic findings of a cyst, compatible but not diagnostic, are: (1) radiolucency of the mass, (2) sharp demarcation of the mass from the renal parenchyma, and (3) undermining of adjacent renal substance to produce a “claw” or “beak.“26 These findings cannot stand alone, since they merely represent an encapsulated mass that is growing slowly. Thus, tumor and cyst can simulate each other in these aspects (Fig. 4). Collateral retroperitoneal veins, noted in tumors, have not been seen with simple cyst, so their demonstration excludes a cyst. Cysts that are entirely intrarenal and some that are parapelvic are not amenable to a nephrotomographic interpretation, since the wall cannot be projected tangentially. There is no diagnostic technique to demonstrate their wall (Fig. 5). It has been our experience that nephrotomography is capable of demonstrating the peripheral wall of a pedunculated cyst in approximately half the patients. This correlates well with the review by King.” Therefore, although nephrotomography
BECKER
AND
SCHNEIDER
has a 95%97% accuracy rate, it is diagnostic only when the peripheral wall can be demonstrated in tomographic section.
Angiogaphy Angiography is a highly diagnostic procedure when performed in a selective modality.7~20~26 In no instance should a midaortic injection study be used as a basis of interpretation of a renal mass. In a simple cyst, the selective angiogram demonstrates the classical avascular appearance. The capillary nephrographic phase is nearly identical to that of nephrotomography (Fig. 6). The peripheral wall is less frequently seen than with nephrotomography because of the smaller total dose of contrast medium used in angiography. Unfortunately, some solid masses of the kidney also present an avascular appearance.* Those lesions that most commonly simulate a simple cyst are necrotic clear cell carcinoma and papiilary adenocarcinoma of renal tubular origin. In an attempt to differentiate these lesions from a simple cyst, vasopressor pharmacologic agents such as epinephrine, norepinephrine and angiotensin have been used. With this method, a neoplasm
Fig. 4. Nephrotomogram in cystic carcinoma of the kidney. (A) Tomography during the urographic examination demonstrate the wall of the mass. (6) At nephrotomography, a thick wall is seen, its opacification dependent upon of contrast. This case illustrates the crayon image of a wall, whereas in cyst (Fig. 3) the wall is pencil-line thin.
fails to the dose
SIMPLE
CYST OF THE
107
KIDNEY
should demonstrate some degree of neovascularity, while a cyst will not. We believe that every apparent cyst of the kidney examined angiographically should have a concurrent vasopressor study. Ultrasound
F:ig. 5. lntrarenal cyst. The mass was well appreciated on the urogram and on this nephrotomogram. There is no wa y of differentiating it from a solid tumor because the and the wall thickness w .iphery cannot be demonstrated, car mot be determined.
The most valuable diagnostic procedure in the evaluation of a mass of the kidney is ultrasound.15~‘6P29Y34This is done either in A Mode recording or preferably with B Mode compound scanning (Fig. 7). Ultrasound offers the unique opportunity to differentiate fluid containing structures from most solid soft tissue lesions. This procedure, unlike nephrotomography, almost always produces a diagnostic study and is noninvasive, an advantage over angiography. Recognition of a sonographically echoless cyst is made only with a high level of skill and a disciplined approach. As with all diagnostic procedures, amateurism favors error. A proper study requires a trained examiner and takes approximately 45 min, with 20 sonographic records of the kidney. The classical findings seen in A Mode are a totally echoless area at normal recording sensitivity and no evidence of echoes at low attenuation (high sensitivity). A Mode recording has the disadvan-
in renal cyst. Same patient as in Fig. 3. IA) Arterial phase demonstrates an avascular Fig. 6. The selactive arteriogram mass. (B) Nephrographic phase shows an appearance similar to Fig. 38. Note that the cyst wall is not seen. An insufficient quantity of contrast material has been injected to cause total body opacification.
108
BECKER
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Fig. 7. Renal cyst demonstrated by ultrasound scan. (A) The classical findings at normal scanning sensitivity are shown both in “A” Mode and (B) in “B” Mode. When the sensitivity is increased in (Cl “A” Mode and IDI “B” Mode, the mass still remained echoless, demonstrating its fluid content.
tage of lacking the usual imaging that a radiologist is accustomed to. B Mode scanning produces tomographic cross-sectional anatomy and is easier to handle. In B Mode scanning, the mass is (1) echoless at all levels of recording, (2) the posterior wall is sharply demarcated, and (3) at normal scanning sensitivity, the cystic area represents a sonolucent window, so that sonographic resolution is obtained distal to the mass. Correlation of the sonogram with the roentgen studies is extremely important. If the sonographic findings do not match the size or position of the mass in the roentgen study, the consideration of two lesions, cyst and other mass, should be suspected. The accuracy rate of sonography falls into the realm of over 95%. Some malignancies are cystic and certain rare solid massessimulate transsonic cysts, accounting for the occasional errors.
