1. Kidneys and adrenals
The kidneys must be viewed in both sagittal and transverse planes and a systematic approach is essential.
• Difference of >1.5 cm between the two kidneys is suggestive of a unilateral pathological process
• Cortex is homogenous (generally equal or less echoic compared to liver or spleen)
• Thickness of preserved renal cortex usually correlates with renal function
• Central echogenic complex contains the hilar vessels and intra-renal collecting system
• Splaying of the central echogenic complex is seen in hydronephrosis
• US is excellent at distinguishing between solid and cystic masses over 2 cm
• Cystic masses are typically spherical with a clearly defined thin wall and demonstrate no internal echoes allowing enhancement of ultrasound transmission. These are generally benign and therefore require no further scrutiny (US diagnostic accuracy virtually 100%)
• Presence of internal echoes, poorly defined walls, and lack of ultrasound transmission is characteristic of a solid mass (USS diagnostic accuracy >84%) and CT evaluation is mandatory
• Diagnostic accuracy of USS for hydronephrosis is 90-100%
• USS cannot distinguish between obstructive and non-obstructive hydronephrosis
• Other conditions mimicking hydronephrosis include congenital megacalycosis, calyceal diverticulum, parapelvic cysts and prominent extrarenal pelvis
• Conversely, early obstruction, dehydration, and urine extravasation can result in false negatives
• A resistive index (RI) of >0.7 can help distinguish between obstructive and non-obstructive hydronephrosis
RI = max renal artery blood flow (RBF) - min RBF / max RBF
• The extent of dilatation may also be evident (e.g., renal pelvis, ureteric, or bladder)
• Renal artery stenosis, renal vein thrombosis, and aretriovenous fistulae can easily be demonstrated using color Doppler
• Urinoma, hematoma, and perinephric abscess can be diagnosed and, in many instances, treated using ultrasound-guided drainage techniques
• Lymph node enlargement, retroperitoneal tumors, and the aorta can be seen using USS
• USS visualization is very useful, especially in children
• Small lesions may be missed and a CT scan is advisable in case of persisting doubt
The bladder can be scanned using the following approaches—
The transurethral approach provides excellent definition and can be useful in the evaluation of muscle invasion by tumors. The 5.5 MHz transducer (either 900 or 1350) fits within a standard resectoscope. The full bladder should be anechoic and therefore stones, tumors, debris, clots, and infection may cause abnormal echoes.
Bladder urine volume can be measured although inaccurately (volume = height x width x depth/2). Absence of ureteric jets (seen using color Doppler) for >15 min is suggestive of ureteric obstruction. Lower ureteric and vesicoureteric stones can be demonstrated using the transabdominal USS technique.
High-frequency, small-parts transducers permit high-quality sonographic evaluation of scrotal contents for abnormal masses (solid and cystic), inflammatory conditions, and blood flow. Doppler flow measurements have a 98% accuracy rate in the diagnosis of acute testicular torsion, but in most cases immediate surgical exploration (rather than USS) is recommended. Doppler studies may also demonstrate high blood flow in the presence of varicoceles and inflammation.
USS of the penis has been used for the following conditions:
1. Impotence: doppler studies can demonstrate cavernosal and internal pudendal blood flow
2. Peyronie's disease: the area of fibrosis or plaque formation is often seen easily using USS
3. Priapism: USS can help differentiate between high-flow (due to arteriovenous fistula) and low-flow priapism
4. Urethral strictures: strictures of the distal urethra and peri-urethral structures can be seen clearly using USS, avoiding the need for unnecessary radiation
Intra-operative ultrasound (IUSS) allows visualization of tissues without distortion by abdominal organs, bowel gas, and bony structures and will be used increasingly in the future. Applications for renal surgery include assessment of—
• Whether a tumor is amenable for partial nephrectomy by delineating tumor anatomy
• Local vasculature using color Doppler
• Renal vein involvement by tumor
• Use of real-time laparoscopic IUSS for laparoscopic renal cryo-surgery and high-intensity focused ultrasound (HIFU)
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