(Objective) To evaluate the clinical usefulness of the classification for renal injury, proposed by Japanese Association for the Surgery of Trauma (JAST). (Method) JAST classification for renal injuries consists of categories as: Type I (subcapsular injury); Type II (superficial injury); type III (deep injury); type IV (pedicle injury). Type III injuries are subclassified into: IIIa (deep laceration); IIIb (transection); IIIc (fragmentation). Type IV are subclassified as: IVa (M), IVa (S) (the occlusion of main or segmental renal artery); IVb (renal vessels laceration). Each of the degrees of severity in hemorrhage (H factor) and extravasation of urine (U factor) should be appended as: H0, U0 (not recognized); H1, U1 (remaining within perinephric space); H2, U2 (extending through Gerota's fascia); H3, U3 (extending to contralateral side). We examined the initial management and overall outcome of blunt renal injuries recorded at our institute. All patients were classified according to the JAST criteria. Statistical analyses were applied to find the correlations between type and H factor, and between type and U factor. We also determined which parameter (type, H or U) is the most significant factor responsible for the outcome of treatment in the injured kidney. (Result) One hundred and fifteen consecutive cases of blunt renal injuries from 1982 to 1999 were investigated. Significant correlations were observed between type (I-IIIc) and H factor, and also between type (IIIa-IIIc) and U factor. Twenty-nine patients (25%) underwent immediate surgical exploration; 1 (2%) in type I or II or IVa (S), 5 (18%) in IIIa, 4 (50%) in IIIb, 7 (100%) in IIIc and 12 (100%) in IVa (M) or IVb. Among the 86 conservatively-managed patients, TAE or surgical intervention was required later in six patients. Nineteen (17%) patients were nephrectomized. The renal loss rates were 0% in type I or II or IVa (S), 7% in IIIa, 25% in IIIb, 57% in IIIc and 92% in IVa (M) or IVb, respectively. The differences of severities of the type and the H factor are statistically significant between the groups of injured kidney preserved and lost. Logistic regression analysis suggested that the type was an independent factor predicting outcomes of injured kidneys. (Conclusion) It seemed that the type category is most useful when managing patients with renal injuries and also evaluating outcomes of them.
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