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PERINEPHRIC COLLECTIONS

  • It is not infrequent for kidney transplants to have one or more small perinephric collections in the immediate postoperative period

  • Most such collections are small and represent expected sequel of the surgical procedure (i.e., serous or hemorrhagic)

  • The clinical relevance of perinephric collections is associated with their:

    • Size

    • Location

    • Etiology

    • Growth

    • Physiologic relevance

  • Collections associated with kidney transplantation include but are not limited to:

    • Seromas

    • Hematomas

    • Urinomas

    • Lymphoceles

    • Abscesses

  • Because some collections may potentially enlarge and result in functional impairment of the graft, baseline examinations should document their size, location, and extension as a reference for future comparisons

  • Although ultrasound (US) is very sensitive in the detection of fluid collections, the sonographic appearance of the collections can be nonspecific

  • A combination of imaging modalities, chronology relative to the surgery, clinical findings, and laboratory information may assist in suggesting a possible etiology

  • Imaging studies, particularly ultrasound, may guide diagnostic and therapeutic drainage procedures

SEROMAS

  • The presence of small pockets of serous fluid collections after the transplant surgery is almost an expected finding

  • They are usually small, crescent-shaped, well-defined collections of anechoic fluid with no mass effect

  • They usually reabsorb progressively

  • Seromas are characterized by water attenuation on computed tomography (CT) and water signal intensity on magnetic resonance imaging (MRI) (Figure 94-1)

FIGURE 94-1

Ultrasound in the immediate postoperative period showing a collection (arrow) surrounding the posterior aspect of the lower pole of the graft. Such small collections, in the absence of clinical symptoms and no sequential increases in size, can be followed conservatively with serial imaging.

HEMATOMAS

  • Blood collections are common postoperatively, but may also result from biopsies, trauma, or spontaneous bleeds

  • Hematomas may be subcapsular or extracapsular within the extraperitoneal space

  • In the peritoneal space, blood tends to accumulate following the classic patterns of fluid migration within the peritoneal cavity

  • Hematomas may also be intraparenchymal and potentially be confused with other masses

  • The imaging appearance of hematomas is variable and depends on their stage of evolution

Intraparenchymal Hematoma (Figures 94-2 and 94-3)

  • In the acute phase hematomas are echogenic on ultrasound

  • In later phases, they tend to be hypoechoic, heterogenous and often septated with progressive decrease in size

  • Their main feature on CT imaging is hyperattenuation, although with time the attenuation decreases and mixed-density collections with occasional fluid–fluid levels may be seen (“hematocrit effect”)

  • Although on MRI hematomas can have a variable appearance based on their stage of iron oxidation, they typically show hyperintensity on both T1 and T2 (methemoglobin)

FIGURE 94-2

Longitudinal and transverse sonograms show an ovoid mass (arrows) with a central echogenic component and an outer hypoechoic rim located in the posterior region of the graft indenting on the sinus. Although this finding initially ...

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