CJvstAspiration Cyst aspiration represents another highly diagThere nostic procedure. 8,10,14,23,24,25,30,31,39,42 are two current approaches for cyst aspiration. (1) The urogram is utilized to localize the kidney lesion, and then under fluoroscopic guidance to puncture the mass percutaneously. This has proven its diagnostic worth over the years. (2) The newer approach is to use ultrasound localization of the mass and to approach the mass percutaneously after the presumptive diagnosis of a cyst. Localization is preferably done with the B Modes. In almost all techniques, the patient is placed
in prone position and a posterior flank approach used. Cysts that are anterior to the kidney, especially in the parapelvic area, are somewhat hazardous to puncture since a transrenal needle path is required. To obviate this, a tangential approach to the anterior mass can be utilized. In addition, the exact course of the needle is determined by the scanning beam. Utilizing the scale of the storage oscilloscope, the exact depth of the cyst is known and the needle approach is thereby easily determined. Experienced examiners, accustomed to the technique of their discipline, have percutaneously aspirated masses as small as 2.5 cm in diameter. By measuring the cyst size, its volume can be determined. Aspiration of an inappropriate amount of fluid raises the suspicion that the mass is not entirely fluid and may have a solid component. Table 1 lists the average biochemical determinations of the aspirate. A major indicator of a complicating process is that of lactic acid dehydrogenase (LDH); its level in a simple cyst is considerably lower than that of blood. If a cyst level is higher, then the mass should not be presumed to be a cyst and further investigated. Lang has also called attention to the presence of fat within the fluid as an indicator of malignant potentiality of the lesion. He has also been able to predict the recurrence of the cyst by determining the cyst/blood sugar ratio. It is his feeling that if this ratio is 1 or greater, then the cyst will recur. If the ratio is less than 1, then the cyst, once de-
SIMPLE
CYST
OF
THE
109
KIDNEY Table
GernertL4
LanQ26
26 2.2
28 1.9
Not elevated
2.8 148 4.2 112
146 4.4 113
Clarke’ Urea (mg/lOO ml) Protein (g/100 ml) A/G Na (mEq/L) IC (mEq/L) CL (mEq/L) LDH (Int Units) Fat Glucose (mg/lOO
1
ml)
PH SPG Creatinine Color Cytology
compressed, will not recur.*s In our limited experience, this has not proven to be of value. Cytology and cell block may also reveal the malignant nature of a cyst. The fluid itself should be clear, varying in shade from straw color to deep amber; it should never be turbid or bloody. Although an occasional traumatic tap will produce a bloody aspirate, anything other than clear fluid should warrant further investigation. Single, double or triple contrast studies of the cyst have been reported (Fig. 8). Utilizing gas as a negative shadow, water soluble contrast agents as an intermediary shadow, and oily contrast material as a more dense shadow, the wall and its in-
Leopold”
Low Low
0.30
Clear Negative
Amber
120 7.7 1.015 0.9
ternal contour have been demonstrated. The purpose here is to identify a mass protruding into the cyst lumen, and thereby exclude the remote possibility of coexistence of a tumor and cyst. For this procedure to be disciplined, films in all projections, even sometimes inverted films, must be obtained so that all the walls of the cyst can be shown. In the hands of those using this technique, this has been extremely worthwhile. However, it has been our impression that this is extremely time consuming and does represent a major invasive diagnostic procedure. An oily contrast medium, such as Pantopaque, may produce a systemic febrile reaction. Pantopaque has caused severe localized inflammatory reaction and fibrosis, making surgery difficult. Oily contrast material has been used in an attempt to prevent the recurrence of the cyst.40 There are equivocal statistics in this regard and, therefore, it is our feeling that oily materials should not be used. There have been no complications recorded from gas or water soluble contrast agents in double contrast studies. PHI LOSOPHY
Fig. 8. Contrast study of simple cyst. The injected renal mass shows water-soluble contrast material mixing with the cyst fluid and gas in the upper portion of the cyst. This is a typical appearance in the upright projection.
