Historical milestones and modern trends
The first successful kidney transplantation was performed in the USA in 1950. Initially, the widespread adoption of this revolutionary technique was severely limited by the absence of effective immunosuppressive therapy in the medical arsenal. A true breakthrough and subsequent surgical success were achieved through operations between identical twins—in such unique clinical cases, immunosuppression was simply not required. Over time, with the advent of potent drugs to control the immune response, cadaveric transplantation became possible.
In modern clinical practice, living-donor transplantation is rapidly gaining popularity. This is directly related to the objectively limited availability of cadaver organs. For example, the share of such procedures reaches nearly 50% in the USA and about 30% in the UK. Among current trends, the active use of complex paired schemes as well as the formation of pooled donor groups stand out. It is important to note that thanks to advances in transplantology, patient incompatibility by blood group (ABO system) is no longer viewed as a contraindication to surgery.
Surgical technique features
The surgical technique for kidney transplantation is not strictly standardized. It varies significantly depending on the operating surgeon's preferences, the recipient's individual vascular anatomy, and the presence of previous grafts in the medical history. The traditional location for the transplanted organ is the right or left fossa iliaca.
The formation of vascular anastomoses has specific strict characteristics:
- Arterial anastomosis: most commonly performed in an end-to-side fashion (end-to-side) with the external or common iliac artery. If the donor kidney has multiple arteries, surgeons may form an anastomosis on a single patch, which is technically feasible exclusively in cadaveric donations.
- Venous anastomosis: is also typically performed using the classic end-to-side technique with the recipient's external iliac vein.
- Ureterovesical anastomosis: exhibits high variability in execution and often incorporates a special antireflux technique. The usual site for this connection is the dome of the urinary bladder. However, if the patient's bladder has an abnormally large capacity, the anastomosis may be located significantly lower than the standard level.
Diagnostic imaging: baseline ultrasound (B-mode)
Ultrasound (US) examination is rightly considered the primary radiological imaging modality for the transplanted kidney. It is used for both short-term monitoring and long-term graft management. The main advantages of the method include high equipment portability, low cost, complete absence of ionizing radiation and nephrotoxicity. Because the allograft is located superficially, physicians can use high-frequency transducers to obtain high-resolution images.
A comprehensive examination requires a skillful combination of standard greyscale B-mode and Doppler ultrasound. In B-mode, the physician must measure the graft length and evaluate for the presence of hydronephrosis, calculi, or focal pathology. Special attention is paid to the perirenal tissues to check for pathological fluid collections.
An integral part of the protocol is the assessment of the urinary bladder for wall thickening, stones, or tumors. This examination is performed before and especially after micturition (particularly in cases of hydronephrosis or infection). The orientation of the kidney on the screen depends on the surgical technique used: the physician must first determine the axial plane in order to correctly obtain true longitudinal sections. The presence of ureteral stents must always be documented in the report.
Doppler ultrasound and resistive index (RI)
Doppler ultrasound (Doppler US) is used routinely. Color and spectral Doppler are employed for a detailed evaluation of intrarenal and extrarenal blood flow. The spectral pattern of the graft artery is similar to that of a native kidney. However, extensive measurements of the Doppler waveform have limited value because they do not allow differentiation between rejection and acute tubular necrosis (ATN).
To objectify the data, the resistive index (Resistive Index, RI) is calculated. The formula is: `RI = (Peak Systolic Velocity - End Diastolic Velocity) / Peak Systolic Velocity`. An RI value greater than 0.8 is considered abnormal. However, the method suffers from a lack of specificity due to the complex interaction between vascular resistance and compliance, making clinical evaluation a crucial part of the diagnosis.
Briefly: answers to topical questions
What causes can lead to an elevated resistive index (RI) of greater than 0.8 in a kidney transplant?
An elevated resistive index (RI) of greater than 0.8 in a renal allograft is considered an abnormal sign and may be caused by Chronic Rejection. In this pathology, the process is insidious and accompanied by a gradual deterioration of organ function. The RI metric itself suffers from a lack of specificity due to the complex interaction between the renal vascular resistance and its compliance. For this reason, clinical evaluation and accompanying sonographic findings remain an essential part of the assessment for accurate diagnosis.
What types of pathological perirenal fluid collections are detected on ultrasound after transplantation?
Ultrasound after transplantation reveals the following types of pathological perirenal and pelvic fluid collections:
- Urinoma (Urinoma) — forms shortly after surgery due to urine leakage.
- Lymphocele (Lymphocele) — occurs at later stages.
- Haematoma (Haematoma) — a collection of blood.
- Seroma (Seroma) — a collection of serous fluid.
These fluid collections can cause external compression of the urinary tract, ultimately leading to graft hydronephrosis.
What types of renal transplant rejection exist depending on the timing of onset?
Depending on the timing of onset, there are three main types of renal transplant rejection:
- Hyperacute rejection — develops within 1–5 days after surgery. The cause is the presence of pre-existing antibodies in the recipient.
- Acute rejection — occurs between 5 and 30 days. The underlying mechanism is cell-mediated immunity activation.
- Chronic rejection (Chronic Rejection) — develops from 3 months to several years (or 6 months and later). The process is accompanied by a gradual deterioration of graft function.
Which vascular complications of a kidney transplant are diagnosed using color Doppler flow imaging?
Color Doppler flow imaging (CDFI) is used to diagnose the following vascular complications of a renal transplant:
- Renal artery thrombosis (Renal Artery Thrombosis) — characterized by a complete absence of blood flow in the main and intrarenal arteries.
- Arteriovenous malformations (Arteriovenous Malformations) — manifested by arterialized venous flow or a focal zone of disorganized blood flow.
- Pseudoaneurysms (Pseudoaneurysm) — an intrarenal lesion that appears as a cyst but demonstrates clear communication with the vascular bed upon examination.
To remember the normal spectral pattern of the artery, keep the "ski slope pattern" metaphor in mind: it is a low-resistance flow where the diastolic velocity is approximately 1/3 of the systolic velocity. Its reduction is a sign of pathology.
Class and exam questions
Why is it possible to transplant multiple arteries as a single block in deceased-donor transplantation?
In such cases, surgeons can form an anastomosis on a single patch, which is technically feasible when procuring an organ from a deceased donor, unlike living donation.
Does ultrasound allow for a reliable distinction between transplant rejection and acute tubular necrosis (ATN)?
No, extensive measurements of the Doppler waveform have extremely limited clinical value for the differential diagnosis of specifically these two conditions.
Where is the ureterovesical anastomosis standardly located?
The usual site of creation is the dome of the urinary bladder. If the bladder has a large capacity, the anastomosis may be placed lower.
What else to study on this topic
- Organization of paired kidney exchange schemes and pooled donor groups.
- Antireflux surgical techniques in ureterovesical anastomosis creation.
- Differential diagnosis of perirenal fluid collections.
- Acute tubular necrosis (ATN) of the transplant: pathogenesis and clinical course.
- Impact of tissue compliance on the resistive index (RI) value.
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