Indications Cystography is used to demonstrate: \200 bladder anatomy; \200 urinary leak s (which are usually iatrogenic); \200 vesico-enteric \201 stulae; \200 ureteric re \202 ux; \200 urethral anatomy. Primary signs of stone disease \200 Calculus within the ureteric lumen. Secondary signs o f stone disease \200 Hydronephrosis. \200 Perinephric or periureteric stranding. \200 Ureteric dilatation. \200 Blurring of the sinus fat. \200 Enlarged kidney. CT with int ravenous contrast enhancement Scanning is performed after the intravenous injection of cont rast media (Fig. 1.6.6). The acquisition of images at dif- ferent times after injection pro vides additional information: Arterial: This is used to image renal arteries primarily for evidence of renal artery stenosis. To optimize the visualiza- tion of the arteries, bolus t racking is done \201 rst so that the scan can be performed at the time of peak enhancemen t of the aorta. Corticomedullary phase: 25 \200\22380 s post injection. During this phase t he cortex is enhanced while the (hypovascular) medulla remains relatively unenhanced. It is useful for evaluating the vascularity of tumors and in \202 ammatory lesions. Hypovascula r medullary tumors or hypervascular cortical tumors may, however, be missed during this pha se. Nephrographic phase: 85 \200\223100 s post injection. The renal parenchyma should appea r homogeneous during this phase. This is the best phase for detecting and evaluating renal lesions. Fig. 1.6.4 Cystogram. (a) Bladder, and (b) urinary re \202 ux into the collecting system o f a transplant kidney. Ascending urethrography Contrast is introduced into the urethra through a narrow- bore cath eter and X-ray images are obtained (Fig. 1.6.5). It provides good anatomical detail of the urethra and can be performed by ultrasound or \202 uoroscopy. Indications \200 Following trauma it is used to demonstrate continuity of the urethra and urethral leaks. To evaluate penile strictures prior to intervention. Y. REES 24 Fig. 1.6.6 CT scanning in renal disease. 1. Abdominal CT scan without contrast showing a ca lculus in the mid-ureter with stranding around it (arrow). 2. CT scan without contrast show ing (a) a dilated pelvis and (b) peri-renal stranding. 3. CT scan without contrast demonstr ating a small solid lesion (arrow) containing fat (low attenuation), therefore most likely to be an angiomyolipoma. 4. CT scan with contrast demonstrating (a) a normal right kidney, (b) a left renal tumor, and (c) remaining normal renal parenchyma on the left. 5. Reconstru cted CT scan with contrast demonstrating (a) a normal right kidney, (b) a renal tumor in th e left upper pole, (c) normal lower pole of the left kidney, (d) normal liver, and (e) sple en. 6. CT scan demonstrating multiple bladder tumors (arrowheads). 7. CT urogram demonstrat ing (a) contrast in the right collecting system, and (b) a \201 lling defect in the colle cting system consistent with a transitional cell carcinoma. CHAPTER 1.6 Imaging in renal disease 25 Excretory phase: 3 \200\2235 min post injection. The collecting sys- tem is enhanced and th is is primarily useful in detecting urothelial lesions (see \200\230CT urography \200\231 below). Nephrotoxic contrast agents are avoided. The risk of neph- rogenic systemic \201 brosis n eeds to be considered in those with impaired renal function. Indications \200 To stage urogenital cancers: may be used in conjunction with MRI. To demonstrate obstruction, the level of obstruction, and its cause. If contrast is given, calculi may be more dif \201 cult to identify. To demonstrate collections associated with the renal tract, e.g. perinephric collections. To demonstrate soft tissue abnormalities related to the renal tract, e.g. retroperitoneal \201 brosis. To demonstrate mass lesions in the renal tract. \200 To differentiate cystic from solid t umors. \200 To characterize the vast majority of angiomyolipomas so that they do not require tissue con \201 rmation. To aid in the diagnosis of infection, including tuberculosis. \200 To evaluate the renal tract after trauma to demonstrate: the anatomy of the renal tract and any pre-existing anom alies; the type and severity of parenchymal injury; the extent of perinephric hemorrhage; u rinary extravasation/leaks; injuries to the vascular pedicle. \200 \200 \200 CT urography The patient \201 rst undergoes a noncontrast enhanced scan to exclude calci \201 cation. This is followed by an arterial phase scan to demonstrate enhancing tumors in cluding transitional cell carcinomas. A \201 nal scan is undertaken 5 \200\2237 min after the IV injection of contrast media, by which time contrast has accumulated in the collecti ng system (Fig. 1.6.6). It is undertaken mainly to diagnose congenital abnormali- ties of t he urinary tract, and to detect and evaluate urothe- lial lesions (e.g. transitional cell c arcinomas). Magnetic resonance imaging Indications \200 To characterize renal mass lesions (Fig. 1.6. 