A continuing discourse appears within the literature between the surgical and radiologic approach to the apparent simple cyst of the kidney. Some surgeons feel that every renal mass must be explored. This is as fallacious as some radiologists’ view that no apparent cyst should be explored. The patient’s welfare and clinical status are the major deciding factors to the approach to both diagnosis and treatment. No experienced physician would proceed with surgery on an elderly patient having severe myocardial disease, or uncontrolled diabetes mellitus and a sonographic and cyst aspiration
110
BECKER
diagnosis of a cyst to exclude a tumor.33 On the contrary, in a patient with a cancer phobia and an apparent simple cyst of the kidney demonstrated by similar means, an appropriate approach might be surgical exploration. The great worry of the urologist in the percutaneous approach to a mass is the danger of seeding of the needle track, if the mass does in truth turn out to be a malignant process. However, if a tumor is unexpectedly found by the percutaneous aspiration, the earlier diagnosis may actually give the patient a better prognosis.36S38 In conclusion, we feel a secure diagnosis of renal cyst should rest upon at least two studies confirmatory of cyst, sonography along with either renal cyst aspiration or nephrotomography. We have not included cyst injection because of our limited experience. This may well prove to be an excellent confirmatory method. We have purposely placed angiography last because after years of experience, we have encountered a number of tumors that are totally avascular, even with magnification angiography and pharmacological agents. Our present feeling is that angiography is indicated in all cases prior to surgery to plan the surgical approach, but not for diagnosis. Once the initial diagnostic studies are indicative of a solid mass or equivocal for cyst, the lesion becomes surgical. A certain number of cysts will be explored or some neoplasms will be missed. We have excluded the use of radioisotopes because we feel they have a limited role in cyst-tumor differentiation. REFERENCES 1. Babka JC, Cohen MS, Sode J: Solitary intrarenal cyst causing hypertension. N Engl J Med 291:343-344, 1974 2. Becker JA, Fleming R, Kanter I, et al: Misleading appearances in renal angiography. Radiology 88:691-700, 1967 3. Bosniak M, Faegenburg D: The thick-wall sign: An important finding in nephrotomography. Radiology 84: 692-698, 1965 4. Braasch WF, Hendrick JA: Renal cysts, simple and otherwise. J Urol Sl:l-10, 1944 5. Branch CF: Some observations of solitary cyst of the kidney. J Urol21:451-453, 1929 6. Campbell MF, Harrison JH: Urology (ed 3). Philadelphia, WB Saunders, 1970 7. Campbell DR, Mason WF, Manchester JD: Arteriography in renal mass lesions. J Can Assoc Radio1 24:309320,1973 8. Clarke BG, Hurwitz IS, Dubinsky E: Solitary serous cysts of the kidney. Biochemical, cytological, and histologic studies. J Urol 75:772-775, 1956
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9. Daniel WW Jr, Hartman GW, Witten DM, et al: Calcified renal masses: A review of ten years experience at the Mayo Clinic. Radiology 103:503-508, 1972 10. De Weerd JH: Percutaneous aspiration of selected expanding renal lesions. J Urol 87:303-308, 1962 11. Elkin M, Bernstein J: Cystic disease of the kidney. Radiological and pathological considerations. Clin Radio1 20:65-82, 1969 12. Emmett JL, Witten DM: Clinical Urography (ed 3). Philadelphia, WB Saunders, 197 1 13. Emmett JL, Levine SR, Woolner LB: Co-existence of renal cyst and tumor: Incidence in 1007 cases. Br J Urol35:403-410, 1963 14. Gernert JE, Stein J, Bischoff AJ: Solitary renal cysts and experience with 100 cases. J Urol 100:251253, 1968 15. Goldberg BB, Pollack HM: Differentiation of renal masses using A Mode ultrasound. J Urol 105:765-771, 1971 16. Goldberg BB, Pollack HM: Ultrasonically guided renal cyst aspiration. J Ural 109:5-7, 1973 17. Goodman T, Grice HC, Becking GC, et al: A cystic nephropathy induced by nordihydroguaiaretic acid in the rat. Light and electron microscope investigation. Lab Invest 23:93-107, 1970 18. Heggo 0: A microdissection study of cystic disease of the kidneys in adults. J Path01 Bacterial 91:311-315, 1966 19. Hepler AB: Experimental production of cyst of the kidney by fulguration of papilla of rabbits one lobed kidney and ligating posterior branch of renal artery. J Urol 44:206, 1946 20. Kahn PC, Wise HM Jr: The use of epinephrine in selective angiography of renal masses.J Uro199: 133-l 38, 1968 21. Kikkawa K, Lasser E: “Ring-like” or “Rim-like” calcification in renal cell carcinoma. Am J Roentgen01 107:737-742, 1969 22. King DL: Renal ultrasonography: An aid in the clinical evaluation of renal mass. Radiology 105:633-640, 1972 23 Kristensen JK, Holm HH, Rasmussen SN, et al: Ultrasonically guided percutaneous puncture of renal masses. Stand J Urol Nephrol6 (Suppl 15):49-56, 1972 24. Lalli AF: Percutaneous aspiration of renal masses. Am J Roentgen01 101:700-704, 1967 25. Lang EK: The differential diagnosis of renal cysts and tumors: Cyst puncture, aspiration and analysis of cyst content for fat as diagnostic criteria for renal cysts. Radiology 87:883-888, 1966 26. Lang EK: Roentgenographic assessmentof asymptomatic renal lesions. Radiology 109:257-269, 1973 27. Lang EK: Coexistence of cyst and tumor in the same kidney. Radiology 101:7-16, 1971 28. Lang EK: Personal communication. 29. Leopold GR, Talner LB, Asher W, et al: Renal ultrasonography: An updated approach to the diagnosis of renal cyst. Radiology 109:671-678, 1973 30. Lindblom K: Diagnostic kidney puncture in cysts and tumors. Am J Roentgen01 68:209-215, 1952 31. Lindblom K: Percutaneous puncture of renal cysts and tumors. Acta Radio1 27~66-72, 1946
