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SonoPhile

Ultrasonography (US) is the first-line imaging modality after kidney transplantation and most often the only one available due to its overall accessibility and the advantage of bedside investigations without need of transportation, sedation, or general anesthesia. After kidney transplantation, complications can be divided into early and late in the clinical course as well as vascular and non-vascular. 

Value of Doppler ultrasonography after pediatric kidney transplantation

a, b Kidney vein stenosis due to a lymphocele with kinking of the transplant vessels

  • Kidney Vein Stenosis:

    • Causes: Tight suturing at anastomosis, compression by kinking or extrarenal fluid collections.

    • B-Mode US: Shows vessel diameter narrowing with proximal dilatation.

    • Color Doppler US: Reveals aliasing artifact.

    • PW Doppler: Indicates increased flow velocity.

  • Kidney Vein Thrombosis:

    • Causes: Surgical complications, size disparity in donor-recipient vessels, ischemia, hypercoagulable states, hypovolemia, venous compression (e.g., hematomas, lymphoceles), severe acute rejection.

    • Grayscale US: Shows increased kidney volume and possibly echogenic material within the vein.

    • Progression: Kidney may become echogenic; initially larger but can shrink over time.

    • Doppler Signs: Absent flow in kidney vein, abnormal wave pattern in kidney artery and segmental arteries (reduced velocity), possible reverse diastolic flow.

    • Partial Thrombosis: High resistive index (> 0.8) in affected segments.

  • Post-Transplant Arterial Hypertension in Children:

    • Common causes: Primary kidney disease, immunosuppressive medication side effects, hormonal disturbances, familial predisposition, kidney artery stenosis.

  • Kidney Artery Stenosis After Transplantation:

    • Prevalence: Estimated 5-30%, varies based on hemodynamic significance criteria and diagnostic methods.

    • Risk factors: Surgical complications (vessel damage, intimal dissection, improper suturing), arteriosclerotic plaques in donor organ, cytomegalovirus infections, delayed graft function.

  • Diagnostic Imaging in Kidney Artery Stenosis:

    • B-Mode US: Checks diameter and possible narrowing (> 60%) of kidney artery.

    • Color Doppler: Shows aliasing artifact at stenosis.

    • PW Doppler: Diagnostic criteria include:

      • Turbulence (spectral broadening).

      • Peak systolic velocity > 200 cm/s (cut-off 180-400 cm/s).

      • Prolonged acceleration time (> 0.1 s).

      • Loss of early systolic peak.

      • High diastolic flow velocity and low resistive index.

a, b Kidney artery stenosis of a kidney graft.

Arteriovenous fistula after kidney biopsy. In the pulse-wave (PW)-Doppler, a turbulent flow pattern with a high flow velocity of > 300 cm/s is depicted

Arteriovenous Fistulas and Pseudoaneurysms in Kidney Transplantation:

  • Etiology: Mostly iatrogenic post-kidney biopsies, often resolve spontaneously.

  • Arteriovenous Fistulas:

    • Occasional cause of steal phenomenon.

    • Grayscale ultrasound shows feeding vessel within transplant.

    • Duplex sonography features:

      • Turbulent flow with aliasing artifact.

      • High flow velocity in feeding artery and draining vein.

      • Low resistive index (RI) due to high diastolic flow.

  • Pseudoaneurysms:

    • Result from vessel wall injury (biopsy, trauma, infection).

    • Grayscale ultrasound appearance:

      • Cyst-like structure.

    • Color imaging shows intense bidirectional flow.

Overall, US is an available and immediate diagnostic tool for the pre- and post-transplantation surveillance of children with a kidney transplant. Major vascular complications such as kidney vessel stenosis or thrombosis can be diagnosed early and with safety. Non-vascular complications such as hydronephrosis, hematoma and lymphocele can be easily assessed.

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Conclusion

Credit to: Franke D. (2022). The diagnostic value of Doppler ultrasonography after pediatric kidney transplantation. Pediatric nephrology (Berlin, Germany), 37(7), 1511–1522. https://doi.org/10.1007/s00467-021-05253-y

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