Distinction Between Perirenal and Subcapsular Collections

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Abscesses or hematomas in the perirenal space and in the subcapsular region of the kidney can simulate each other and a host of other conditions closely. Identification of their specific localization may be very important in the clinical diagnosis and in determining the most appropriate therapy. Advances in establishing the characteristic features of abscesses or hematomas are based on the anatomic structures that define their collection.11

Anatomic Considerations. The renal capsule (Fig. 8158) is a thin tunic that forms an intimate, firm, smooth investment for the kidney. It is composed predomi nantly of fibrous tissue, but there is some smooth muscle within its inner layer. No adipose tissue is found between the renal parenchyma and the capsule. The capsule can be stripped off easily; when this is done, numerous fine processes of connective tissue and small blood vessels are torn through.

The capsular arteries course through and supply primarily the perirenal fat, which is located between the renal capsule and the renal fascia. The somewhat confusing designation of these vessels as "capsular" is apparently derived from the old nomenclature of the perirenal fat as the "adipose capsule of the kidney." They are composed of three basic pathways: superior, middle (recurrent and perforating), and inferior capsular arteries. A prominent arterial arcade is formed within the

Capsular Artery

Fig. 8—158. Normal relationships of investing structures of kidney and major findings distinguishing a perirenal from a subcapsular collection.

Note particularly the relationships of the displaced renal capsule, perirenal fascia, and capsular arteries at the borders of the mass. Flattening of the underlying renal parenchyma is more commonly found in subcapsular collections. (From Meyers et al.11)

Fig. 8—158. Normal relationships of investing structures of kidney and major findings distinguishing a perirenal from a subcapsular collection.

Note particularly the relationships of the displaced renal capsule, perirenal fascia, and capsular arteries at the borders of the mass. Flattening of the underlying renal parenchyma is more commonly found in subcapsular collections. (From Meyers et al.11)

perirenal fat lateral to the kidney that communicates with renal branches perforating through the capsule.

Etiology and Pathogenesis. Perirenal abscesses, as we have seen, are almost invariably secondary to a site of renal infection that perforates through the capsule to contaminate the perirenal fatty compartment.

Extrarenal hematomas, whether subcapsular or peri-renal in location, are generally considered either traumatic or spontaneous (nontraumatic). In a classic review of the world literature in 1933, Polkey and Vynalek161 reported a comprehensive study of the causes of spontaneous hematomas. Of 178 cases reviewed, the location was subcapsular in 18.5% and extracapsular (perirenal or pararenal or a combination of the two) in 81.5%. Lesions of the kidneys and its blood vessels accounted for 92% of the cases. The underlying etiologies, in the order of their relative frequencies, included nephritis, neoplasms, aneurysms of the renal artery, arteriosclerosis, hydro-nephrosis, periarteritis nodosa, tuberculosis, renal cysts, and blood dyscrasias.

An increasing number of cases of extrarenal hemorrhage owing to periarteritis nodosa and occult, often surprisingly small, renal tumors have been reported.180-185 Many of the earlier cases diagnosed as nephritis may have actually been periarteritis nodosa or lupus ery-thematosus. Current experience with spontaneous sub-capsular or perirenal hematomas indicates that renal cell carcinoma and renal angiomyolipoma are the cause in 30-60%180,l86; the remaining cases are caused by a variety of vascular, inflammatory, cystic, and hematologic disorders.186

Rarely, metastatic disease to the kidneys, especially from vascular tumors such as choriocarcinoma, can cause perirenal hemorrhage.187 Melanoma and lung cancer tend to involve the kidney and perirenal space con-

188,189

tiguously, but these do not tend to hemorrhage.

Percutaneous renal biopsy results in subcapsular hematoma in approximately 28% and in some degree of perirenal hemorrhage in over 90% of patients. Very few of these hematomas, however, are clinically significant.190-192 Subcapsular hematomas have been identified in 15% of patients after extracorporeal shock wave lith-

otripsy. 9

One mechanism of hematoma formation begins with cortical infarcts.184 The hemorrhage may be confined by the relatively rigid capsule; at other times the blood breaks through the capsule immediately but is confined within the dimensions of the renal fascia. A hematoma within the distensible perirenal compartment can develop to an enormous size before pressure becomes sufficient to cause tamponade of the bleeding site.

