Renal diseases and failure are often difficult to evaluate in term of prognosis and disease development due to the particular aspect of the evolution of renal insult that becomes an autonomous disease by itself, in spite of the original cause that started the problem (e.g., UTI, vascular shock, infectious diseases, etc.) Detection of generalized renal diseases which are potentially reversible may justify for a guarded to positive prognosis and vigorous employment of specific techniques, also expensive, such is the hemodialysis. Whereas the detection of generalized irreversible renal damage may not warrant the same effort and expenses in treatment. Renal function tests do not provide enough reliable information concerning the underlying renal disease or the possibility to recovery for the renal diseases itself. Renal biopsy is indicated to confirm, support or eliminate diagnostic hypothesis based on history, physical examination, laboratory test and diagnostic imaging information.
Techniques and types of needles used for renal biopsies
Several techniques are fully described in the literature, including surgical biopsies via laparotomy; via laparoscopy; key hole technique; percutaneously, with blind or ultrasound guided techniques. The used tools are also numerous. Renal biopsies may be taken using the Franklin modified Vim-Silverman biopsy needle, Modified Menghini needle; Tru-cut biopsy needle; Actually several devices (guns) can utilize specifically adapted tru-cut needle that may be used several times, allowing a fast and precise execution particularly if it is ultrasound guided. The author is using a Bard® MagnumTM biopsy instrument with a core tissue biopsy needle (16-18G X 20cm length). In case of renal masses, when the collection of cells may be helpful for the diagnosis (e.g., in case of renal neoplasia, renal lymphoma), also the percutaneous fine needle technique may be useful. The kidney chosen to perform the biopsy may be one of each sides. The right one is more fixed, placed at the level of the twelfth intercostals space and it may be more useful for performing the fine needle aspirate; In case of percutaneous ultrasound guided biopsy, the left kidney, being more mobile, offers better exposition (with the patients on the right side recumbency) and evaluation of the part to be biopsied; usually the caudal pole is the place more utilized for such sampling. The specimen is then fixed in 10% buffered formalin, and wax embedded for light microscope evaluation, or in 3% phosphate buffered glutaraldeide for electron microscopy. Several kind of staining may be used for the specimen: hematossilin and eosin is the most commonly used for general assessment of all components of renal parenchyma; Carbohydrates and carbohydrate-protein complexes may be stained with periodic acid-Shiff (PAS); Red congo is useful to detect amyloid presence; Masson's trichrome stain is useful to visualize connective tissue. Usually, to avoid damage to the patient during the biopsy performance it may be necessary to restrain the dog or cat with very light sedation/anesthesia: very low dosage of propofol, injected intravenously to control the patient for few minutes is very efficient and safe. In case of longer work, like during the preparation of dogs for hemodialysis, when kidney biopsy is associated to a dual lumen catheter insertion in the external jugular vein, using venotomy technique or not, depending from the type of catheter is used, a longer anaesthesia is required; induction by mask and maintenance with isofluorane allows also a safe management of the patients; in this case we usually ventilate mechanically, with positive pressure, the patient whilst a careful monitoring of the blood pressure is performed and proper dosage of dopamine in CRI is given to support diuresis, by vasodilation, and to control the arterial blood pressure.
When kidney biopsy is useful?
Basically we propose the kidney biopsy in three major cases:
1. when we have to decide for a patient with chronic development of renal failure that is under treatment with traditional fluid and pharmacology therapy and we are asked by the owner for a definitive prognosis;
2. when we have to decide if to put a patient in hemodialysis and we need to differentiate between a potential reversible acute renal lesion (e.g., tubular lesions) and chronic lesions with less possibility of recovery (e.g., immunomediated diseases with serious involvement of the glomeruli structures;
3. in case of serious proteinuria associated or not to hypertension.