SIMPLE
CYST OF THE
KIDNEY
32. Phillips TL, Chin FG, Palubinskas AJ: Calcification in renal masses.An 11 year survey. Radiology 80:786-94, 1963 33. Plaine LI, Hinmann FJ: Malignancy in asymptomatic renal masses.J Urol94:342-347, 1965 34. Pollack HM, Goldberg B, Bogash M: Changing concepts in the diagnosis and management of renal cysts. J Urol 111:326-329, 1974 35. Robbins S: Pathologic basis of disease.Philadelphia, WB Saunders, 1974 36. Robson CJ: Radical nephrectomy for renal cell carcinoma. J Urol 89: 37-42, 1963 37. Safoud M, Cracker J, Vesnier R: Experimental cystic disease of the kidney: Sequential, functional and morphological studies. Lab Invest 23:392400, 1970 38. Von Schreeb T, Arner 0, Skousted G, et al: Renal
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adenocarcinoma: Is there a risk of spreading tumor cells in diagnostic puncture? Stand J Urol Nephrol 1: 270-276, 1967 39. Thornbury JR: Needle aspiration of avascular renal lesions: Correlation of contrast medium injection with cytologic and arteriographic diagnosis. Radiology 105: 299-302, 1972 40. Vestby GW: Percutaneous puncture of renal cysts: New method in therapeutic management. Invest Radio1 2:449-462,1967 41. Wahlqvist L: Cystic disorders of the kidney: Review of pathogenesis and classification. J Urol 97:1-6, 1967 42. Witherington R, Rinke JR: Percutaneous needle puncture in the diagnosis of renal cysts. J Urol 95:733737, 1966
T
HE SIMPLE CYST OF THE KIDNEY is a benign mass lesion of the renal parenchyma. Its diagnostic importance in radiology and ultrasound is its differentiation from carcinoma of the kidney.
Classification Simple cysts are generally classified by their location. The great majority arise in the cortex while others originate in the medulla and the parapelvic or hilar area. Cysts may be multilocular, with septa separating the lumen of the cyst into multiple communicating or noncommunicating compartments. Simple cysts can also be multiple, but this form is completely different in nearly all respects from multicystic and polycystic disease.”
Etiology The cause of simple cyst of the kidney is unknown. Hepler’s hypothesis is that it is a retention cyst secondary to an obstructed tubule or tubular system, as a result of focal inflammation and vascular occlusion.“’ 1g,37 A second consideration is that it is a calyceal diverticulum (pyelogenic cyst) that has lost its connection to the collecting system. Pathologic examinations have given little aid to the elucidation of the origin of these cysts since the lining of flat endothelium is compatible with many theories of origin.18935’41 Exempted from this are a group of parapelvic cysts that have a transitional cell lining and may well be a duplication anomaly or a diverticulum. In disfavor today is the lymphatic origin of parapelvic cysts.
Incidence Most reports of the autopsy incidence of renal cysts stem from one article listing it as 3%-5%. ’ With high quality urography, the clinical rate in our experience is l%-2% of urograms. The sex distribution is equa1.6912There is no logical explanation for the observation that the lower pole is the
Joshua A. Becker, M.D.: Professor; Morton Schneider, M.D.: Instructor; State University of New York, Downstate Medical Center, 450 Clarkson Ave., Brooklyn, N. Y. 11203. 0 I9 75 by Grune & Stratton, Inc. Seminars
in Roentgenology,
Vol. X, No. 2 (April),
1975
most common site.4 The age incidence reveals that cysts are rare prior to age 30 but steadily increase in frequency thereafter. This further confirms the acquired nature of simple cyst. A cyst is so uncommon below age 30, that exploration of all young patients with a mass lesion may be indicated, irrespective of the diagnostic studies. Coexistence of a neoplasm and cyst in the same lesion is rare. In the Mayo Clinic experience, an incidence of less than 1% was noted.i3 Lang reported a 2% incidence.” Coexistence of cyst and tumor in the same kidney is not as rare. If a kidney has two masses,each must be evaluated individually. There is no assurance that if one mass is a cyst, the other will also be a cyst. CLINICAL
FINDINGS
Occasionally a patient will have symptoms of flank discomfort or pain, referable to the stretching of the renal capsule. In rare instances, hematuria, polycythemia,” or hypertension’ have been noted. Even jaundice from the compression of the common duct by a large right renal cyst has been reported.6 Thus, the simple cyst of the kidney is basically a benign lesion whose diagnosis is pursued only for its differentiation from a solid mass of the kidney. ROENTGEN
FINDINGS
Abdomen Film Films of the abdomen are of little aid in the diagnosis of a simple cyst of the kidney other than the demonstration of a mass effect in the renal area. An eggshell type of calcification about the periphery of the mass is noted in approximately 3% of renal cysts1g,2’932 and may well represent the residue of past inflammatory or hemorrhagic episodes (Fig. 1). “Eggshell” calcification is suggestive of simple cyst, but any type of calcification in a renal mass favors neoplasm. Thus, calcification should be highly suspect irrespective of its character.