The spread of hemorrhage from ruptured abdominal aortic aneurysms depends upon the anatomic level and site of leaking and the amount of extravasated blood. At the level of the kidneys, the aorta lies behind the anterior renal fascia. Thus, aortic bleeding occurs most commonly directly into the perirenal space.194—196 In ruptured abdominal aortic aneurysms, a localized disruption of the calcified or noncalcified wall of the aneurysm is identifiable by CT and indicates the site of extravasation (Fig. 8—159). Aortic wall indistinctness, however, is not always a specific indication of rupture.196,197 The extent of lack of conspicuity of the portion of wall seen on CT is generally greater than the true extent of any rupture.198 On CT, a crescent of increased attenuation is a reliable sign of acute or impending rupture.199,200 Rarely, an aortic aneurysm may rupture into the inferior vena cava resulting in a high-output aortocaval fistula201—203 (Fig. 8—160). Color Doppler sonography may demonstrate the actual site of the fistula to the distended cava in selected patients.

Clinical Signs and Symptoms. The clinical diagnosis of subcapsular or perirenal abscess or bleeding is rarely made. Signs and symptoms are often subtle, delayed, nonspecific, or misleading.

With acute bleeding, the clinical picture may consist of pain, tenderness, and rigidity, which may be associated with nausea, vomiting, and abdominal distention. Concomitant signs of internal bleeding may be present, but this may be manifested only by a drop in hemoglobin or hematocrit. A mass may not be palpable, especially if the hematoma lies posteriorly to the kidney. If

Ruptured Hemorrhagic Aneurysm

Fig. 8-159. Perirenal bleeding from ruptured aneurysm of the abdominal aorta.

Rupture from the posterolateral wall of the aorta (arrows) results in bleeding tracking along the bridging renal septa within the perirenal fat.

Fig. 8-159. Perirenal bleeding from ruptured aneurysm of the abdominal aorta.

Rupture from the posterolateral wall of the aorta (arrows) results in bleeding tracking along the bridging renal septa within the perirenal fat.

the hematoma is subcapsular, it may not become particularly large because of the confining effect of the renal capsule, but occasionally the collection may approximate the size of the kidney itself. With sudden and profuse hemorrhages, many types of retroperitoneal and in-traperitoneal catastrophes may be mimicked. If the hematoma extends downward in the retrocecal region, the patient may be explored for an acute appendicitis.204 Rarely, perforation into the peritoneal cavity may occur, causing a generalized peritonitis or a massive intra-peritoneal hemorrhage.

With subacute or chronic bleeding, pain may not be a conspicuous feature, and the principal findings may be only anemia and, perhaps, a palpable mass.

Hypertension may result from the constrictive renal ii 205-907

effects of a large subcapsular ' or less commonly a perirenal hematoma, producing the Page kidney.208 If the condition is not particularly chronic, the hypertension may be easily corrected by decompression or nephrec-tomy.

Radiologic Findings. Supcapsular or perirenal hemorrhage or abscess can be indicated on plain films or intravenous urography and can be clearly documented by nephrotomography or angiography. While such studies are performed less commonly in the era of sectional imaging, the fundamental changes remain diagnostic. I have shown that localization of the process to a specific extrarenal compartment is based on recognizing characteristic changes involving the renal capsule, renal fascia, kidney margin, and capsular arteries11 (Fig. 8—158).

1. Visualization of the displaced renal capsule or fascia. Either of these structures, displaced outward from the renal margin, can be seen as a striplike density 1—4 mm thick. The renal fascia can be visualized by plain film roentgenography and urography in cases ofperirenal abscess or hematoma (Figs. 8—161 through 8—163). In diffuse processes of the perirenal space, it can be recognized over a considerable length. At times, a displaced renal capsule may be demonstrated by urography (Fig. 8—

Opacification of the displaced renal capsule (Fig. 8—

165) and fascia is achieved in nephrotomography and arteriography.11,183,209,210 Contrast is further afforded by the nonopaque abscess or hematoma on one side and radiolucent fat on the other.