7). Noncontrasted and gadolinium-enhanced T1-weighted scans are undertaken during the phase s described under contrasted CT. To stage bladder and prostate carcinomas. \200 To assess tumor thrombus in renal tumors. MRI does not require iodinated contrast media but the risk of nephrogenic systemic \201 b rosis if gadolinium-based MR contrast agents are used in patients with reduced GFR must be considered. There is no cross-sensitivity between iodinated contrast agents and MR contrast agents. The risk of anaphylaxis with MR contrast agents is 0.04%. MRI may be used in earl y pregnancy. Fig. 1.6.7 MRI of the renal tract. 1. MRI demonstrating multiple bladder tumors (arrowheads ). 2. MR angiography demonstrating (a) left ostial renal artery stenosis, (b) normal right renal artery, (c) aorta, and (d) iliac artery. 3. MR urogram demonstrating (a) left hydrone phrosis, (b) dilated left ureter, (c) a ureteric \201 lling defect, and (d) the bladder. MR angiography This is an effective and noninvasive method to evaluate renovascular disease in native kidneys (Fig. 1.6.7). For the diagnosis of renal artery stenosis the sensitivity is >93% and the speci \201 city >83%. No radiation is required. MR urography This can be an effective method for imaging the urinary tract (Fig. 1.6.7). It provides good anatomical detail but the resolution is not as good as CT. It can be underta ken in two ways: \200 Heavily T2-weighted image acquisition provides good detail of stati c \202 uid in the collecting system, particularly Y. REES 26 when it is obstructed and dilated. IV contrast is not required, therefore this method is us eful even in the absence of urine production. T1-weighted images can be obtained during the excre- tory phase following IV gadolinium inj ection. This is analogous to CT urography. Nuclear medicine Nuclear medicine techniques can provide both functional and structural inf ormation in the investigation of renal disease. There are broadly three types of nuclear me dicine study: \200 GFR estimation (this is discussed in Chapter 1.3). \200 Dynamic: ser ial scans are obtained to determine uptake, transit and excretion of the tracer. Static: tracer is taken up and retained in the kidney. Scanning is performed in multiple pr ojections to identify structural abnormalities. The four most widely used radiopharmaceuticals are: \200 [51Cr]Ethylenediamine tetra-acet ic acid ([51Cr]EDTA). It is excreted exclusively by glomerular \201 ltration and is used for the accurate estimation of GFR. It is not used for imaging. [ 99mTc]Diethylenetriamine penta-acetic acid ([99mTc]DTPA). Again this is excreted by glome rular \201 ltration. It is used in dynamic imaging studies. This has fallen out of favor and is being replaced by [99mTc]MAG3. [99mTc]Mercaptoacetyltriglycine ([99mTc]MAG3). This is excreted by tubular secretion. It is used in dynamic stud- ies and produces better scintigraphic images than [99mTc]DTPA, parti cularly when the GFR is reduced. \200 [99mTc]Dimercaptosuccinic acid ([99mTc]DMSA). This compound becomes retained and concentrated in the renal cortex and is therefore used in sta tic studies to provide high resolution anatomic images. Dynamic renography [99mTc]MAG3 (or [99mTc]DTPA) is usually used in these studies. Indicatio ns \200 To determine the percentage of renal function contrib- uted by each kidney. To diagnose obstruction. IV furosemide is often given as part of this study (diuresis renography) (Fig. 1.6.8). To differentiate obstruction from a dilated, but nonob- structed, collecting system. To assess renal perfusion. \200 To assess perfusion and urine drainage in a renal transplant. Fig. 1.6.8 Radioisotope studies. 1. Renogram showing left-sided obstruction. (a) Normal rig ht kidney trace. (b) Accumulation of tracer isotopes after furosemide. (c) Persistence of t racer in the left kidney on delayed imaging. 2. DMSA renogram: (a) a normal right kidney an d (b) a scarred left kidney. 3. DMSA renogram demonstrating multiple photopenic areas due t o cysts in polycystic kidney disease. To evaluate potential renal artery stenosis (RAS). Captopril is often used as part of this study since in the presence of signi \201 cant renal artery stenosis, renal per- fusion is dependent on angiotensin II. A captopril-induced fall in GFR (determined by reduced and de layed uptake of tracer) is suggestive of RAS. Static renography [99mTc]DMSA is used in these studies (Fig. 1.6.8). Indications \200 To accurately assess the percentage of function contrib- Other nuclear medicine studies used in renal medicine Isotope bone scintigraphy [99mTc]Diph osphonate or polyphosphonate becomes \201 xed to hydroxyapatite in bone. Therefore uptake of tracer is increased in areas of high bone turnover. uted