Urography The main value of urography is the identification and confirmation of a renal mass and not the determination of its pathologic identity. The increase 103
BECKER
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SCHNEIDER
Fig. 1. Calcified simple cyst. “Eggshell” calcification is suggestive of simple cyst, but malignancy cannot be excluded, irrespective of the type of calcification.
in quality of urography over the past years has turned up many more renal massesthan were seen before. The quality is dependent upon the discipline of the radiologist doing the intravenous urogram. At the present time, contrast material in doses of 17 to 36 g of iodine are the average, administered in the form of 60-150 cc of a 50%60% solution. The use of either a lo-set film for the initial nephrogram or routine tomography aids greatly in the visualization of the renal parenchyma (Fig. 2). Since the demonstration of the renal outline is so essential, any urographic examination that does not do this is incomplete. This is most important in the identification of renal cysts, since the great majority of them are cortical in origin and they may even be pedunculated from the kidney with no distortion or displacement of the pelvicalyceal system. Intravenous urography may be helpful in separating a renal from an extrarenal mass but the distinction may be tenuous because of the abovementioned variable attachment of a renal cyst to the kidney. Even with high dose urography, not to be confused with nephrotomography, urographic examination is limited in its most finite aspect to confirmation of a renal origin of the mass. No interpretation of the nature of a renal
mass, whether simple cyst or other pathologic process, can be made from urography. Nephrotomography Nephrotomography is a very valuable procedure when appropriately performed. Nephrotomography is not simply obtaining tomograms during urography. To perform the study properly, approximately 70 g of iodine should be administered intravenously over a time interval no longer than 10 min, in the form of 150 cc of Hypaque 90, 270 cc of Conray 60, or 195 cc of Renografin 76. Never go over 75 Kvp and always utilize a reliable tomographic system with an arc of 20” to 50”. Tomographic sections should be obtained starting approximately 2 min after the beginning of the drip, in the appropriate AR, oblique, and lateral projections as needed. This approach is easier and as reliable as the bolus technique (rapid injection of undiluted contrast medium), and we feel has supplanted it in most radiologic practices. The proper nephrotomogram often demonstrates the sine qua non of the simple cyst: a thin wall, as if drawn by a pencil (Fig. 3).3 The wall visualization is dependent upon a total body effect and not on the excretory function of the kidney. It will last 15-20 min in the technique described above.
Fig. 2. The value of nephrotomography. right kidney. (B) On tomographic section
(Al During standard urography there is a suggestion of a possible an obvious mass on the anterior surface of the kidney is seen.
mass in the
Fig. 3. Nephrotomogram in simple cyst. (A) The urogram shows a mass effect at the lower pole of the right kidney. (B) The nephrotomographic section demonstrates the classical finding: a thin wall. This is entirely dependent on the total body opacification phenomenon. A beak and sharp demarcation are also identified and are compatible but not diagnostic of a cyst.
106
Nephrotomography is unsatisfactory in patients with renal failure. Therefore, it is not recommended when the creatinine is above 3 mg/ 100 ml. Additional nephrotomographic findings of a cyst, compatible but not diagnostic, are: (1) radiolucency of the mass, (2) sharp demarcation of the mass from the renal parenchyma, and (3) undermining of adjacent renal substance to produce a “claw” or “beak.“26 These findings cannot stand alone, since they merely represent an encapsulated mass that is growing slowly. Thus, tumor and cyst can simulate each other in these aspects (Fig. 4). Collateral retroperitoneal veins, noted in tumors, have not been seen with simple cyst, so their demonstration excludes a cyst. Cysts that are entirely intrarenal and some that are parapelvic are not amenable to a nephrotomographic interpretation, since the wall cannot be projected tangentially. There is no diagnostic technique to demonstrate their wall (Fig. 5). It has been our experience that nephrotomography is capable of demonstrating the peripheral wall of a pedunculated cyst in approximately half the patients. This correlates well with the review by King.” Therefore, although nephrotomography
BECKER
AND
SCHNEIDER
has a 95%97% accuracy rate, it is diagnostic only when the peripheral wall can be demonstrated in tomographic section.
