Miscellaneous Acquired Cystic Lesions of the Kidney and Retroperitoneum Richard M. Friedenberg,
M.D., and Ralph M. Lilienfeld,
A
CQUIRED CYSTIC LESIONS of the kidney are the product of several diseases of different etiology and are usually readily distinguished from the renal cysts discussed elsewhere in this Seminar. These acquired lesions are, in fact, cavities that have formed within or adjacent to the renal parenchyma, and they are variously lined by fibrous tissue, necrotic tumor, endothelium, or necrotic or intact epithelium, depending upon their cause and stage of evolution. These acquired lesions are best classified by etiology. (1) Cystic hematomas (a) traumatic (b) spontaneous (2) Inflammatory cysts (a) pyogenic (b) tuberculous (c) papillary necrosis (d) parasitic (3) Cystic neoplasms (4) Communicating cystic lesions (a) calyceal diverticulum (b) hydrocalyx (c) communicating cyst (5) Pararenal cysts (a) parapelvic (b) pararenal pseudocyst CYSTIC
HEMATOMAS
Renal hemorrhage may be traumatic or spontaneous in origin. Spontaneous hemorrhage occurs secondary to the administration of anticoagulants, a bleeding diathesis, vascular erosion by tumor, vasculitis from drug abuse, embolic infarction2’ and occasionally from undetermined cause. Depending upon the site and extent of bleeding, the accumulated blood may either seep into the renal tubules, breech the pelvicalyceal system (with resulting hematuria), or extravasate through the Richard M. Friedenberg, M.D.: Professor and Chairman, Department of Radiology, New York Medical CollegeMetropolitan Hospital Center, New York, N. Y. 10029; Ralph M. Lilienfeld, M.D.: Associate Professor, Department of Radiology, New York Medical College-Metropolitan Hospital Center, New York, N. Y. 10029. o 1975 by Grune & Stratton, Inc. Seminars
in Roentgenology,
Vol.
X, No. 2 (April),
1975
M.D.
lacerated capsule to form a perinephric hematoma. Blood contained within the renal parenchyma forms an intrarenal hematoma (Fig. 1); when confined between cortex and capsule it produces a subcapsular hematoma. The hematoma is lucent on nephrotomography and avascular on angiography. The distinguishing hallmark of the intrarenal hematoma is its rapid reversibility.18 In contrast to the simple cyst, the rapidly developing intrarenal hematoma, even when peripherally located, does not form the characteristic beak caused by the slow expansion of the simple cyst, which pulls out the marginal parenchyma. In the vascular phase of nephrotomography or angiography, the hematoma usually presents with a thick marginal rim, mimicking abscessmore than cyst. Calcification, which might be expected as a common feature of intrarenal hematoma, is in our experience unusual, it is more suggestive of tumor, cyst, or abscess. The subcapsular hematoma compresses the relatively unyielding renal parenchyma as it strips the capsule from the cortex. Thus, the convexity of the hematoma is directed away from the kidney with the maximum convexity at the geographic center of the hematoma. The underlying cortex becomes flat or slightly concave (Fig. 2). The capsule, supplied by twigs from the capsular artery is frequently visualized both on nephrotomography and angiography. The displaced capsule resembles the extrapleural sign in the lung, with its base directed against the compressed cortex. Renal tumor has been reported as the most common cause of spontaneous subcapsular hematoma,18 so detailed studies are indicated to exneoplasm. Severe renal clude underlying tamponade may significantly compromise renal function1’11’25 or induce hypertension by extrinsic compression of renal parenchyma with resultant impairment of renal perfusion (the Page kidney).67 14,l6 INFLAMMATORY
CYSTS
Pyogenic
Hematogenous dissemination of bacteria, particularly Eschen’chia coli, Proteus, Staphyloccus 155
156
Fig. 1. obliterates normal.
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lntrarenal hematoma following trauma. Left: A lower pole mass impresses the inferior aspect of the pelvis and the inferior calyx (arrows). Right: Repeat urogram after 11 days. The mass has disappeared and the kidney is
aureus, Pseudomonas, and Streptococcus fecalis, may result in a septic embolus in the renal cortex. Suppuration may ensue, forming a renal abscess. This may enlarge by extension or by coalescence of multiple contiguous areas developing into a renal carbuncle. The abscess may spontaneously evacuate into the pelvicalyceal system, the perinephric space or through formation of a pseudocapsule, remain contained within the kidney. The ragged outline of the communicating abscess(Fig. 3) differentiates it from the smooth contour of the
communicating cyst. The rare instance of necrotic hypernephroma rupturing into the renal pelvis may be indistinguishable. The angiographic features of a renal inflammatory mass bear much similarity to those of hypernephroma. However, the absence of tumor vessels and the recently emphasized loss of normal corticomedullary junction with alternating lines of lucency and density in the nephrographic phase‘,‘* favor renal infection (Fig. 4). Impaired renal function may be found as a feature of both
Fig. 2. Extrinsic pressure from a subcapsular hematoma. Note the concavity of the underlying cortex of the right kidney.
Fig. 3. epithelium
Upper pole abscess of the superior calyx.
that has breac :hed the Note the ragged outline.
Fig. 4. Renal carbuncle: A thick-walled poorly visualized mass occupies the upper two-thirds of the kidney. Although no definite tumor vessels are seen, differentiation from hypernephroma is difficult. Loss of the normal corticomedullary junction and alternating lines of lucency and density in the lower pole suggest an inflammatory etiology.