by each kidney. To demonstrate renal scarring or other anatomical abnormalities of the parenchyma. To localize ectopic renal tissue. CHAPTER 1.6 Imaging in renal disease 27 It is useful in identifying metastatic lesions in bone, particu- larly from prostate carcin oma. However, it is unhelpful in myeloma since bone deposits to not incorporate the tracer. Cystic brown tumors (of hyperparathyroidism) may also not take up the tracer. Complications Immediate Pain. This is common and should be anticipated. Bleeding: \200 Mi nor bleeding is common, and requires no treatment. \200 In <4% of cases bleeding is heavy and may require trans- fusion. Less commonly bleeding continues, and emboli- sation of the bleeding point, or (even more rarely) nephrectomy may be needed. Percutaneous nephrostomy This involves the percutaneous insertion of a catheter into the re nal pelvis (Figures 1.6.9 and 1.6.10). Catheter blockage as a result of clots. Infection: <4% risk of bacteremia. Pneumothorax. Pe rforation of other abdominal organs. Failed access <5%. Death. This is rare. Indications Emergency indications: \200 Drainage of a pyonephrosis. \200 Drainage of a kidney in a patient with acute kidney injury caused by obstruction. Other indications: \200 Drainage of an obstructed kidney. \200 Diversion of urine from the collecting system to allow Long-term Infection. Catheter blockage. Therefore long-term nephrostomies require regular c hanging. Catheter displacement. leaks or \201 stulae (iatrogenic or otherwise) to heal. To provide access for other endourological procedures, e.g. antegrade stenting, percutaneou s nephrolithotomy, pyeloplasty. To provide access for the administration of drugs/ treatments, e.g. chemotherapy, solutions for stone dissolution. Nephrostogram: after the procedure, contrast can be injected via the nephrostomy catheter a nd the site of obstruction can be determined. Preassessment Full blood count and coagulation studies. Although abnor- mal coagulation is not an absolute contraindication, all efforts should be made to reverse the abnormalities b efore the procedure is undertaken. If coagulation abnormalities are severe and/or not corre ct- able, alternative approaches should be considered, e.g. retrograde ureteric stenting. O btain informed consent. Administer prophylactic antibiotics (even if the patient is not ove rtly septic prior to the procedure). Fig. 1.6.9 Nephrostogram showing urinary leak. (a) Nephrostomy catheter, (b) pelvicalyceal system, (c) ureter, and (d) contrast extravasation. Procedure It is usually performed under ultrasound guidance but fluoroscopic or CT guidance may also be used (Fig. 1.6.10). The patient is placed in the prone oblique position. If po ssible, the skin puncture is made under the 12th rib to prevent pneumothorax, and lateral t o the paraspinous muscles. Local anesthetic is applied. The kidney puncture is made at the tip of a calyx, usually in the lower pole, to avoid the arcuate arteries. The track through the kidney should be posterolateral through the renal parenchyma. This ensures that the re latively avascular zone (Broedel \200\231s line) is traversed and avoids direct entry to th e pelvis which is associated with more complications (laceration of renal pelvis, bleeding from large hilar vessels). A wire is placed through the puncture needle and is manip- ulate d into renal pelvis. The tract is dilated over the wire. The nephrostomy catheter is insert ed and secured. Arteriography Inspite of the advent of newer imaging techniques, arteri- ography remains th e \200\230gold standard \200\231 investigation for reno- vascular disease. It is an invasi ve investigation, therefore renal arteriography should only be performed as a prelude to a therapeutic procedure. It should not be used as a screening test. Indications \200 Renovascular disease. It may con \201 rm the presence of RAS. Renal art ery angioplasty and/or stenting can be undertaken at the same time. Acute renal ischemia. Renal artery thrombosis or embolization may be diagnosed which may be amenable to thrombolysis. Unexplained macroscopic hematuria (after full urological evaluation). It may identify arter iovenous mal formations or angiomata that may be amenable to embolization. \200 Polyarter itis nodosa. Arteriography may identify intrare- nal microaneurysms. Y. REES 28 Bleeding post renal biopsy. To identify site of bleeding Diabetes mellitus: particularly when associated with and possibly allow embolization. impaired renal function. Renal trauma. Embolization to control bleeding may be Volume depletion. \200 Concurrent use of nephrotoxic drugs, e.g. NSAIDs. \200 Heart fai lure. \200 Gout. \200 Age >70 years. Preventative measures \200 If possible, use alte rnative imaging tests which do not possible (Fig. 1.6.11). Venography/ \201 stulography These investigations are used in the