Renal Trauma

Fig. 7.1

Baseline US examination (a) is inadequate to detect renal laceration because it is slightly hypo-isoechoic to the surrounding parenchyma. Color Doppler (b) shows a relative homogeneous perfusion. After contrast injection, CEUS demonstrates a large filling defect due to deep parenchymal laceration (c, d)

In addition, CEUS exceeded the limits of the B-mode US and the US color and power Doppler and expanded the applications of the method especially in abdominal trauma in children.

The main limit of CEUS in kidney traumatic lesions is the impossibility to visualize pelvicalyceal and ureter injuries, since contrast agents are not concentrated in the collecting system. In these cases, CE-MDCT should be always performed in CEUS-positive patients to exclude active bleeding and urinomas.

7.3 Classification

Several classifications have been defined for the assessment of the type of renal injury, but the classification proposed by the Committee on Organ Injury Scaling of the American Association for the Surgery of Trauma (AAST) is now widely accepted as the grading scale, which also ensures a common consensus between surgeons and radiologists for proper management of renal injuries. The current AAST grading system is based on surgical findings, which can be diagnosed by MDCT [7]:

I – Renal contusion or subcapsular hematoma with intact capsule
II – Superficial cortex laceration (<1 cm) that does not extend to deep medulla or collecting system or nonexpanding hematoma
III – Deep laceration(s) (>1 cm) without urine extravasation
IV – Laceration(s) extending into collecting system with contained urine leak, main renal artery or vein injury with contained hemorrhage, segmental parenchymal infarction
V – Shattered renal parenchyma, renal vascular pedicle avulsion, or devitalized kidney

7.3.1 Grade 1

Intrarenal hematomas (or contusions) are not easily detectable on B-mode evaluation. Contusions usually appear as ill-defined, round, or ovoid hyperechoic areas within the renal parenchyma. They constitute 75–85 % of all renal injuries [8]. The treatment is conservative and the lesion tends to resolve within 1 or 2 weeks.

Subcapsular hematomas appear as round or elliptic inhomogeneous hyper- and hypoechoic fluid collection along the renal contour, under the renal capsule. If the hematoma is large in size, it may cause flattening or depression of the underlying renal surface and compress the parenchyma (Fig. 7.2).

Fig. 7.2

Grade 1: subcapsular hematoma. Conventional US shows an elliptic inhomogeneous hypoechoic collection along the renal contour, which flattens the renal surface. CT confirms the presence of large subcapsular hyperdense hematoma, confined under the renal capsule. The attenuation values are between 45 and 90 HU

7.3.2 Grade 2

Subsegmental infarcts or minor lacerations (<1 cm) may appear as defects in the periphery of the renal parenchyma without involvement of the collecting system. CEUS has a limited sensitivity in the detection of these lesions, while CE-MDCT can demonstrate small, sharply demarcated, wedge-shaped areas of decreased contrast enhancement, due to stretching and thrombotic occlusion of small accessory renal artery, capsular artery, or intrarenal subsegmental branch. The treatment is conservative and subsegmental infarction results in cortical small incisure.

Perinephric hematomas appear as semilunar inhomogeneous hyper- and hypoechoic fluid collection near the kidney (Fig. 7.3). These are differentiated from subcapsular hematomas because perinephric hematomas are confined between the renal parenchyma and Gerota’s fascia, outlining the renal contour extending over a wider area without producing flattening or depression of renal margins, and occur following a laceration of the renal capsule.

Fig. 7.3

Grade 4: major laceration (>1 cm) involving the collecting system. Both CEUS and CE-MDCT show deep wedge-shaped areas of decreased contrast enhancement. The deepest laceration also involves the pelvis with extensive anechoic fluid perinephric collection, confined into the Gerota’s fascia

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