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diseases, in neoplasm from renal vein thrombosis and in severe renal infection from cortical arteriolar vasoconstriction and redistribution of blood flow.‘D Tuberculous Tubercle bacilli, generally blood-borne from a primary site in the lung and less frequently from a tuberculous focus in a bone or joint, may form a tubercle at the glomerulus or its regional arterioles. The incidence of bilateral involvement is high in autopsy statistics, whereas unilateral evidence of renal tuberculosis predominates in clinical data. The cortical tubercle, which is the earliest manifestation, heals with a small fibrotic scar undetectable by urography and angiography. When, by reason of either diminished host response, increased virulence of the infecting bacilli, or lack of response to chemotherapy, the initial focus fails to heal or becomes reactivated, the bacilli seed through the renal tubules, forming secondary tubercles, especially at the hairpin turn of the loop of Henle. If the medullary lesion progressesto caseation and ulceration, a necrotic focus develops,7 usually with calyceal distortion. This focus may involve single or multiple papillae and may progress to ulceration of the entire pyramid, several adjoining pyramids or the entire kidney. Healing occurs by fibrosis and calcification, with strictures developing in the collecting system and ureter. The radiographic findings closely parallel the severity of the disease and run the gamut from necrotizing papillitis to autonephrectomy (Fig. 5). Urography and nephrotomography occasionally reveal cystlike lesions; these are seen in various stages of the disease and are attributable to a dilated calyx secondary to infundibular stricture; a communicating abscessthat drains into a calyx; a rounded cortical tuberculoma; or an end-stage pyonephrosis or autonephrectomy. The cystlike tuberculous cavity is generally irregular in contour. Calcification is present in approximately 15%. Angiographic findings vary from an arteritis to the moderate increase in vascularity seen in abscesses. Tuberculous lesions are seldom confused with simple cyst. Papillmy Necrosis In papillary necrosis (necrotizing papillitis, medullary necrosis) the common denominator is necrosis of the renal medulla involving one or more
Fig. 5. Autonephrectomy from tuberculosis. Renal cavitation and ureteral ulceration were followed by caseation, fibrosis, stricture, hydronephrosis, and calcification. This nonfunctioning calcified kidney represents the endstage of obstruction from renal tuberculosis. lCourtesy of Lippincott 81 Co. 15 )
papilla of one or both kidneys. The necrotic papilla, when dislodged into the neighboring calyx, leaves a communicating cavity requiring differentiation from renal tuberculosis, communicating cyst, calyceal diverticulum, and medullary sponge kidney. The necrotic papilla may remain in situ, preserving the normal calyceal configuration,” in which case the radiographic diagnosis is possible only if calcification is visible at the rim of the papilla (Fig. 6). Necrosis in situ is said to be most common in analgesic abuse. Diabetes,’ pyelonephritis,3 hydronephrosis,’ analgesic abuse,” interstitial sclerosis, sickle cell anemia,23 and renal vein thrombosis have all been implicated as a cause of papillary necrosis. A single pathogenesis is not applicable to all reported cases. The radiographic signs may consist of one or more of the following: (1) Contrast medium extending from the fornix of a calyx in a curvilinear line into the cleavage plane. (2) Contrast in a small or large cavity in the papilla. (3) Phlebolith-like calcification in the papilla.
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Fig. 6. Papillary necrosis. The necrotic papilla (arrow) in the lower pole remains in situ and has calcified at its rim, mimicking a phlebolith.
(4) Dilated calyx that extends into the destroyed papilla. Differentiation of papillary necrosis from medullary sponge kidney is made on the basis of the multiplicity of locules in the ectatic tubules of the ducts of Bellini in medullary sponge kidney, in contrast to the single cavity seen in papillary necrosis. The calyceal diverticulum is characteristically limited to one or at most two per kidney, measures 1 or 2 cm in maximum diameter, is smooth walled, and is derived from the adjacent fornix by a slender infundibulum which may be visualized on urography. Differentiation of papillary necrosis from the necrotizing papiliitis of tuberculosis may not be possible without urine culture to substantiate tuberculosis or the screening of urinary sediment for the sequestered papilla of papillary necrosis. Parasitic Echinococcus cyst is the commonest parasitic cyst. In the human the ingested egg of Echinococcus granulosus passesfrom the duodenum into the
portal and pulmonary capillaries. In approximately 2% of the patients, it lodges in the kidney via the arterial route. The encysted embryo is usually found as a single focus in the kidney, polar in location, occasionally calcified, and with varying urographic features depending upon the presence and degree of calyceal communication. The cyst is composed of an inner germinal layer (the endocyst with its budding scolices) surrounded by a laminated membrane (the ectocyst) which is enveloped by an adventitia or pericyst representing the renal reaction to the developing cyst. Calcification, when present, involves the pericyst, in which case it may be curvilinear or amorphous. It is sometimes associated with calcified degenerated daughter cysts within the cyst lumen.15 The lesion may present in the kidney as a closed cyst, “pseudo open” cyst, or open cyst. A closed cyst without calyceal communication presents as a spherical thick walled cyst which may compress the adjacent calyxes and mimic other space occupying lesions. Degeneration of the pericyst permits communication between the calyx and the
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Fig. 7. Renal echinococcal cyst. Tomogram of a “pseudo open” cyst. Degeneration of the pericyst has opened the potential space between the pericyst and ectocyst to opacification by contrast medium in the adjacent calyx. Complete encirclement of the cyst in this manner is unusual.