preparation for, and the management after, arteriovenous \201 stula (AVF) formation. Indications \200 To assess the vessels for anatomical mapping prior to require iodinated contrast agents. AVF formation. Stop nephrotoxic drugs before the study. \200 Ensure patients are volume replete. Start I V volume expansion to induce a diuresis before the study (unless this is contraindicated by heart failure or advanced CKD with volume overload). To assess vascular problems in a \201 stula, e.g. poor \202 ow, recirculation, high ven ous pressure. Ultrasound with or without Doppler ultrasound may be used in conjunction with \201 stulography. In some cases \201 stuloplasty can be undertaken to treat Use nonionic contrast agents. \200 Use the smallest dose of contrast required to obtain t he \201 stula strictures (Fig. 1.6.12). Contrast-induced nephrotoxicity Risk factors \200 Pre-existing renal disease: the risk of nephrotoxity is proportional to the severity of the underlying renal disease. diagnostic result. Currently there is insufficient evidence that other strategies (e.g. N-acetylcysteine or so dium bicarbo- nate infusion) can protect against contrast-induced nephrotoxicity. Fig. 1.6.10 Nephrostomy procedure. 1. Hydronephrotic kidney punctured with needle. 2. Guide wire placed through needle. 3. Tract dilated. 4. Pigtail catheter inserted. CHAPTER 1.6 Imaging in renal disease 29 It is a progressive, sometimes fatal disease affecting the skin, muscle and internal organs , including striated muscle, myocardium and lungs. It manifests with erythema, plaques, a p eu d \200\231orange appear- ance, and induration initially on the legs. A typical distribut ion of lesions is from the ankles to below the knees, the mid-thighs, and between the wrist s and upper arms. It progresses to involve other parts of the body and ulti- mately involve s tendons and peri-articular tissues causing contractures and immobility. The trunk is less commonly affected and the head is spared. Fig. 1.6.11 Renal arteriography for renal bleeding. 1. Arteriogram. (a) Catheter, (b) upper pole arteries, (c) lower pole arteries, (d) extravasation of contrast. 2. Arteriogram post -coil embolization. (a) Catheter, (b) lower pole renal artery, (c) coils with no further co ntrast extravasation. Nephrogenic systemic \201 brosis (NSF) This is a rare scleroderma-like skin condition tha t affects patients with renal insuf \201 ciency. It was \201 rst described in 1997. It w as previously called nephrogenic \201 brosing dermopathy, although with the realization t hat the sclerosis was not skin-limited, the term NSF has been adopted. Recent evidence has suggested that gadolinium-containing contrast agents (particularly gadodiamide (Omniscan), and gadopentetic acid (Magnevist)) may play a role in causing this disorder (>95% of patien ts with NSF have been exposed to gadolinium). It occurs exclusively in patients with modera te-to-severe renal failure (there are no reports in patients with GFR >60 mL/min). It has b een seen mainly in hemodialysis patients, but can also occur in patients: on peritoneal dia lysis; with failing renal transplants; and with severe renal impairment not requiring dialy sis (GFR <30 mL/min/1.73 m2). It has been associated with liver failure and liver transplan - tation, although always in association with renal failure. An association with the use of erythropoietin-simulating agents has been suggested but not established. Male:female invol vement is equal. The majority of cases are in patients aged 45 \200\22350 years, although c hildren can also be affected. Cases have been reported in Europe, USA and Asia. Fig. 1.6.12 Fistulogram and \201 stuloplasty. 1. Fistulogram of a brachio-cephalic AVF de monstrating (a) the cephalic vein, (b) the \201 stula, and (c) a tight stenosis in the ve in. 2. Post- \201 stuloplasty the cephalic vein is widely patent (arrow). Histologically the appearances are different from systemic sclerosis. Early changes include dermal \201 brocyte prolifera- tion, with progression to extensive dermal thickening and \201 brocyte proliferation in advanced disease. Gadolinium can usually be identi \201 e d in the skin if appropriate investiga- tions are undertaken. There is currently no effecti ve treatment. Restoration of renal function with renal transplantation offers the best hope for improvement in symptoms. Prevention If possible, avoid gadolinium in high risk patients (i.e. those with GFR <30 mL/ min, and those with concurrent liver disease) through the use of alternative imaging modali ties. Y. REES 30 Gadodiamide (Omniscan) is contraindicated in patients with impaired renal function (GFR <30 mL/min). Other gadolinium-based contrast agents should be used with caution in patients wi th severe renal impairment (GFR <30 mL/min/1.7 m2). The minimum dose of contrast agent that gives the desired