I have noted a type of displacement, which, when present, distinguishes subcapsular from perirenal collections. The renal capsule is sharply deflected over the margin of a subcapsular mass. Even with huge collec-

Fig. 8-160. Aortocaval fistula.

(a) Contrast-enhanced CT shows marked extraperitoneal hemorrhage on the right with gross displacement of the kidney. There is simultaneous enhancement of both the enlarged inferior vena cava (C) and the conspicuous abdominal aorta. Discrepant renal function is noted.

(b) At a lower level, rupture of the calcified abdominal aortic aneurysm into the cava is evident (arrow).

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tions, its point of displacement intimately conforms to the border of the hematoma (Fig. 8-165). It appears that this is a consequence of the relatively rigid, inelastic nature of the renal capsule. In contrast, renal fascia is often displaced laterally from the margin of the kidney at some distance from a coalescent perirenal collection. Its maximum deflection is at the site of the perirenal hematoma or abscess, but it can be seen to depart from close to the renal border both above and below (Fig. 8-161). It is a reflection of the yielding perirenal fat and renal fascia.

At times, simultaneous displacement of both the renal capsule and fascia can be identified (Fig. 8-166).

2. Visualization of the hematoma or abscess. The subcap-sular or perirenal collection is easily seen as a nonopaque mass between the opacified renal parenchyma on one side and the elevated renal capsule or fascia on the other.

This is most often seen in relationship to the lower pole posterolaterally.

3. Flattening and compression of the kidney. While this may occur with tense perirenal collections, it is more typical of subcapsular hematoma. The pressure exerted by a confined subcapsular hematoma typically causes flattening of the subjacent renal parenchyma.

4. Displacement of capsular arteries. The capsular arteries may be displaced externally in either condition. Examples of conspicuous arcuate displacements and stretching of the capsular artery system in cases of both subcapsular and perirenal hematomas and abscesses have been amply documented in the literature. Rather, I have noted that the level of displacement of the capsular arterial arcade is the angiographic key to the differential text continues on page 438

NephrotomogramNephrotomogramSubcapsular Perinephric Hematoma

Fig. 8—161. Multiple perirenal abscesses.

(a) Plain film shows a large mass in relationship to the lower pole of the left kidney. Displaced renal fascia is seen as a striplike density (arrows) lateral to the upper pole.

(b) Nephrotomogram demonstrates perirenal mass displacing the renal fascia (solid arrows) and flattening the renal margin. In its upper portion, the displaced renal fascia approaches the renal contour (upper arrows). The thickened lateral wall of the perirenal mass itself is seen (open arrows). Another nonopaque mass compresses the upper pole medially.

(c) Gross specimen. Three large perirenal abscesses (A) compress the kidney (K) and displace the thickened renal fascia (arrowheads). Displacement is maximal over the largest abscess but the fascia can be seen to be deflected laterally at some distance from this. This feature is clearly demonstrated radiologically.

(Reproduced from Meyers et al.11)

Subcapsular Renal ThickneingSubcapsular Renal Thickneing
b
Renal Dynamic Image

Fig. 8—162. Perirenal abscess communicating with infected renal cysts.

(a) Intravenous urogram. Mass impressions on lateral minor calyces of the upper pole are secondary to renal cysts. In addition, the renal fascia is seen as a striplike density (arrowheads) lateral to the lower pole.

(b and c) Renal arteriogram. Arterial and nephrogram phases reveal multiple cysts within the left kidney. They appear most confluent within the lower pole where the margin is disrupted. Here the thickened fascia (arrowheads) is displaced laterally. While the superior capsular artery is in close apposition to the upper margin of the kidney, it is displaced outward as it approaches the midportion (upper arrowheads). Some flattening and compression of the renal parenchyma is present at this site. At surgery, pus was immediately apparent when the renal fascia was opened. There was considerable adherence of the renal fascia and perirenal fat to the kidney. Multiple loculations ofpus were found in the perirenal fat. These originated from at least three infected renal cysts. These cysts measured 2-3 cm in diameter, were on the surface of the kidney, and contained thick pus. The perirenal abscesses were drained. (Reproduced from Meyers et al.11)

Perinephric Hematoma

Fig. 8—163. Perirenal hemorrhage secondary to occult renal tumor.