potential space between the pericyst and the ectocyst (Fig. 7) simulating an open cyst. The extent of opacification on urography depends upon the degree of degeneration of the pericyst and the underlying ectocyst. Rupture of all three cyst layers results in free communication between calyx and cyst lumen thus forming the open cyst (Fig. 8). The filled cyst may be quite irregular, depending on the number of daughter cysts contained within its lumen. NEOPLASM
Qatic Tumor; Necrotic Tumor A tumor simulating a cyst may be solid or cystic. The solid tumor that is confused with cyst presents as an avascular mass because the tumor is either intrinsically avascular or presents as an avascular mass as a result of extensive venous thrombosis. A cystic tumor is most commonly the result of tumor necrosis. Avascularity or minimal vascularity has been reported in from 6% to 22%24 of all renal
carcinomas (Fig. 9). With attention to small vessel detail, the figure should be far lower. Tumor necrosis producing a cystlike lesion can usually be diagnosed by a combination of angiography and cyst puncture with aspiration. The pertinent findings include marginal vascularity, thick rim, irregular contour of the lesion, bloody tap, and typical tumor criteria in the “cyst” aspirate. Occasionally a tumor presents in the wall of a cyst (Fig. 10). l3 It is believed that the tumor produces obstruction of neighboring nephrons and local ischemia, leading to the formation of a cyst. In such cases, the tumor is usually adjacent to the renal parenchyma rather than in the peripheral part of the cyst. It probably occurs in less than 1% of all cysts. The diagnosis is better made by cyst puncture and aspiration than by angiography. Primary cystic non-necrotic tumor is rare and usually proves to be cystadenoma of the renal cortex (Fig. 11). It consists of the papillary type of adenoma and is composed of cystic spaceswith varying degrees of papillary projections on con-
Fig 8. Renal echinococcal cyst. All threecyst layer ‘s have degenerated allowing free communication between the calyx and cyst lumen. The multiple filling defects within the cyst represent retained scolices. (Courtesy of Lippincott & Co.” 1
hypernephroma. The curvilinear calFig. 9. Necrotic in the lower pole with apparent avascularity is cification and might readily masquerade as a simple cyst. deceptive the patient to The abse rice of a true cyst beak brought surgery.
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nective tissue stalks protruding into the cyst. The neoplasms may therefore be primarily cystic or primarily solid. On angiography, all adenomas tend to be avascular, but the presence of tumor may be suggested by the thick rim surrounding .I 1 rne lesion
F ig. 11. Benign cystadenoma communicating system. This is an extremely the pelvicalyceal occ urrence.
with unusual
COMMUNICATING
AND
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LILIENFELD
LESIONS
Under this heading, we have included the calyteal diverticulum, hydrocalyx, and communicating cyst. The communicating abscess has been dis1 inrrammarory .,-I . . lesions. I cusses>unaer cystic
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Its connection to the collecting system may be visualized in the urogram as a thin stalk. Contrast medium frequently remains in the diverticulum after the collecting system has emptied. Because of this poor drainage, infection and calculi within the diverticula are fairly frequent.17 Hydrocalyx
Fig. 12. Calyceal diverticulum. The smoothly contoured collection adjacent to the fornix of an intact calyx fills on retrograde pyelogram. (Courtesy of Lippincott & Co.‘S)
Calyceal Diverticultim The origin of calyceal diverticulum (pyelogenic cyst) is not entirely clear. It has been suggested that it arises from a Wolffian duct remnant which has persisted and dilated, but has not joined with the functioning nephrons.2*6”7 The diverticulum is, therefore, part of the collecting system and communicates with a calyx or infundibulum. It fills on the retrograde, as well as the intravenous pyelogram. The adjacent calyx is normal in appearance (Fig. 12) which helps to distinguish it from communicating cyst or hydrocalyx. Unlike simple cyst or abscess,the mucosa consists of transitional cell epithelium, The diverticulum is usually single and under 2 cm in diameter.
Fig. 13. Hydrocalyx. In contrast to calyceal diverticulum, the dilated calyx bears no relation to a neighboring calyx and is located at a site corresponding to an intact calyx in the left kidney. Faintly opacified calculi are contained within its lumen.
Hydrocalyx (Fig. 13) represents a dilated peripheral calyx secondary to stricture of the infundibulum, either acquired or congenital (muscle ring). It may be multiple and, rarely, quite large. Both the calyceal diverticulum and hydrocalyx tend to fill on urography. The presence of an adjacent normal minor calyx usually differentiates the two; i.e., the diverticulum fills from a normal calyx, but the hydrocalyx is the calyx. Communicating Cyst Rarely, a simple cyst will communicate with a calyx and fill on routine contrast studies. It shows a smooth wall. The cyst has eroded into the calyx and the calyx itself is deformed or obliterated. If infection is present, this represents a communicating abscess,and the cavity is irregular and contains pus. PARARENAL
CYSTS
Parapelvic (Peripelvic) Cyst The preferred term for extraparenchymal cysts occurring in the region of the renal hilus is parapelvic cyst.4 Most cysts in the peripelvic region which displace the renal pelvis are simple serous cysts arising from the renal parenchyma. True parapelvic cysts are rare. The majority are small,
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Fig. 14. Parapelvic cyst. A sharply defined mass (arrows) arises from the renal hilus, projecting medially and displacing the kidney laterally.