diagnostic information should be used. It is suggested that the dose of any gadolinium-based contrast agent should not exceed 0.3 mmol/kg. In patients on hemodialy sis it is sensible to dialyse the patient as soon as possible after the procedure, and then again 24 h later. There is no evidence, however, that this will prevent the development of NSF. Patients with CKD 5 who are not currently on dialysis should not be commenced on hemo dialysis purely to enhance gadolinium removal. The risks of establishing access for hemodia lysis and the procedure itself outweigh the risks of developing NSF. Sutton D, Reznek R, Mur \201 tt J. Textbook of radiology and imaging, 5th edn. Edinburgh: Churchill Livingstone; 2002. Internet resources Guidelines on the use of gadolinium-based contrast agents: http://www.esur.org/Nephrogenic_Fibrosis.30.0. html Information about gadolinium-based cont rast agents and risk of NSF: http://www.mhra.gov.uk Information about gadolinium-based contrast agents and risk of NSF: http://www.fda.gov Gadolinium-bases Contrast Media and Nephrogenic Systemic Fibrosis: http://www.rcr.ac.uk/docs/radiology/pdf/ BFCR0714_Gadolinium_NSF_guidanceNov07.pdf ESUR Gui delines on contrast media version 6.0: Further reading Federle M, Brooke JR, Venkat Sridhar A. Diagnostic Imaging: Abdomen http://www.esur.org/fileadmin/Guidelines/ESUR_ 2007_Guideline_6_Kern_Ubersicht.pdf (Diagnostic Imaging). AMIRSYS; 2004. Grainger & Allison \200\231s Diagnostic Radiology: A Textbook of Medical See also Drug-induced nephropathies, p. 698 Dermatologic disorders in CKD, p. 450 Imaging, 5th edn. Edinburgh: Churchill Livingstone; 2007. Royal College of Radiologists. Making the best use of clinical radiology services, 6th edn. London: RCR; 2007. This page intentionally left blank P. TOPHAM 32 Renal biopsy Lupus nephritis This can usually be diagnosed using noninvasive criteria. However a renal b iopsy will clarify the type of pathological lesion, and will indicate the level of acute ac tivity and the degree of chronic damage. This provides a robust basis for evidence-based tr eatment. Percutaneous renal biopsy was \201 rst described in the early 1950s. Since then the proce dure has been re \201 ned and now provides a tissue diagnosis in >95% of cases with a life - threatening complication rate of <0.1%. Indications The biopsy should be able to provide a speci \201 c diagnosis, re \202 ect th e level of disease activity, and guide the use of appropriate treatment. Common indications for renal biopsy are listed in Table 1.7.1. Other diseases Amyloidosis, sarcoidosis, allergic drug reactions, and mye- loma can all be diagnosed on renal biopsy. Renal biopsy is reserved for those cases where the diagnosis can not be made by noninvasive means. Table 1.7.1 Indications for renal biopsy Renal transplant dysfunction In the absence of ureteric obstruction, urinary sepsis, renal artery stenosis, or toxic levels of calcineurin inhibitors, a renal biopsy is required to d etermine the cause of renal allograft dysfunction. Nephrotic syndrome Acute renal failure Systemic disease with renal dysfunction Renal transp lant dysfunction Nonnephrotic proteinuria Isolated microscopic hematuria Unexplained chroni c renal failure Familial renal disease Non-nephrotic proteinuria The value of renal biopsy in this situation is unclear. If pro- t einuria is >1 g per day a renal biopsy can be justi \201 ed since it will provide prognost ic information, may identify a disease for which a different therapeutic approach is needed , and may provide clinically important information about the future risk of disease recurre nce following renal transplantation. Nephrotic syndrome The cause of nephrotic syndrome cannot be reliably pre- dicted noninvasi vely in adults and older children after puberty; a renal biopsy is therefore indicated. In children between 1 year and puberty, a presumptive diagnosis of minimal change disease can be made. Renal biopsy is reserved for those with atypical features (micro- scopic hematuria , reduced complement levels, persistent renal impairment, nonresponse to steroids). Isolated microscopic hematuria If a structural cause for microscopic hematuria has been rul ed out, a glomerular source for the hematuria needs to be considered. 