Renal Transplant Imaging and Intervention:
Practical Aspects - 5

Charles V. Zwirewich, MD

Lymphocele

Lymphoceles are the most common fluid collections in the transplant population, occurring in 5-15% of patients, and are the collections most frequently associated with ureteral obstruction [32,40,41]. Most develop within one year of transplantation. Risk factors include incomplete ligation of the pelvic lymphatics or a prior episode of severe rejection [41]. These patients may present with a clinically palpable mass, leg pain and oedema, and impaired graft function due to compression of the ureter [32]. Diagnosis can be confirmed by needle aspiration which shows a creatinine level equivalent to serum. On ultrasound, these collections may be heavily septated and large, but usually grow slowly (Fig 25).

Fig 25 Figure 25. A large septated lymphocoele (arrows) is situated between the lower pole of the transplant (k) and the bladder (b).

The majority of lymphoceles are asymptomatic, requiring no therapy [41]. Treatment options for symptomatic noninfected lymphocoeles include open surgical drainage, percutaneous aspiration with or without injection of a sclerosing agent and laparoscopic marsupialization [41,42]. Percutaneous drainage is useful to alleviate obstruction prior to marsupialization. Infected lymphoceles should be drained percutaneously and usually require no additional therapy (Fig 26) [41].

Fig 26a Figure 26a. Ultrasound guided percutaneous lymphocoele drainage. The patient had previously undergone attempted laparoscopic marsupalisation of the large unilocular lymphocoele (ly) adjacent to the transplant (k). The surgeon could not find the collection.

Fig 26b Figure 26b. A 22G spinal needle (arrow) was advanced into the collection under US guidance. Using a tandem approach, a 6.7 Fr McGahan catheter was advanced and coiled in the lymphocoele cavity. After 24 hours of drainage, the lymphocoele cavity was filled with methylene blue, allowing the surgeon to easily identify the collection at laparoscopy.

Procedure Related Complications

Haemorrhage

The complication rate for percutaneous biopsy of the renal graft is approximately 5-8%. Perinephric hematomas account for 25-30% of all complications. While most are small and do not require additional therapy, haematomas may occasionally compress the ureter and produce hydronephrosis. Containment of an acute or enlarging haematoma within the renal capsule (Fig 27) or adjacent tissues may compress the renal parenchyma sufficiently to impair function, but rarely results in hypertension (the "page kidney" phenomenon).

Fig 27 Figure 27. Subcapsular haematoma following percutaneous biopsy (*).

Arteriovenous Fistula (AVF)

An AVF occurs as a consequence of simultaneous laceration of a renal artery branch and an adjacent vein during biopsy. These occur in up to 18% of biopsied kidneys but are almost always small and asymptomatic. Observation is generally all that is necessary as most spontaneously thrombose. Embolization is reserved for the 1-2% of fistulae associated with hemodynamically significant AV shunting or recurrent hematuria.

CDI features of AV fistulae include:

Focal colour aliasing within the nidus
Perivascular colour assignment at low flow velocity settings due to tissue vibration artifact [13].

The hallmarks of AV fistulae on PD include low resistance, high velocity arterial flow within the feeding artery and high velocity arterialized venous flow in the associated draining vein (Fig 28).

Figure 28. Arteriovenous fistula following transplant biopsy. Perivascular, mosaic colour assignment due to tissue vibration is visible immediately deep to the nidus (arrow, 28a) at a low colour doppler velocity scale setting. At a higher velocity scale (28b) the feeding artery and vein (v) can be distinguished. PD demonstrates high velocity, low resistance arterial (28c) and pulsatile venous flow (28d), characteristic of AV shunting.

Fig 28a Figure 28a. Mosaic colour asignment (arrow) due to arteriovenous fistula (AVF).

Fig 28b Figure 28b. Feeding artery (a) and vein (v) seen entering/leaving the nidus of an AVF (arrow).

Fig 28c Figure 28c. High velocity, low resistance flow due to AVF.

Fig 28d Figure 28d. Pulsatile venous flow due to AVF.

Pseudoaneurysm

Pseudoaneurysms are rare and may occur as a consequence of renal biopsy, infection within the graft or dehiscence of the arterial anastomosis [12]. Any cystic area which develops in or adjacent to the graft on serial ultrasound studies should be interrogated with doppler to exclude the presence of pseudoaneurysm [22]. CDI shows a high velocity jet from the feeding artery with eddying of blood referred to as the Yin-Yang sign within the aneurysm cavity (Fig 29).

Fig 29a Figure 29a. Colour doppler of pseudoaneurysm. A high velocity jet from the feeding artery enters the aneurysm sac during systole.

Fig 29b Figure 29b. In a different patient, CDI shows the eddying of blood within the sac during diastole ("Yin-Yang" sign).

PD shows the jet, turbulent flow within the cavity and the classic biphasic flow pattern at the pseudoaneurysm neck (Fig 30). While most regress spontaneously [12], treatment of symptomatic lesions is by embolization or surgical repair depending on location.

Fig 30 Figure 30. Biphasic flow at the neck of a pseudoaneurysm.

And Finally: List of References

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Dr C V Zwirewich
Vancouver Hospital & Health Sciences Centre
Vancouver, B.C.
zwirecv@unixg.ubc.ca