but occasionally large cysts have been reported. They probably have more than one cause. It has been suggested that lymphatic ectasia, possibly secondary to chronic inflammatory changes, may produce a lymphatic cyst.** Other cysts may arise on a congenital basis from an embryonic rest (Wolffian duct remnant). Parapelvic cyst (Fig. 14) may produce marked lateral renal displacement with rotation of the kidney and lateral displacement of the proximal ureter. It rarely produces obstruction. Occasionally it compresses the hilar fat, producing a thin, lucent fat line” separating the cyst from the renal parenchyma. Pararenal Pseudocyst This is also called urinoma, hydrocele renalis, pararenal pseudohydronephrosis, and perinephric cyst. It represents the fibrous encapsulation of chronically extravasated urine and occurs most commonly in the perinephric compartment of the retroperitoneum. Trauma, surgery, or instrumentation are the most common precursors. Transient urinary extravasation secondary to forniceal rupture from an acutely impacted calculus is not accompanied by pseudocyst formation. Infection does not appear to play a significant role since the cyst content is usually sterile, and the patient is afebrile, presenting primarily with complaints related to a gradually increasing flank mass. Urine in the retroperitoneum is usually rapidly resorbed, but chronic extravasation results in lysis of retroperitoneal fat,’ reactive fibrosis, and pseudocyst formation. The pressure of urine within the
Fig. 15. Pararenal pseudocyst. Three weeks after pyelolithotomy. The kidney is displaced superiorly and laterally with concomitant displacement of the ureter. Opacification of the cyst lumen as seen here is unusual. (Courtesy of Lippincott & Co.*s)
pseudocyst probably acts to reduce further extravasation, so that cyst grows slowly and urographic opacification of its lumen is infrequent (Fig. 15). Location of the pseudocyst depends upon the site of leakage, pre-existing fibrosis in the retroperitoneum, and whether the perirenal fascia has been opened by previous surgery. Pseudocyst secondary to extravasation from the renal hilus (renal pelvis surgery, chronic ureteral obstruction) tends to localize inferomedial to the kidney, displacing it superiorly and laterally. Urine extravasating through the lateral cortex (trauma, surgery) tends to localize inferior, posterior, and lateral to the kidney displacing the kidney in the opposite direction. Previous surgical intervention or perinephric infection tends to compartmentalize the pseudocyst in the perirenal space. Rarely subcapsular pseudocyst may occur. The urographic findings vary according to the cause and localization. They include a mass displacing the kidney, distortion of renal outline and calyceal pattern, nonfunction from pressure or obstruction, and filling of pseudocyst with contrast medium (unusual). REFERENCES 1. Aschner PW, Klinger ME: Subcapsular renal hemorrhage causing anuria of single kidney. .I Urol65:777-780, 1951
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2. Davidson AJ, Talner LB: Urographic and angiographic abnormalities in adult-onset acute bacterial nephritis. Radiology 106:249-256, 1973 3. Edmondson HA, Martin HE, Evans NG: Necrosis of renal papillae and acute pyelonephritis in diabetes mellitus. Arch Intern Med 79:148-175, 1947 4. Elkin M, Bernstein J: Cystic disease of the kidneyRadiological and pathological considerations. Clin Radio1 20:65-82,1969 5. Emmett JL, Witten DM: Clinical Urography: An Atlas
and Textbook of Roentgenologic Diagnosis. (ed. 3) Vol. 2. Philadelphia, Saunders, 1971, pp 1033 6. Engel WJ, Page IH: Hypertension due to renal compression from subcapsular hematoma. J Urol73:735-739, 1955 7. Friedman JJ, Selkurt EE: Circulation in specific organs, in Selkurt EE (ed): Physiology. Boston, Little, Brown, 1966. pp 395-396 8. Harrow BR: Nephropathy of diabetes with emphasis on papillary necrosis. Postgrad Med 37:A-63-69, 1965 9. Harrow BR: Renal papillary necrosis: A critique of pathogenesis. J Urol97:203-208, 1967 10. Hill GS, Clark RL: A comparative angiographic, microangiographic and histologic study of experimental pyelonephritis. Invest Radio1 7:33-47, 1972 11. Koehler PR, Tamer LB, Friedenberg MJ, et al: Association of subcapsular hematomas with the nonfunctioning kidney. Radiology 106:537-542, 1973 12. Koehler PR: The roentgen diagnosis of renal inflammatory masses-Special emphasis on angiographic changes. Radiology 112: 257-266, 1974 13. Lang EK: Coexistence of cyst and tumors in the same kidney. Radiology 101:7-16, 1971 14. Marshall WH Jr, Castellino RA: Hypertension produced by constricting capsular renal lesions (“Page” kidney). Radiology 101:561-565, 1971
15. Ney C, Friedenberg RM: Cysts of the kidney, in Ney C, Friedenberg RM (ed): Radiographic Atlas of the Genitourinary System. Philadelphia, JB Lippincott, 1966, PP 205 16. Page IH: Production of persistent arterial hypertension by cellophane perinephritis. JAMA 113:20462048,1939
17. Pfister PC, Middleton AW Jr: Pyelo-calyceal diverticulum: embryogenic, anatomic and clinical characteristics. J Urol 111: 2-6, 1974 18. Polldck HM, Popky GL: Roentgenographic manifestations of spontaneous renal hemorrhage. Radiology llO:l-6, 1974 19. Poynter JD, Hare WSC: Necrosis in situ: A form of renal papillary necrosis seen in analgesic nephropathy. Radiology 111:69-76, 1974 20. Ranninger K, Abrams E, Borden TA: Pseudotumor resulting from a fresh renal infarct. Radiology 92:343344,1969
21. Shapiro R: Peripelvic renal cyst. Case report with a diagnostic roentgen sign. Am J Roentgen01 90:81-82, 1963 22. Thompson IM: Peripelvic lymphatic renal cysts. J Urol78:343-350, 1957 23. Vix VA: Urographic demonstration of renal medullary necrosis in hemoglobin SA and SC disease. Radiology 85:320-324, 1965 24. Watson RC, Fleming RJ, Evans JA: Arteriography in the diagnosis of renal carcinoma: Review of 100 cases. Radiology 91:888-897, 1968 25. Waugh WH, Hamilton WF: The physical effects of increased venous and extrarenal pressure on renal vascular resistance. Circul Research 6:116-121,1958 26. Holm H: On pyelogenic renal cysts. Acta Radio1 29:87-94,1948