Angiogaphy Angiography is a highly diagnostic procedure when performed in a selective modality.7~20~26 In no instance should a midaortic injection study be used as a basis of interpretation of a renal mass. In a simple cyst, the selective angiogram demonstrates the classical avascular appearance. The capillary nephrographic phase is nearly identical to that of nephrotomography (Fig. 6). The peripheral wall is less frequently seen than with nephrotomography because of the smaller total dose of contrast medium used in angiography. Unfortunately, some solid masses of the kidney also present an avascular appearance.* Those lesions that most commonly simulate a simple cyst are necrotic clear cell carcinoma and papiilary adenocarcinoma of renal tubular origin. In an attempt to differentiate these lesions from a simple cyst, vasopressor pharmacologic agents such as epinephrine, norepinephrine and angiotensin have been used. With this method, a neoplasm
Fig. 4. Nephrotomogram in cystic carcinoma of the kidney. (A) Tomography during the urographic examination demonstrate the wall of the mass. (6) At nephrotomography, a thick wall is seen, its opacification dependent upon of contrast. This case illustrates the crayon image of a wall, whereas in cyst (Fig. 3) the wall is pencil-line thin.
fails to the dose
SIMPLE
CYST OF THE
107
KIDNEY
should demonstrate some degree of neovascularity, while a cyst will not. We believe that every apparent cyst of the kidney examined angiographically should have a concurrent vasopressor study. Ultrasound
F:ig. 5. lntrarenal cyst. The mass was well appreciated on the urogram and on this nephrotomogram. There is no wa y of differentiating it from a solid tumor because the and the wall thickness w .iphery cannot be demonstrated, car mot be determined.
The most valuable diagnostic procedure in the evaluation of a mass of the kidney is ultrasound.15~‘6P29Y34This is done either in A Mode recording or preferably with B Mode compound scanning (Fig. 7). Ultrasound offers the unique opportunity to differentiate fluid containing structures from most solid soft tissue lesions. This procedure, unlike nephrotomography, almost always produces a diagnostic study and is noninvasive, an advantage over angiography. Recognition of a sonographically echoless cyst is made only with a high level of skill and a disciplined approach. As with all diagnostic procedures, amateurism favors error. A proper study requires a trained examiner and takes approximately 45 min, with 20 sonographic records of the kidney. The classical findings seen in A Mode are a totally echoless area at normal recording sensitivity and no evidence of echoes at low attenuation (high sensitivity). A Mode recording has the disadvan-
in renal cyst. Same patient as in Fig. 3. IA) Arterial phase demonstrates an avascular Fig. 6. The selactive arteriogram mass. (B) Nephrographic phase shows an appearance similar to Fig. 38. Note that the cyst wall is not seen. An insufficient quantity of contrast material has been injected to cause total body opacification.
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Fig. 7. Renal cyst demonstrated by ultrasound scan. (A) The classical findings at normal scanning sensitivity are shown both in “A” Mode and (B) in “B” Mode. When the sensitivity is increased in (Cl “A” Mode and IDI “B” Mode, the mass still remained echoless, demonstrating its fluid content.
tage of lacking the usual imaging that a radiologist is accustomed to. B Mode scanning produces tomographic cross-sectional anatomy and is easier to handle. In B Mode scanning, the mass is (1) echoless at all levels of recording, (2) the posterior wall is sharply demarcated, and (3) at normal scanning sensitivity, the cystic area represents a sonolucent window, so that sonographic resolution is obtained distal to the mass. Correlation of the sonogram with the roentgen studies is extremely important. If the sonographic findings do not match the size or position of the mass in the roentgen study, the consideration of two lesions, cyst and other mass, should be suspected. The accuracy rate of sonography falls into the realm of over 95%. Some malignancies are cystic and certain rare solid massessimulate transsonic cysts, accounting for the occasional errors.
CJvstAspiration Cyst aspiration represents another highly diagThere nostic procedure. 8,10,14,23,24,25,30,31,39,42 are two current approaches for cyst aspiration. (1) The urogram is utilized to localize the kidney lesion, and then under fluoroscopic guidance to puncture the mass percutaneously. This has proven its diagnostic worth over the years. (2) The newer approach is to use ultrasound localization of the mass and to approach the mass percutaneously after the presumptive diagnosis of a cyst. Localization is preferably done with the B Modes. In almost all techniques, the patient is placed