(a) Intravenous urogram. Renal fascia is seen as a striplike density (arrows) displaced laterally by a large mass. This also results in loss of definition of the lateral and inferior borders of the kidney.

(b) Renal arteriogram. Perforating capsular arteries extend through the mass to its lateral limit by the displaced renal fascia (arrows). No definite abnormal intrarenal vasculature is identified.

(c) At surgery, a large collection of blood distended the perirenal space, contained within the cone of renal fascia. Nephrectomy was performed and the pathologic examination disclosed a 3 x 5 x 4 cm infiltrating papillary adenocarcinoma of the lower renal pole.

(d) Bivalved specimen. Extension through the renal capsule had resulted in gross perirenal hemorrhage within the thickened cone of renal fascia.

(Reproduced from Meyers et al.11)

Fig. 8—163. Perirenal hemorrhage secondary to occult renal tumor.

(a) Intravenous urogram. Renal fascia is seen as a striplike density (arrows) displaced laterally by a large mass. This also results in loss of definition of the lateral and inferior borders of the kidney.

(b) Renal arteriogram. Perforating capsular arteries extend through the mass to its lateral limit by the displaced renal fascia (arrows). No definite abnormal intrarenal vasculature is identified.

(c) At surgery, a large collection of blood distended the perirenal space, contained within the cone of renal fascia. Nephrectomy was performed and the pathologic examination disclosed a 3 x 5 x 4 cm infiltrating papillary adenocarcinoma of the lower renal pole.

(d) Bivalved specimen. Extension through the renal capsule had resulted in gross perirenal hemorrhage within the thickened cone of renal fascia.

(Reproduced from Meyers et al.11)

Intrarenal Capsule

Fig. 8—164. Subcapsular abscess.

On the right, the calyces are displaced by a large, relatively lucent mass in the lower half of the kidney. The renal capsule (arrows) is displaced superiorly by a prominent collection that also results in mild compression of the underlying renal margin. The apparent enlargement of the right kidney is secondary to magnification since the kidney is also pushed forward. Decreased function is evident.

At surgery, a large subcapsular abscess containing creamy white pus and some old blood clot was found. The abscess had clearly dissected the capsule off the kidney. It communicated with a large infected thick-walled intrarenal cyst through a small tract along the lateral border of the kidney. It was evident that the cyst accounted for the calyceal deformity and the subcapsular collection also posterior to the kidney accounted for the renal magnification. Drainage and excision of both were accomplished. (Reproduced from Meyers et al.11)

Fig. 8—164. Subcapsular abscess.

On the right, the calyces are displaced by a large, relatively lucent mass in the lower half of the kidney. The renal capsule (arrows) is displaced superiorly by a prominent collection that also results in mild compression of the underlying renal margin. The apparent enlargement of the right kidney is secondary to magnification since the kidney is also pushed forward. Decreased function is evident.

At surgery, a large subcapsular abscess containing creamy white pus and some old blood clot was found. The abscess had clearly dissected the capsule off the kidney. It communicated with a large infected thick-walled intrarenal cyst through a small tract along the lateral border of the kidney. It was evident that the cyst accounted for the calyceal deformity and the subcapsular collection also posterior to the kidney accounted for the renal magnification. Drainage and excision of both were accomplished. (Reproduced from Meyers et al.11)

Subcapsular Hematoma Kidney

Fig. 8-165. Subcapsular hematoma resulting in hypertension ("Page kidney").

(a) Intravenous urogram. The right kidney is displaced medially. Dilatation of the collecting system and ureter is present.

(b) Nephrotomogram demonstrates the displaced and thickened renal capsule (arrowheads) confining a nonopaque mass that is compressing the lateral contour of the kidney.

Illustration continued on opposite page

Fig. 8-165. Subcapsular hematoma resulting in hypertension ("Page kidney").

(a) Intravenous urogram. The right kidney is displaced medially. Dilatation of the collecting system and ureter is present.