M.D., and Ralph M. Lilienfeld,
A
CQUIRED CYSTIC LESIONS of the kidney are the product of several diseases of different etiology and are usually readily distinguished from the renal cysts discussed elsewhere in this Seminar. These acquired lesions are, in fact, cavities that have formed within or adjacent to the renal parenchyma, and they are variously lined by fibrous tissue, necrotic tumor, endothelium, or necrotic or intact epithelium, depending upon their cause and stage of evolution. These acquired lesions are best classified by etiology. (1) Cystic hematomas (a) traumatic (b) spontaneous (2) Inflammatory cysts (a) pyogenic (b) tuberculous (c) papillary necrosis (d) parasitic (3) Cystic neoplasms (4) Communicating cystic lesions (a) calyceal diverticulum (b) hydrocalyx (c) communicating cyst (5) Pararenal cysts (a) parapelvic (b) pararenal pseudocyst CYSTIC
HEMATOMAS
Renal hemorrhage may be traumatic or spontaneous in origin. Spontaneous hemorrhage occurs secondary to the administration of anticoagulants, a bleeding diathesis, vascular erosion by tumor, vasculitis from drug abuse, embolic infarction2’ and occasionally from undetermined cause. Depending upon the site and extent of bleeding, the accumulated blood may either seep into the renal tubules, breech the pelvicalyceal system (with resulting hematuria), or extravasate through the Richard M. Friedenberg, M.D.: Professor and Chairman, Department of Radiology, New York Medical CollegeMetropolitan Hospital Center, New York, N. Y. 10029; Ralph M. Lilienfeld, M.D.: Associate Professor, Department of Radiology, New York Medical College-Metropolitan Hospital Center, New York, N. Y. 10029. o 1975 by Grune & Stratton, Inc. Seminars
in Roentgenology,
Vol.
X, No. 2 (April),
1975
M.D.
lacerated capsule to form a perinephric hematoma. Blood contained within the renal parenchyma forms an intrarenal hematoma (Fig. 1); when confined between cortex and capsule it produces a subcapsular hematoma. The hematoma is lucent on nephrotomography and avascular on angiography. The distinguishing hallmark of the intrarenal hematoma is its rapid reversibility.18 In contrast to the simple cyst, the rapidly developing intrarenal hematoma, even when peripherally located, does not form the characteristic beak caused by the slow expansion of the simple cyst, which pulls out the marginal parenchyma. In the vascular phase of nephrotomography or angiography, the hematoma usually presents with a thick marginal rim, mimicking abscessmore than cyst. Calcification, which might be expected as a common feature of intrarenal hematoma, is in our experience unusual, it is more suggestive of tumor, cyst, or abscess. The subcapsular hematoma compresses the relatively unyielding renal parenchyma as it strips the capsule from the cortex. Thus, the convexity of the hematoma is directed away from the kidney with the maximum convexity at the geographic center of the hematoma. The underlying cortex becomes flat or slightly concave (Fig. 2). The capsule, supplied by twigs from the capsular artery is frequently visualized both on nephrotomography and angiography. The displaced capsule resembles the extrapleural sign in the lung, with its base directed against the compressed cortex. Renal tumor has been reported as the most common cause of spontaneous subcapsular hematoma,18 so detailed studies are indicated to exneoplasm. Severe renal clude underlying tamponade may significantly compromise renal function1’11’25 or induce hypertension by extrinsic compression of renal parenchyma with resultant impairment of renal perfusion (the Page kidney).67 14,l6 INFLAMMATORY
CYSTS
Pyogenic
Hematogenous dissemination of bacteria, particularly Eschen’chia coli, Proteus, Staphyloccus 155
156
Fig. 1. obliterates normal.
FRIEDENBERG
AND
LILIENFELD
lntrarenal hematoma following trauma. Left: A lower pole mass impresses the inferior aspect of the pelvis and the inferior calyx (arrows). Right: Repeat urogram after 11 days. The mass has disappeared and the kidney is
aureus, Pseudomonas, and Streptococcus fecalis, may result in a septic embolus in the renal cortex. Suppuration may ensue, forming a renal abscess. This may enlarge by extension or by coalescence of multiple contiguous areas developing into a renal carbuncle. The abscess may spontaneously evacuate into the pelvicalyceal system, the perinephric space or through formation of a pseudocapsule, remain contained within the kidney. The ragged outline of the communicating abscess(Fig. 3) differentiates it from the smooth contour of the
communicating cyst. The rare instance of necrotic hypernephroma rupturing into the renal pelvis may be indistinguishable. The angiographic features of a renal inflammatory mass bear much similarity to those of hypernephroma. However, the absence of tumor vessels and the recently emphasized loss of normal corticomedullary junction with alternating lines of lucency and density in the nephrographic phase‘,‘* favor renal infection (Fig. 4). Impaired renal function may be found as a feature of both
Fig. 2. Extrinsic pressure from a subcapsular hematoma. Note the concavity of the underlying cortex of the right kidney.
Fig. 3. epithelium
Upper pole abscess of the superior calyx.
that has breac :hed the Note the ragged outline.
Fig. 4. Renal carbuncle: A thick-walled poorly visualized mass occupies the upper two-thirds of the kidney. Although no definite tumor vessels are seen, differentiation from hypernephroma is difficult. Loss of the normal corticomedullary junction and alternating lines of lucency and density in the lower pole suggest an inflammatory etiology.