50 \200\22375% of suc h patients will have a glomerular lesion with IgA nephropathy being the commonest abnormali ty. However, in the absence of hypertension or proteinuria the renal prognosis is excellent . In such cases a renal biopsy will only provide diagnostic information and is unlikely to alter therapy and therefore is often not considered necessary. Renal biopsy should be perfo rmed only if the result would provide reassurance to the patient, avoid repeated urologi- c al investigations, provide speci \201 c information (e.g. in the evaluation of potential l iving kidney donors), or for life insurance and employment purposes. Acute kidney injury In most cases of acute kidney injury the cause (pre-renal, obstruction, acute tubular necrosis) can be con \201 dently diagnosed without a renal biopsy. However, if a con \201 dent diagnosis cannot be made a renal biopsy should be under- taken urgentl y, particularly if there is an active urine sediment (microscopic hematuria, proteinuria, a nd cellular casts). Renal dysfunction with systemic disease Diabetes mellitus If the clinical setting is compat ible with diabetic nephropa- thy (isolated proteinuria, diabetes of long duration, evi- den ce of other microvascular complications) a biopsy is not necessary. However, the presence o f atypical features (microscopic hematuria with or without proteinuria, absence of retin- o pathy or neuropathy (type 1 diabetes only), proteinuria within 5 years of onset of diabetes , atypical changes in renal function or the presence of immunologic abnormalities) should p rompt consideration of a renal biopsy. Unexplained chronic renal failure A renal biopsy in patients with chronic renal failure and normal-sized kidneys can be informative. It may identify unexpected pathology in almost 50 % of cases. If the kid- neys are small (<9 cm) the risks of the biopsy are increased and th e utility may be compromised by extensive glomeru- lar and tubulo-interstitial \201 brosi s which is not amenable to any speci \201 c therapy. Familial renal disease A biopsy performed on one family member may secure the diagnosis for the whole family and avoid the need for repeated investigation. Conversely a renal biopsy may unexpectedly identify a lesion that has a hereditary basis and prompt investigation of other family members. Systemic vasculitis and Goodpasture \200\231s disease Even though the availability of serol ogic testing for MPO- and PR3-specific ANCA and antiglomerular basement membrane antibodies allows a con \201 dent diagnosis of renal vasculitis or Goodpasture \200\231s disease to be made in many cases, a renal biopsy should still be performed in order to con \201 rm th e diagnosis and to clarify the degree of active in \202 ammation and chronic scarring. Thi s will help guide the type and intensity of immunosuppressive treatment. Pre-biopsy evaluation Before undertaking a renal biopsy it is important to identify issues that may compromise the safety of the procedure. The pre-biopsy evaluation is shown in Tabl e 1.7.2. Evaluation should determine whether the patient has: two normal-sized unobstructed kidneys; sterile urine; CHAPTER 1.7 Renal biopsy 33 controlled blood pressure; and no abnormality of coagulation. The value of the bleeding tim e in this setting has never been prospectively tested. Retrospective studies have shown a t hree- to \201 ve-fold increase in bleeding complications after renal biopsy in patients w ith prolonged bleeding times. Prospective studies in liver biopsy patients have shown a \201 ve-fold increase in bleeding complications in those with uncorrected bleeding times. T here is a consensus view that the bleeding time is a poor predictor of post-surgical bleedi ng, but that it does corre- late with bleeding episodes in uremic patients. For this reason many centers include the bleeding time in their pre-biopsy evaluation and if prolonged bey ond 10 min administer 1-desamino-8-D-arginine (DDAVP). An alternative but equally acceptabl e approach is to administer DDAVP to all patients with signi \201 cant uremia (urea >20 mm ol/L or serum creatinine >250 mol/L) without performing a bleeding time. to the mortality associated with a general anesthetic. Therefore percutaneous biopsy of a s olitary kidney can be justi \201 ed in the absence of risk factors for bleeding. Table 1.7.3 Contraindications to renal biopsy Kidney status Multiple cysts (R) Solitary kidney (R) Acute pyelonephritis/perinephric abces s (R) Renal neoplasm (R) Patient status Uncontrolled bleeding diathesis (A) Uncontrolled blood pressure (R) Uremia ( R) Obesity (R) Uncooperative patient (R) A, absolute contraindication; R, relative contraindication. Renal biopsy technique Percutaneous renal biopsy Native renal biopsy Typically a renal biop sy is performed by nephrologists using continuous (real-time) ultrasound guidance and dispo sable automated biopsy needles. 