(b) Nephrotomogram demonstrates the displaced and thickened renal capsule (arrowheads) confining a nonopaque mass that is compressing the lateral contour of the kidney.

Illustration continued on opposite page diagnosis. If the vessel conforms closely to the border of the mass, a subcapsular collection is indicated (Fig. 8-165c). If deviation of the capsular artery begins at some distance from the extrarenal mass, a perirenal collection is indicated (Fig. 8-162b).

As a differential point, it must be recognized that the capsular arteries will be separated from the cortical margin in cases of renal atrophy.211 Perirenal adipose replacement in instances of acquired shrinkage of the kidney tends to increase the distance between the capsular artery and the atrophied kidney. This separation can be distinguished easily from a subcapsular or perirenal mass displacing the capsular artery.

The marked increase in intrarenal vascular resistance produced particularly by a large subcapsular hematoma may result in striking slowing of arterial flow with failure of opacification of the small intrarenal and capsular ves-sels.184

5. Structure and function of the renal collecting system. Distortion of the calyces and renal pelvis may accompany any gross displacement of the kidney itself. Since peri-renal abscesses result from a site of renal infection that has perforated through the capsule, chronic inflammatory changes involving the calyces may be evident. An intrarenal abscess or hematoma may produce mass displacement upon the collecting system. Failure of excretion of contrast medium on the involved side ("unilateral anuria") can result from the compression of either a perirenal or subcapsular hematoma.212

Computed tomography provides a rapid, noninva-sive, and highly accurate method to evaluate and distinguish the presence of subcapsular and perirenal bleeding. 7,213-217 By virtue of its ability to discriminate very small differences in tissue density, CT confirms and readily makes apparent the characteristic anatomic features permitting localization of the collections (Figs. 8167 through 8-172). Magnetic resonance imaging may also be useful. (Fig. 8-173).

Bridging Renal Septa. The distribution ofperirenal fluid may be limited by the bridging renal septa. Compart-mentalization of a fluid collection by this internal architecture of the perirenal fat, particularly the posterior

Hematoma Subcapsular Renal

Fig. 8—165. Subcapsular hematoma resulting in hypertension ("Page kidney"). Continued.

(c) Renal arteriogram, arterial phase. The avascular mass compresses the renal parenchyma and vessels, producing a pronounced concave lateral border to the kidney, and displaces the superior capsular artery.

(d) Renal arteriogram, nephrogram phase. The renal capsule (arrowheads) is displaced to the same extent as the capsular artery. The renal parenchyma, while markedly compressed, appears intrinsically intact.

At surgery, a large subcapsular hematoma was confirmed, and deep pyelonephritic scars were evident on the surface of the kidney. A right nephrectomy was performed. Pathologic examination confirmed a large, partially organized subcapsular hematoma. A thickened capsule measuring up to 8 mm was present. A 1.2cm resolving abscess in the midportion of the kidney communicated with the hematoma. Hydronephrosis and generalized pyelonephritis were present. Blood pressure returned to normal after operation. (Reproduced from Meyers et al.11)

Fig. 8—165. Subcapsular hematoma resulting in hypertension ("Page kidney"). Continued.

(c) Renal arteriogram, arterial phase. The avascular mass compresses the renal parenchyma and vessels, producing a pronounced concave lateral border to the kidney, and displaces the superior capsular artery.

(d) Renal arteriogram, nephrogram phase. The renal capsule (arrowheads) is displaced to the same extent as the capsular artery. The renal parenchyma, while markedly compressed, appears intrinsically intact.

At surgery, a large subcapsular hematoma was confirmed, and deep pyelonephritic scars were evident on the surface of the kidney. A right nephrectomy was performed. Pathologic examination confirmed a large, partially organized subcapsular hematoma. A thickened capsule measuring up to 8 mm was present. A 1.2cm resolving abscess in the midportion of the kidney communicated with the hematoma. Hydronephrosis and generalized pyelonephritis were present. Blood pressure returned to normal after operation. (Reproduced from Meyers et al.11)

renorenal bridging septum, may mimic a subcapsular collection60 (Figs. 8-174 and 8-175). At times, on CT, a black line separating the renal parenchyma from the hematoma may be seen (Fig. 8-176a), initially described as representing the swollen renal capsule but probably due to a CT boundary artifact.219 I have observed two further differential features in that fluid may further extend within continuous branching septa (Figs. 4-176 and 4-177) and the collection may taper to a beak-shape along one contour at the site of traction by an attached septum (Fig. 8-176). This illustrates that the septa may serve to decompress rapidly accumulating collections.