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diseases, in neoplasm from renal vein thrombosis and in severe renal infection from cortical arteriolar vasoconstriction and redistribution of blood flow.‘D Tuberculous Tubercle bacilli, generally blood-borne from a primary site in the lung and less frequently from a tuberculous focus in a bone or joint, may form a tubercle at the glomerulus or its regional arterioles. The incidence of bilateral involvement is high in autopsy statistics, whereas unilateral evidence of renal tuberculosis predominates in clinical data. The cortical tubercle, which is the earliest manifestation, heals with a small fibrotic scar undetectable by urography and angiography. When, by reason of either diminished host response, increased virulence of the infecting bacilli, or lack of response to chemotherapy, the initial focus fails to heal or becomes reactivated, the bacilli seed through the renal tubules, forming secondary tubercles, especially at the hairpin turn of the loop of Henle. If the medullary lesion progressesto caseation and ulceration, a necrotic focus develops,7 usually with calyceal distortion. This focus may involve single or multiple papillae and may progress to ulceration of the entire pyramid, several adjoining pyramids or the entire kidney. Healing occurs by fibrosis and calcification, with strictures developing in the collecting system and ureter. The radiographic findings closely parallel the severity of the disease and run the gamut from necrotizing papillitis to autonephrectomy (Fig. 5). Urography and nephrotomography occasionally reveal cystlike lesions; these are seen in various stages of the disease and are attributable to a dilated calyx secondary to infundibular stricture; a communicating abscessthat drains into a calyx; a rounded cortical tuberculoma; or an end-stage pyonephrosis or autonephrectomy. The cystlike tuberculous cavity is generally irregular in contour. Calcification is present in approximately 15%. Angiographic findings vary from an arteritis to the moderate increase in vascularity seen in abscesses. Tuberculous lesions are seldom confused with simple cyst. Papillmy Necrosis In papillary necrosis (necrotizing papillitis, medullary necrosis) the common denominator is necrosis of the renal medulla involving one or more
Fig. 5. Autonephrectomy from tuberculosis. Renal cavitation and ureteral ulceration were followed by caseation, fibrosis, stricture, hydronephrosis, and calcification. This nonfunctioning calcified kidney represents the endstage of obstruction from renal tuberculosis. lCourtesy of Lippincott 81 Co. 15 )
papilla of one or both kidneys. The necrotic papilla, when dislodged into the neighboring calyx, leaves a communicating cavity requiring differentiation from renal tuberculosis, communicating cyst, calyceal diverticulum, and medullary sponge kidney. The necrotic papilla may remain in situ, preserving the normal calyceal configuration,” in which case the radiographic diagnosis is possible only if calcification is visible at the rim of the papilla (Fig. 6). Necrosis in situ is said to be most common in analgesic abuse. Diabetes,’ pyelonephritis,3 hydronephrosis,’ analgesic abuse,” interstitial sclerosis, sickle cell anemia,23 and renal vein thrombosis have all been implicated as a cause of papillary necrosis. A single pathogenesis is not applicable to all reported cases. The radiographic signs may consist of one or more of the following: (1) Contrast medium extending from the fornix of a calyx in a curvilinear line into the cleavage plane. (2) Contrast in a small or large cavity in the papilla. (3) Phlebolith-like calcification in the papilla.
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Fig. 6. Papillary necrosis. The necrotic papilla (arrow) in the lower pole remains in situ and has calcified at its rim, mimicking a phlebolith.
(4) Dilated calyx that extends into the destroyed papilla. Differentiation of papillary necrosis from medullary sponge kidney is made on the basis of the multiplicity of locules in the ectatic tubules of the ducts of Bellini in medullary sponge kidney, in contrast to the single cavity seen in papillary necrosis. The calyceal diverticulum is characteristically limited to one or at most two per kidney, measures 1 or 2 cm in maximum diameter, is smooth walled, and is derived from the adjacent fornix by a slender infundibulum which may be visualized on urography. Differentiation of papillary necrosis from the necrotizing papiliitis of tuberculosis may not be possible without urine culture to substantiate tuberculosis or the screening of urinary sediment for the sequestered papilla of papillary necrosis. Parasitic Echinococcus cyst is the commonest parasitic cyst. In the human the ingested egg of Echinococcus granulosus passesfrom the duodenum into the
portal and pulmonary capillaries. In approximately 2% of the patients, it lodges in the kidney via the arterial route. The encysted embryo is usually found as a single focus in the kidney, polar in location, occasionally calcified, and with varying urographic features depending upon the presence and degree of calyceal communication. The cyst is composed of an inner germinal layer (the endocyst with its budding scolices) surrounded by a laminated membrane (the ectocyst) which is enveloped by an adventitia or pericyst representing the renal reaction to the developing cyst. Calcification, when present, involves the pericyst, in which case it may be curvilinear or amorphous. It is sometimes associated with calcified degenerated daughter cysts within the cyst lumen.15 The lesion may present in the kidney as a closed cyst, “pseudo open” cyst, or open cyst. A closed cyst without calyceal communication presents as a spherical thick walled cyst which may compress the adjacent calyxes and mimic other space occupying lesions. Degeneration of the pericyst permits communication between the calyx and the
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Fig. 7. Renal echinococcal cyst. Tomogram of a “pseudo open” cyst. Degeneration of the pericyst has opened the potential space between the pericyst and ectocyst to opacification by contrast medium in the adjacent calyx. Complete encirclement of the cyst in this manner is unusual.