in prone position and a posterior flank approach used. Cysts that are anterior to the kidney, especially in the parapelvic area, are somewhat hazardous to puncture since a transrenal needle path is required. To obviate this, a tangential approach to the anterior mass can be utilized. In addition, the exact course of the needle is determined by the scanning beam. Utilizing the scale of the storage oscilloscope, the exact depth of the cyst is known and the needle approach is thereby easily determined. Experienced examiners, accustomed to the technique of their discipline, have percutaneously aspirated masses as small as 2.5 cm in diameter. By measuring the cyst size, its volume can be determined. Aspiration of an inappropriate amount of fluid raises the suspicion that the mass is not entirely fluid and may have a solid component. Table 1 lists the average biochemical determinations of the aspirate. A major indicator of a complicating process is that of lactic acid dehydrogenase (LDH); its level in a simple cyst is considerably lower than that of blood. If a cyst level is higher, then the mass should not be presumed to be a cyst and further investigated. Lang has also called attention to the presence of fat within the fluid as an indicator of malignant potentiality of the lesion. He has also been able to predict the recurrence of the cyst by determining the cyst/blood sugar ratio. It is his feeling that if this ratio is 1 or greater, then the cyst will recur. If the ratio is less than 1, then the cyst, once de-
SIMPLE
CYST
OF
THE
109
KIDNEY Table
GernertL4
LanQ26
26 2.2
28 1.9
Not elevated
2.8 148 4.2 112
146 4.4 113
Clarke’ Urea (mg/lOO ml) Protein (g/100 ml) A/G Na (mEq/L) IC (mEq/L) CL (mEq/L) LDH (Int Units) Fat Glucose (mg/lOO
1
ml)
PH SPG Creatinine Color Cytology
compressed, will not recur.*s In our limited experience, this has not proven to be of value. Cytology and cell block may also reveal the malignant nature of a cyst. The fluid itself should be clear, varying in shade from straw color to deep amber; it should never be turbid or bloody. Although an occasional traumatic tap will produce a bloody aspirate, anything other than clear fluid should warrant further investigation. Single, double or triple contrast studies of the cyst have been reported (Fig. 8). Utilizing gas as a negative shadow, water soluble contrast agents as an intermediary shadow, and oily contrast material as a more dense shadow, the wall and its in-
Leopold”
Low Low
0.30
Clear Negative
Amber
120 7.7 1.015 0.9
ternal contour have been demonstrated. The purpose here is to identify a mass protruding into the cyst lumen, and thereby exclude the remote possibility of coexistence of a tumor and cyst. For this procedure to be disciplined, films in all projections, even sometimes inverted films, must be obtained so that all the walls of the cyst can be shown. In the hands of those using this technique, this has been extremely worthwhile. However, it has been our impression that this is extremely time consuming and does represent a major invasive diagnostic procedure. An oily contrast medium, such as Pantopaque, may produce a systemic febrile reaction. Pantopaque has caused severe localized inflammatory reaction and fibrosis, making surgery difficult. Oily contrast material has been used in an attempt to prevent the recurrence of the cyst.40 There are equivocal statistics in this regard and, therefore, it is our feeling that oily materials should not be used. There have been no complications recorded from gas or water soluble contrast agents in double contrast studies. PHI LOSOPHY
Fig. 8. Contrast study of simple cyst. The injected renal mass shows water-soluble contrast material mixing with the cyst fluid and gas in the upper portion of the cyst. This is a typical appearance in the upright projection.
A continuing discourse appears within the literature between the surgical and radiologic approach to the apparent simple cyst of the kidney. Some surgeons feel that every renal mass must be explored. This is as fallacious as some radiologists’ view that no apparent cyst should be explored. The patient’s welfare and clinical status are the major deciding factors to the approach to both diagnosis and treatment. No experienced physician would proceed with surgery on an elderly patient having severe myocardial disease, or uncontrolled diabetes mellitus and a sonographic and cyst aspiration
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diagnosis of a cyst to exclude a tumor.33 On the contrary, in a patient with a cancer phobia and an apparent simple cyst of the kidney demonstrated by similar means, an appropriate approach might be surgical exploration. The great worry of the urologist in the percutaneous approach to a mass is the danger of seeding of the needle track, if the mass does in truth turn out to be a malignant process. However, if a tumor is unexpectedly found by the percutaneous aspiration, the earlier diagnosis may actually give the patient a better prognosis.36S38 In conclusion, we feel a secure diagnosis of renal cyst should rest upon at least two studies confirmatory of cyst, sonography along with either renal cyst aspiration or nephrotomography. We have not included cyst injection because of our limited experience. This may well prove to be an excellent confirmatory method. We have purposely placed angiography last because after years of experience, we have encountered a number of tumors that are totally avascular, even with magnification angiography and pharmacological agents. Our present feeling is that angiography is indicated in all cases prior to surgery to plan the surgical approach, but not for diagnosis. Once the initial diagnostic studies are indicative of a solid mass or equivocal for cyst, the