Treatment. These observations on the localization of subcapsular and perirenal collections are ofconsiderable

help in planning the most appropriate therapy. Whether the underlying cause is predominandy unilat eral kidney disease or a systemic condition involving both kidneys must be considered.224 With the recognition that most extrarenal abscesses are secondary to an infection of the kidney, conservative treatment perhaps with surgical drainage or nephrectomy is determined by the extent ofinvolvement. Percutaneous drainage is being currently recommended as the therapeutic procedure of choice for perirenal abscesses.220 For small lesions, catheter placement is best accomplished under image guidance. A trochar technique can be used in large collection; if no critical anatomy intervenes.221 Separate drains may be required for multifocal or mul-tiloculated lesions. Percutaneous drainage is frequently curative.221,223 About one third of perirenal abscesses show communication with the urinary collecting system;

text continues on page 444

Perinephric Hematoma

Fig. 8-166. Subcapsular and perirenal hematomas secondary to overanticoagulation.

(a) Plain film. Two discrete curvilinear densities are seen external to an apparently enlarged renal silhouette. These represent displaced renal capsule (inner arrows) and renal fascia (outer arrows).

(b) Renal arteriogram. The kidney itself is not enlarged but rather is compressed by a prominent subcapsular hematoma. Blood in the perirenal space also displaces the renal fascia.

Fig. 8-166. Subcapsular and perirenal hematomas secondary to overanticoagulation.

(a) Plain film. Two discrete curvilinear densities are seen external to an apparently enlarged renal silhouette. These represent displaced renal capsule (inner arrows) and renal fascia (outer arrows).

(b) Renal arteriogram. The kidney itself is not enlarged but rather is compressed by a prominent subcapsular hematoma. Blood in the perirenal space also displaces the renal fascia.

Perirenal Hematoma

Fig. 8-167. Perirenal hemorrhage.

Following repair of a thoracoabdominal aortic aneurysm, noncontrast CT demonstrates a prominent acute hematoma (H) shown by high attenuation fluid, which collects in the posterior and lateral aspects of the left perirenal space. The kidney (K) is displaced anteriorly and medially. A small acute subcapsular hematoma is present medially (arrow). (Courtesy of Jay P. Heiken, M.D., Mallinckrodt Institute of Radiology, St. Louis, MO.)

Fig. 8-167. Perirenal hemorrhage.

Following repair of a thoracoabdominal aortic aneurysm, noncontrast CT demonstrates a prominent acute hematoma (H) shown by high attenuation fluid, which collects in the posterior and lateral aspects of the left perirenal space. The kidney (K) is displaced anteriorly and medially. A small acute subcapsular hematoma is present medially (arrow). (Courtesy of Jay P. Heiken, M.D., Mallinckrodt Institute of Radiology, St. Louis, MO.)

Fig. 8—168. Perirenal hemorrhage secondary to renal angiomyolipoma.

(a) CT scan after intravenous contrast medium demonstrates active bleeding (arrows) into hemorrhagic collection within right perirenal space.

(b) At a lower level, blood distends the perirenal space. A structure of low attenuation density (arrow) corresponds to a defect in the nephrogram. This represents the fatty nature of the parenchymal tumor from which bleeding has occurred.

(c) Selective right renal arteriogram demonstrates active bleeding (arrow) into the perirenal space from vessels associated with the tumor mass. (Courtesy of Daniel Wise, M.D., Toronto Western Hospital, Toronto, Canada.)

Perirenal Hematoma ScanBridging Septa

Fig. 8—169. Compartmentalization of perirenal blood by bridging renal septa.