potential space between the pericyst and the ectocyst (Fig. 7) simulating an open cyst. The extent of opacification on urography depends upon the degree of degeneration of the pericyst and the underlying ectocyst. Rupture of all three cyst layers results in free communication between calyx and cyst lumen thus forming the open cyst (Fig. 8). The filled cyst may be quite irregular, depending on the number of daughter cysts contained within its lumen. NEOPLASM
Qatic Tumor; Necrotic Tumor A tumor simulating a cyst may be solid or cystic. The solid tumor that is confused with cyst presents as an avascular mass because the tumor is either intrinsically avascular or presents as an avascular mass as a result of extensive venous thrombosis. A cystic tumor is most commonly the result of tumor necrosis. Avascularity or minimal vascularity has been reported in from 6% to 22%24 of all renal
carcinomas (Fig. 9). With attention to small vessel detail, the figure should be far lower. Tumor necrosis producing a cystlike lesion can usually be diagnosed by a combination of angiography and cyst puncture with aspiration. The pertinent findings include marginal vascularity, thick rim, irregular contour of the lesion, bloody tap, and typical tumor criteria in the “cyst” aspirate. Occasionally a tumor presents in the wall of a cyst (Fig. 10). l3 It is believed that the tumor produces obstruction of neighboring nephrons and local ischemia, leading to the formation of a cyst. In such cases, the tumor is usually adjacent to the renal parenchyma rather than in the peripheral part of the cyst. It probably occurs in less than 1% of all cysts. The diagnosis is better made by cyst puncture and aspiration than by angiography. Primary cystic non-necrotic tumor is rare and usually proves to be cystadenoma of the renal cortex (Fig. 11). It consists of the papillary type of adenoma and is composed of cystic spaceswith varying degrees of papillary projections on con-
Fig 8. Renal echinococcal cyst. All threecyst layer ‘s have degenerated allowing free communication between the calyx and cyst lumen. The multiple filling defects within the cyst represent retained scolices. (Courtesy of Lippincott & Co.” 1
hypernephroma. The curvilinear calFig. 9. Necrotic in the lower pole with apparent avascularity is cification and might readily masquerade as a simple cyst. deceptive the patient to The abse rice of a true cyst beak brought surgery.
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nective tissue stalks protruding into the cyst. The neoplasms may therefore be primarily cystic or primarily solid. On angiography, all adenomas tend to be avascular, but the presence of tumor may be suggested by the thick rim surrounding .I 1 rne lesion
F ig. 11. Benign cystadenoma communicating system. This is an extremely the pelvicalyceal occ urrence.
with unusual
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Under this heading, we have included the calyteal diverticulum, hydrocalyx, and communicating cyst. The communicating abscess has been dis1 inrrammarory .,-I . . lesions. I cusses>unaer cystic
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Its connection to the collecting system may be visualized in the urogram as a thin stalk. Contrast medium frequently remains in the diverticulum after the collecting system has emptied. Because of this poor drainage, infection and calculi within the diverticula are fairly frequent.17 Hydrocalyx
Fig. 12. Calyceal diverticulum. The smoothly contoured collection adjacent to the fornix of an intact calyx fills on retrograde pyelogram. (Courtesy of Lippincott & Co.‘S)
Calyceal Diverticultim The origin of calyceal diverticulum (pyelogenic cyst) is not entirely clear. It has been suggested that it arises from a Wolffian duct remnant which has persisted and dilated, but has not joined with the functioning nephrons.2*6”7 The diverticulum is, therefore, part of the collecting system and communicates with a calyx or infundibulum. It fills on the retrograde, as well as the intravenous pyelogram. The adjacent calyx is normal in appearance (Fig. 12) which helps to distinguish it from communicating cyst or hydrocalyx. Unlike simple cyst or abscess,the mucosa consists of transitional cell epithelium, The diverticulum is usually single and under 2 cm in diameter.
Fig. 13. Hydrocalyx. In contrast to calyceal diverticulum, the dilated calyx bears no relation to a neighboring calyx and is located at a site corresponding to an intact calyx in the left kidney. Faintly opacified calculi are contained within its lumen.
Hydrocalyx (Fig. 13) represents a dilated peripheral calyx secondary to stricture of the infundibulum, either acquired or congenital (muscle ring). It may be multiple and, rarely, quite large. Both the calyceal diverticulum and hydrocalyx tend to fill on urography. The presence of an adjacent normal minor calyx usually differentiates the two; i.e., the diverticulum fills from a normal calyx, but the hydrocalyx is the calyx. Communicating Cyst Rarely, a simple cyst will communicate with a calyx and fill on routine contrast studies. It shows a smooth wall. The cyst has eroded into the calyx and the calyx itself is deformed or obliterated. If infection is present, this represents a communicating abscess,and the cavity is irregular and contains pus. PARARENAL
CYSTS
Parapelvic (Peripelvic) Cyst The preferred term for extraparenchymal cysts occurring in the region of the renal hilus is parapelvic cyst.4 Most cysts in the peripelvic region which displace the renal pelvis are simple serous cysts arising from the renal parenchyma. True parapelvic cysts are rare. The majority are small,
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Fig. 14. Parapelvic cyst. A sharply defined mass (arrows) arises from the renal hilus, projecting medially and displacing the kidney laterally.
