The central approach of renal transplant ultrasound is to evaluate for possibly treatable surgical or medical complications arising in the transplanted kidney.
Institutions vary in the exact schedule of renal transplant ultrasound assessment, but it is common to obtain an initial ultrasound 24-48 hours post-transplant, often performed with a radionuclide imaging (e.g. iodine-131 orthoiodohippurate, Tc-99m MAG3).
Knowledge of the surgical technique is important, and reviewing the operation report will often enhance interpretation of the studies. The transplanted kidney is normally placed extraperitoneally in either iliac fossa, most commonly the right.
In cadaveric renal transplants the main renal artery is harvested with an attached portion of donor aorta which is then anastomosed end-to side to the recipient external iliac artery. Live donor transplants involve a direct end-to-side renal arterial graft to the external iliac or an end-to-end anastomosis with the internal iliac artery.
The main renal vein is almost always grafted to the recipient external iliac vein in an end-to-side manner.
Urinary drainage is usually restored by implanting the donor ureter into the bladder dome (ureteroneocystostomy) although it can also be implanted to the native ureter or renal pelvis.
Gross structural assessment is as for a native kidney and includes:
- renal echogenicity
- corticomedullary differentiation should be preserved
- renal size
- enlargement may indicate oedema, which is non-specific, but a change in size between studies is an indication of underlying disease
- proximal hydroureter
The nature of post-transplant fluid collections cannot be reliably determined on ultrasound appearances alone as most are anechoic with variable internal acoustic characteristics. This is best done based on the time scale as different fluid collections tend to present at different times in the postoperative period:
- immediate post-operative: haematoma
- 1-2 weeks post-op: urinoma
- 3-4 weeks post-op: perinephric abscess
- 2nd month and beyond: lymphocoele
renal vein thrombosis or stenosis
- reversal of diastolic flow in the renal artery
- renal artery thrombosis or stenosis
- high flow velocities at the stenosis site 7
- peak systolic velocity ≥2 m/s
- velocity difference between pre- and post-stenotic segments of 2:1
- post stenotic spectral widening
- parvus et tardus waveform distal to stenosis
- normally develops after months or weeks
- high flow velocities at the stenosis site 7
- pseudoaneurysm: usually following biopsy or other renal puncture
- intrarenal arteriovenous fistula
There are a number of medical causes of renal transplant dysfunction or failure 7:
- acute tubular necrosis
- hyperacute: immediately post-operative
- acute: 1-3 weeks post-transplant
- chronic: >3 months post-transplant
- drug nephrotoxicity
- recurrent disease, e.g. recurrent IgA nephropathy
- occurs in 80% of recipients in the first year
Ultrasound findings in medical graft complications are non-specific and can include:
- raised resistive index (RI) > 0.8 7
- focal or diffuse parenchymal oedema
Ultimately, patients with suspected medical causes of transplant dysfunction undergo biopsy for definitive diagnosis.
Ultrasound - renal
- ultrasound (introduction)
- renal ultrasound
- renal stone
- focal lesion
- renal vascular
- renal transplant ultrasound
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