16 gauge needles may be used as a compromise between the gr eater tissue yield of larger needles and the trend to fewer bleeding complications of small er needles. \200 Sedation is only rarely required. \200 The patient lies prone with a p illow under the abdomen Table 1.7.2 Renal biopsy work-up Pre-biopsy requirement 2 normal-sized, unscarred, unobstructed kidneys Renal imaging Systolic BP <160 mmHg, diastolic <95 mmHg Blood pressure Sterile \200 No aspirin, clopidogrel, NSAID, Urine culture Coagulation status to straighten the spine and splint the kidneys. warfarin for 1 \200\2232 weeks pre-biopsy Ultrasonography is used to localize the lower pole of the kidney to be biopsied and the ski n is marked with an indelible pen at the point of entry of the biopsy needle. \200 The sk in is then prepped and anesthetized with 1 \200\2232% Platelet count >100 \227 109/L \200 Prothrombin time <1.2 times control \200 Activated partial thromboplastin time <1.2 \227 control (if prolonged consider presence of lupus ant icoagulant) \200 Bleeding time <10 min (measure if urea >20 mmol/L) (see text). If prolon ged (or if urea >20 mmol/L, high risk biopsy, and bleeding time unavailable (see text)) giv e DDAVP 0.4 g/kg 3 \200\2234 h before the biopsy. lidocaine. Under ultrasound guidance a narrow gauge spinal nee- dle is advanced to the renal capsule a nd further local anesthetic is in \201 ltrated along the needle track. A stab incision is made through the dermis to ease pas- sage of the biopsy needle. The biopsy needle is directed under ultrasound guidance towards the kidney capsule. The biopsy is taken after patients are instructed to hold their breath. The biopsy needle i s withdrawn immedi- ately and the patient resumes breathing. Contraindications to renal biopsy These are listed in Table 1.7.3. Absolute An uncorrectable bleeding diathesis is the only absolute contraindication to percu taneous biopsy. If the biopsy is indispensable alternative approaches can be used (open bio psy, laparoscopic biopsy, or transvenous (usually transjugular) biopsy). Usually a second core of tissue is required for immun- o \202 uorescence and electron microscopy. If insuf \201 cient material is obtained, further passes of the needle can be made. There is a modest increase in the postbiopsy complication rate if the needle is passed more than four times. Once suf \201 cient renal tissue has been obtained the skin incision is dressed and the pa tient is rolled directly into bed for observation. Relative Hypertension (>160/95), hypotension, perinephric abscess, pyelonephritis, hydronep hrosis, severe anemia, large renal tumors, and renal cysts are all relative contraindicatio ns to renal biopsy. Where possible they should be corrected before undertaking the biopsy. The presence of a solitary functioning kidney is considered to be a relative contraindicati on to percutaneous biopsy. It has been argued that performing the biopsy with direct visual ization is required in this circumstance. However, the postbiopsy nephrectomy rate of 1:200 0 to 1:5000 is similar Since no single \201 xative allows good quality immuno \202 uores- cence, light or elect ron microscopy to be performed on the same sample, the biopsy cores are divided into three and placed in: \200 Formalin for conventional light microscopy. \200 Normal saline for subsequent snap-freezing in liquid nitrogen for immuno \202 uorescence microscopy. Glutaraldehyde for electron microscopy. P. TOPHAM 34 There are a number of variations of the percutaneous renal biopsy technique. For example, s ome operators use ultrasound to localize the kidney and to determine its depth and the angl e of approach of the needle. The biopsy is then performed without further ultrasound guidan ce. The success and complication rates of this technique appear to be no different from tha t seen with continuous ultrasound guidance. Computed tomography guidance has been advocated for patients in whom the biopsy can be technically challenging. Alternatives to the percutaneous approach When a percutaneous approach is contraindicated, alter- native approaches to renal biopsy have been described. The choice of technique in an y situation depends on the safety, morbidity, recovery period, and adequacy of the techniqu e, but above all on the local expertise that is available. Transvenous (transjugular or transfemoral) renal biopsy Transvenous sampling of the kidney is theoretically safer than the percutaneous approach because: \200 the needle passes fro m the venous system into the renal parenchyma and is directed away from large blood vessels ; Renal transplant biopsy The general technique for renal transplant biopsy is similar to tha t of the native kidney. The proximity of the allograft to the anterior abdominal wall and t he lack of movement on respiration facilitate its biopsy. If the biopsy is being performed to identify the cause of acute allograft dysfunction a formalin- \201 xed sample for con- ventional light microscopy is usually suf \201 cient. A snap-fro- zen sample for C4d immun ostaining should be obtained if antibody-mediated rejection is suspected. If recurrent or d e-novo glomerulonephritis is suspected, additional sam- ples for electron microscopy and im muno \202 uorescence microscopy should be collected. it is suggested that any bleeding that occurs should be directed back into the venous system; if capsular perforation occurs, signi \201 cant bleeding points can be immediately identi \201 ed and controlled by coil embolization. The transjugular renal biopsy cannot be regarded as rou- tine because it requires specialis t skill, and involves addi- tional time and expense. Indications for this approach are: \200 an uncontrollable bleeding diathesis; \200 the need to obtain tissue from more than one organ Post-biopsy monitoring Following the biopsy the patient is placed supine and is put on stri ct bed rest for 6 \200\2238 h. The blood pressure is monitored frequently, the urine is exa mined for macroscopic hematuria, and the skin punc- ture site is examined for excessive ble eding. If after 6 \200\2238 h there is no evidence of bleeding the patient is sat up in bed and subsequently allowed to mobilize. If macroscopic hematuria develops, bed rest is conti nued until the bleeding settles. Historically patients were observed in hospital overnight following the renal biopsy. including the kidney, liver, or heart; large volume ascites (precludes the prone position); \200 uncontrolled hypertension; \200 morbid obesity; \200 severe respiratory insuf \201 ciency; \200 solitary right k idney; \200 failed percutaneous approach; \200 coma. Studies report diagnostic yields f or transjugular biopsy of between 73 and 98%. Despite these being high risk patients, the c omplication rate appears to be similar to that seen in percutaneous renal biopsy Day case renal biopsy Day case renal biopsy with same-day discharge after 6 \200\2238 h of observation has become increasingly popular. This has been largely driven by the \201 nan cial and resource implications of overnight hospital admission and has been justi \201 ed by the perception that any signi \201 cant complica- tions of renal biopsy will develop wi thin 6 \200\2238 h post-biopsy. However, a recent study has suggested that only 67% of the major complications observed after renal biopsy in 750 patients became apparent within 8 h after biopsy. Up to half of our renal biopsies are performed as day cases. Patients with th e highest risk of complications \200\223 signi \201 - cantly impaired renal function (ser um creatinine >250 mol/L); small kidneys; and uncontrolled hyperten- sion \200\223 shoul d not be considered for a day case renal biopsy. In properly selected cases up to 5% of pat ients can develop a self-limiting postbiopsy complication within 8 h that requires a short hospital admission for observation, and 0.75% of patients return 1 \200\2234 days after sam e-day discharge with either macroscopic hematuria or loin pain due to perirenal hematoma. T ypically such complications settle with conservative management. Therefore, day case biopsy is acceptably safe when a low- risk patient population is selected. Open renal biopsy This is a safe alternative to percutaneous biopsy when uncor- rectable co ntraindications exist. Published studies report tis- sue adequacy of 100% with no major com plications. However, the risk of general anesthesia and the delayed recovery time have prev ented its widespread adoption. It is most useful when a renal biopsy is required in patient s who are undergoing an abdominal procedure for other reasons. Laparoscopic renal biopsy This procedure requires general anesthesia and two lapar- oscopic ports in the posterior and anterior axillary lines to gain access to the retroperitoneal s pace. Laparoscopic biopsy forceps are used to obtain cortical samples, and the biopsy sites are coagulated with laser and packed to pre- vent hemorrhage. The largest published study reported that adequate tissue was obtained in 96% of 74 patients. Signi \201 cant bleeding occurred in three patients, the colon was injured in one, and a biopsy was performed inadv ertently on the spleen and liver in two others. Complications of renal biopsy The complication rates compiled from large series of renal bi opsies are shown in Table 1.7.4. Hemorrhagic CHAPTER 1.7 Renal biopsy 35 complications still occur but other serious complications are now rare. Since most are clinically silent and >95% resolve spontane- ously within two years, routine screening is not recom- mended. Unusually arteriovenous \201 stulae can lead to macrosco pic hematuria, hypertension, and renal impairment, in which case embolization is appropriat e. Table 1.7.4 Complications of renal biopsy (1990 to present) No. of biopsies 3884 Other complications Other rare complications have been reported, including: \200 biopsy o f other organs (liver, spleen, pancreas, bowel, Hematoma 3% Macroscopic hematuria 3% and gallbladder); \200 pneumothorax; \200 hemothorax; \200 calyceal \200\223peritonea l \201 stula; \200 dispersion of carcinoma; \200 Page kidney (compression of the kidn ey by a perirenal hematoma leading to renin-mediated hypertension). Arteriovenous \201 stula formation 0.2% Surgery 1 case Death 1 case