This 78-year-old man, receiving Coumadin therapy for cardiac problems, fell and developed left flank pain and discoloration.

(a and b) Multiple sites of acute perirenal hemorrhage (H), secondary to unsuspected bleeding angiomyolipoma (asterisk) of the left kidney (K), are loculated by bridging renal septa. The left kidney is displaced. Bleeding into the flank wall and a segment of the posterior pararenal fat from the fall is also noted. (Courtesy of Gary Ghahremani, M.D., Evanston Hospital, Evanston, IL.)

Fig. 8—169. Compartmentalization of perirenal blood by bridging renal septa.

This 78-year-old man, receiving Coumadin therapy for cardiac problems, fell and developed left flank pain and discoloration.

(a and b) Multiple sites of acute perirenal hemorrhage (H), secondary to unsuspected bleeding angiomyolipoma (asterisk) of the left kidney (K), are loculated by bridging renal septa. The left kidney is displaced. Bleeding into the flank wall and a segment of the posterior pararenal fat from the fall is also noted. (Courtesy of Gary Ghahremani, M.D., Evanston Hospital, Evanston, IL.)

Perirenal Hematoma Scan

Fig. 8—170. Intrarenal rupture of abdominal aortic aneurysm.

Enhanced CT scan shows a low-density tubular mass extending from the aorta directly into the left renal hilus. This originated from a localized aortic aneurysm that ruptured along the renal vascular pedicle. The posterior perirenal and pararenal spaces are intact. This case indicates that the renal vascular pedicle may provide an avenue for dissection of blood into the perirenal space. (Reproduced from Gavant et al.218)

Perirenal Pararenal Fat

Fig. 8—171. Subcapsular hematoma.

CT demonstrates that a tense collection of blood has stripped the renal capsule, which is thickened and enhanced. The perirenal fat and Gerota's fascia are maintained.

Gerota Fascia Bleeding

Fig. 8—172. Subcapsular and perirenal hemorrhage secondary to renal cell carcinoma.

CT demonstrates a high attenuation Subcapsular hematoma (arrows) and bleeding gravitating to the posterior contour of the perirenal space (arrowhead). The enlarged left renal vein is tumor-filled.

(Reproduced from Zagoria et al. )

Fig. 8—172. Subcapsular and perirenal hemorrhage secondary to renal cell carcinoma.

CT demonstrates a high attenuation Subcapsular hematoma (arrows) and bleeding gravitating to the posterior contour of the perirenal space (arrowhead). The enlarged left renal vein is tumor-filled.

(Reproduced from Zagoria et al. )

Fig. 8—173. Perirenal hematoma.

MRI demonstrates perirenal hemorrhage (H) that has loculated medially and inferiorly. It is discretely confined by the thickened perirenal fascia. The kidney (K) is displaced anteriorly, laterally and superiorly.

(a) T1-weighted coronal view.

(b) T2-weighted axial view.

(Courtesy of Jay P. Heiken, M.D., Mallinckrodt Institute of Radiology, St. Louis, MO.)

Perinephric HematomaPerinephric Hematoma

Fig. 8—174. The bridging dorsal renorenal septum.

Acute perirenal bleeding tracking along the bridging renal septa outlines clearly the dorsal renorenal septum (arrows). Loculation of blood deep to this can simulate a subcapsular renal hematoma.

successful treatment requires concurrent drainage of the collecting system of it is obstructed.225 In subcapsular or perirenal hematoma in the presence of a renal tumor, hydronephrosis, renal artery aneurysm, lithiasis, or unilateral renal tuberculosis, nephrectomy does not present any significant long-term problem. On the other hand, if the etiology is nephritis, arteriosclerosis, periarteritis nodosa, or a blood dyscrasia and nephrectomy must be performed as a life-saving procedure, careful follow-up observation of the remaining kidney must be maintained. If the hematoma is not large and adequate visualization of the bleeding site can be obtained, so that it can be controlled with sutures, a biopsy of the involved renal tissue may be preferable to nephrectomy.

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  • AULIS
    Is a perirenal subcapsular hematoma dangerous?
    3 years ago
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    What are perirenal bands made of?
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