lesion becomes surgical. A certain number of cysts will be explored or some neoplasms will be missed. We have excluded the use of radioisotopes because we feel they have a limited role in cyst-tumor differentiation. REFERENCES 1. Babka JC, Cohen MS, Sode J: Solitary intrarenal cyst causing hypertension. N Engl J Med 291:343-344, 1974 2. Becker JA, Fleming R, Kanter I, et al: Misleading appearances in renal angiography. Radiology 88:691-700, 1967 3. Bosniak M, Faegenburg D: The thick-wall sign: An important finding in nephrotomography. Radiology 84: 692-698, 1965 4. Braasch WF, Hendrick JA: Renal cysts, simple and otherwise. J Urol Sl:l-10, 1944 5. Branch CF: Some observations of solitary cyst of the kidney. J Urol21:451-453, 1929 6. Campbell MF, Harrison JH: Urology (ed 3). Philadelphia, WB Saunders, 1970 7. Campbell DR, Mason WF, Manchester JD: Arteriography in renal mass lesions. J Can Assoc Radio1 24:309320,1973 8. Clarke BG, Hurwitz IS, Dubinsky E: Solitary serous cysts of the kidney. Biochemical, cytological, and histologic studies. J Urol 75:772-775, 1956
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9. Daniel WW Jr, Hartman GW, Witten DM, et al: Calcified renal masses: A review of ten years experience at the Mayo Clinic. Radiology 103:503-508, 1972 10. De Weerd JH: Percutaneous aspiration of selected expanding renal lesions. J Urol 87:303-308, 1962 11. Elkin M, Bernstein J: Cystic disease of the kidney. Radiological and pathological considerations. Clin Radio1 20:65-82, 1969 12. Emmett JL, Witten DM: Clinical Urography (ed 3). Philadelphia, WB Saunders, 197 1 13. Emmett JL, Levine SR, Woolner LB: Co-existence of renal cyst and tumor: Incidence in 1007 cases. Br J Urol35:403-410, 1963 14. Gernert JE, Stein J, Bischoff AJ: Solitary renal cysts and experience with 100 cases. J Urol 100:251253, 1968 15. Goldberg BB, Pollack HM: Differentiation of renal masses using A Mode ultrasound. J Urol 105:765-771, 1971 16. Goldberg BB, Pollack HM: Ultrasonically guided renal cyst aspiration. J Ural 109:5-7, 1973 17. Goodman T, Grice HC, Becking GC, et al: A cystic nephropathy induced by nordihydroguaiaretic acid in the rat. Light and electron microscope investigation. Lab Invest 23:93-107, 1970 18. Heggo 0: A microdissection study of cystic disease of the kidneys in adults. J Path01 Bacterial 91:311-315, 1966 19. Hepler AB: Experimental production of cyst of the kidney by fulguration of papilla of rabbits one lobed kidney and ligating posterior branch of renal artery. J Urol 44:206, 1946 20. Kahn PC, Wise HM Jr: The use of epinephrine in selective angiography of renal masses.J Uro199: 133-l 38, 1968 21. Kikkawa K, Lasser E: “Ring-like” or “Rim-like” calcification in renal cell carcinoma. Am J Roentgen01 107:737-742, 1969 22. King DL: Renal ultrasonography: An aid in the clinical evaluation of renal mass. Radiology 105:633-640, 1972 23 Kristensen JK, Holm HH, Rasmussen SN, et al: Ultrasonically guided percutaneous puncture of renal masses. Stand J Urol Nephrol6 (Suppl 15):49-56, 1972 24. Lalli AF: Percutaneous aspiration of renal masses. Am J Roentgen01 101:700-704, 1967 25. Lang EK: The differential diagnosis of renal cysts and tumors: Cyst puncture, aspiration and analysis of cyst content for fat as diagnostic criteria for renal cysts. Radiology 87:883-888, 1966 26. Lang EK: Roentgenographic assessmentof asymptomatic renal lesions. Radiology 109:257-269, 1973 27. Lang EK: Coexistence of cyst and tumor in the same kidney. Radiology 101:7-16, 1971 28. Lang EK: Personal communication. 29. Leopold GR, Talner LB, Asher W, et al: Renal ultrasonography: An updated approach to the diagnosis of renal cyst. Radiology 109:671-678, 1973 30. Lindblom K: Diagnostic kidney puncture in cysts and tumors. Am J Roentgen01 68:209-215, 1952 31. Lindblom K: Percutaneous puncture of renal cysts and tumors. Acta Radio1 27~66-72, 1946
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32. Phillips TL, Chin FG, Palubinskas AJ: Calcification in renal masses.An 11 year survey. Radiology 80:786-94, 1963 33. Plaine LI, Hinmann FJ: Malignancy in asymptomatic renal masses.J Urol94:342-347, 1965 34. Pollack HM, Goldberg B, Bogash M: Changing concepts in the diagnosis and management of renal cysts. J Urol 111:326-329, 1974 35. Robbins S: Pathologic basis of disease.Philadelphia, WB Saunders, 1974 36. Robson CJ: Radical nephrectomy for renal cell carcinoma. J Urol 89: 37-42, 1963 37. Safoud M, Cracker J, Vesnier R: Experimental cystic disease of the kidney: Sequential, functional and morphological studies. Lab Invest 23:392400, 1970 38. Von Schreeb T, Arner 0, Skousted G, et al: Renal
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adenocarcinoma: Is there a risk of spreading tumor cells in diagnostic puncture? Stand J Urol Nephrol 1: 270-276, 1967 39. Thornbury JR: Needle aspiration of avascular renal lesions: Correlation of contrast medium injection with cytologic and arteriographic diagnosis. Radiology 105: 299-302, 1972 40. Vestby GW: Percutaneous puncture of renal cysts: New method in therapeutic management. Invest Radio1 2:449-462,1967 41. Wahlqvist L: Cystic disorders of the kidney: Review of pathogenesis and classification. J Urol 97:1-6, 1967 42. Witherington R, Rinke JR: Percutaneous needle puncture in the diagnosis of renal cysts. J Urol 95:733737, 1966