ultrasound guided renal biopsy

Percutaneous renal biopsy, utilizing either ultrasound or CT, allows for an accurate, reliable method of acquiring renal tissue for histopathological assessment.

The biopsy may be of a native or transplant kidney. It is divided into two types:

• non-focal or non-targeted
• focal or targeted (i.e. directed at a lesion)

Either type may be performed as a CT-guided biopsy or as an ultrasound-guided biopsy . Recent description has been given of the use of 3D cone beam CT in assisting the biopsy of particularly challenging focal lesions .

This depends on both patient and operator factors, such as patient body habitus, ability to cooperate and operator experience. Transplant renal biopsy is usually undertaken with ultrasound guidance given its more superficial location in the pelvis.

An alternative option for percutaneous CT/US guidance is the transjugular renal biopsy.

Indications

• focal lesion non-characterized on diagnostic imaging
• renal failure with unknown cause (typically a nephropathy)
• deteriorating renal function in a transplant patient

For focal mass lesions, the established indications include:

• known extra-renal malignancy
• suspected renal lymphoma
• prior to ablation therapy
• multiple or bilateral renal masses
• diagnostic dilemma of infection/malignant mass

Contraindications

The contraindications must be considered individually in each case. Overall, the most important contraindications are:

• uncooperative patient
• uncorrectable bleeding diathesis (abnormal coagulation indices)

Procedure

Laboratory parameters for a safe procedure

Interventional procedures like renal biopsy require special attention to coagulation indices. There are widely divergent opinions about the safe values of these indices for percutaneous biopsies. The values suggested below were considered based on literature review, whose references are cited below:

• complete (full) blood count:
  • platelet > 50000/mm3  (some institutions determine other values between 50000-100000/mm)
• coagulation profile:
  • some studies showed that having a normal INR or prothrombin time is no reassurance that the patient will not bleed after the procedure:
    • international normalized ratio (INR) ≤ 1.5
    • normal prothrombin time (PT)/partial thromboplastin time (PTT)

Pre-procedure preparation

• written informed consent
• assessment of patient's cooperation for the procedure

Equipment

• single or co-axial needle set: usually an 18 G core biopsy needle
• 1% lidocaine/lignocaine
• midazolam (for sedation): select cases only; assess on a case-by-case basis
• histopathology department pots

Technique

Focal biopsies usually require only a single core. Non-focal biopsies typically require two cores. This influences technique as the latter requires a co-axial needle set.

For native or transplant non-focal kidney biopsies, the core is usually taken from the lower pole.

Both ultrasound and CT biopsies are normally performed with the patient prone or on occasion on the ipsilateral side up position in CT. Transplant biopsies are performed supine due to the superficial position in the pelvis.

CT guidance is preferred for those of larger body habitus. Operator preference plays a part too.

After the procedure, a brief assessment for perinephric or intraparenchymal hemorrhage is advised.

Post-procedure care

Bed-rest is advised as well as regular observations for 4 hours (pulse, blood pressure, SpO2) and active questioning of the patient of any pain or hematuria.

The observation period should allow an ample opportunity to identify and treat a potential complication in a timely manner to prevent a serious or catastrophic outcome, this varies with each institution's protocol. One large experience review major complications were identified in >90% of cases by 24 hours .

Complications

Percutaneous renal biopsy remains a safe procedure, but the risk of complication is higher in patients with advanced renal insufficiency . Some studies have also shown that hypertension and amyloidosis has a significant influence on the complications . These patients may benefit from a longer observation period.

Complications include:

• perinephric (retroperitoneal) or intra-renal hematoma
• hematuria
• arteriovenous fistula or pseudoaneurysm
• colonic injury (very rare with image guidance)
• pneumothorax (very rare with image guidance)

Histopathology

Tissue sample adequacy

Adequacy depends on the disease in question.

In diseases with focal changes (e.g. focal and segmental glomerulosclerosis), at least 10 glomeruli would be optimal.

Even diseases with diffuse changes (e.g. membranous glomerulonephritis), show variation in terms of severity, therefore at least 5-10 glomeruli required to properly assess the extent and severity of the disease. At least two biopsy cores with a diameter of at least 1.2 mm are recommended.

Histopathological analysis

Core 1

Fixed in paraffin then used for the following staining procedures for light microscopy:

A: Routine stains:

• Hematoxylin and eosin (H&E)
• Periodic acid-Schiff’s (PAS)
• Fibrous tissue stain (e.g.elastic van Gieson etc)
• Silver stain

B: Optional stains:

• Kossa stain (calcifications)
• Congo red stain (amyloid)

C: Immunohistochemistry: IgG, IgA, IgM, C3, C1q

Core 2

Used for immunofluorescence studies (frozen sections), electron microscopy (fixed in glutaraldehyde) and additional tests.

Not every biopsy requires electron microscopy. Some conditions (e.g. Alport’s disease; immunotactoid disease; minimal change nephropathy) require electron microscopy for a definite diagnosis.