but occasionally large cysts have been reported. They probably have more than one cause. It has been suggested that lymphatic ectasia, possibly secondary to chronic inflammatory changes, may produce a lymphatic cyst.** Other cysts may arise on a congenital basis from an embryonic rest (Wolffian duct remnant). Parapelvic cyst (Fig. 14) may produce marked lateral renal displacement with rotation of the kidney and lateral displacement of the proximal ureter. It rarely produces obstruction. Occasionally it compresses the hilar fat, producing a thin, lucent fat line” separating the cyst from the renal parenchyma. Pararenal Pseudocyst This is also called urinoma, hydrocele renalis, pararenal pseudohydronephrosis, and perinephric cyst. It represents the fibrous encapsulation of chronically extravasated urine and occurs most commonly in the perinephric compartment of the retroperitoneum. Trauma, surgery, or instrumentation are the most common precursors. Transient urinary extravasation secondary to forniceal rupture from an acutely impacted calculus is not accompanied by pseudocyst formation. Infection does not appear to play a significant role since the cyst content is usually sterile, and the patient is afebrile, presenting primarily with complaints related to a gradually increasing flank mass. Urine in the retroperitoneum is usually rapidly resorbed, but chronic extravasation results in lysis of retroperitoneal fat,’ reactive fibrosis, and pseudocyst formation. The pressure of urine within the
Fig. 15. Pararenal pseudocyst. Three weeks after pyelolithotomy. The kidney is displaced superiorly and laterally with concomitant displacement of the ureter. Opacification of the cyst lumen as seen here is unusual. (Courtesy of Lippincott & Co.*s)
pseudocyst probably acts to reduce further extravasation, so that cyst grows slowly and urographic opacification of its lumen is infrequent (Fig. 15). Location of the pseudocyst depends upon the site of leakage, pre-existing fibrosis in the retroperitoneum, and whether the perirenal fascia has been opened by previous surgery. Pseudocyst secondary to extravasation from the renal hilus (renal pelvis surgery, chronic ureteral obstruction) tends to localize inferomedial to the kidney, displacing it superiorly and laterally. Urine extravasating through the lateral cortex (trauma, surgery) tends to localize inferior, posterior, and lateral to the kidney displacing the kidney in the opposite direction. Previous surgical intervention or perinephric infection tends to compartmentalize the pseudocyst in the perirenal space. Rarely subcapsular pseudocyst may occur. The urographic findings vary according to the cause and localization. They include a mass displacing the kidney, distortion of renal outline and calyceal pattern, nonfunction from pressure or obstruction, and filling of pseudocyst with contrast medium (unusual). REFERENCES 1. Aschner PW, Klinger ME: Subcapsular renal hemorrhage causing anuria of single kidney. .I Urol65:777-780, 1951
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2. Davidson AJ, Talner LB: Urographic and angiographic abnormalities in adult-onset acute bacterial nephritis. Radiology 106:249-256, 1973 3. Edmondson HA, Martin HE, Evans NG: Necrosis of renal papillae and acute pyelonephritis in diabetes mellitus. Arch Intern Med 79:148-175, 1947 4. Elkin M, Bernstein J: Cystic disease of the kidneyRadiological and pathological considerations. Clin Radio1 20:65-82,1969 5. Emmett JL, Witten DM: Clinical Urography: An Atlas
and Textbook of Roentgenologic Diagnosis. (ed. 3) Vol. 2. Philadelphia, Saunders, 1971, pp 1033 6. Engel WJ, Page IH: Hypertension due to renal compression from subcapsular hematoma. J Urol73:735-739, 1955 7. Friedman JJ, Selkurt EE: Circulation in specific organs, in Selkurt EE (ed): Physiology. Boston, Little, Brown, 1966. pp 395-396 8. Harrow BR: Nephropathy of diabetes with emphasis on papillary necrosis. Postgrad Med 37:A-63-69, 1965 9. Harrow BR: Renal papillary necrosis: A critique of pathogenesis. J Urol97:203-208, 1967 10. Hill GS, Clark RL: A comparative angiographic, microangiographic and histologic study of experimental pyelonephritis. Invest Radio1 7:33-47, 1972 11. Koehler PR, Tamer LB, Friedenberg MJ, et al: Association of subcapsular hematomas with the nonfunctioning kidney. Radiology 106:537-542, 1973 12. Koehler PR: The roentgen diagnosis of renal inflammatory masses-Special emphasis on angiographic changes. Radiology 112: 257-266, 1974 13. Lang EK: Coexistence of cyst and tumors in the same kidney. Radiology 101:7-16, 1971 14. Marshall WH Jr, Castellino RA: Hypertension produced by constricting capsular renal lesions (“Page” kidney). Radiology 101:561-565, 1971
15. Ney C, Friedenberg RM: Cysts of the kidney, in Ney C, Friedenberg RM (ed): Radiographic Atlas of the Genitourinary System. Philadelphia, JB Lippincott, 1966, PP 205 16. Page IH: Production of persistent arterial hypertension by cellophane perinephritis. JAMA 113:20462048,1939
17. Pfister PC, Middleton AW Jr: Pyelo-calyceal diverticulum: embryogenic, anatomic and clinical characteristics. J Urol 111: 2-6, 1974 18. Polldck HM, Popky GL: Roentgenographic manifestations of spontaneous renal hemorrhage. Radiology llO:l-6, 1974 19. Poynter JD, Hare WSC: Necrosis in situ: A form of renal papillary necrosis seen in analgesic nephropathy. Radiology 111:69-76, 1974 20. Ranninger K, Abrams E, Borden TA: Pseudotumor resulting from a fresh renal infarct. Radiology 92:343344,1969
21. Shapiro R: Peripelvic renal cyst. Case report with a diagnostic roentgen sign. Am J Roentgen01 90:81-82, 1963 22. Thompson IM: Peripelvic lymphatic renal cysts. J Urol78:343-350, 1957 23. Vix VA: Urographic demonstration of renal medullary necrosis in hemoglobin SA and SC disease. Radiology 85:320-324, 1965 24. Watson RC, Fleming RJ, Evans JA: Arteriography in the diagnosis of renal carcinoma: Review of 100 cases. Radiology 91:888-897, 1968 25. Waugh WH, Hamilton WF: The physical effects of increased venous and extrarenal pressure on renal vascular resistance. Circul Research 6:116-121,1958 26. Holm H: On pyelogenic renal cysts. Acta Radio1 29:87-94,1948
