Diagnostic ultrasound ( PDFDrive )

CHAPTER 9 The Kidney and Urinary Tract 341
Imaging and Treatment Approaches
Before the advent of CT, renal tumors less than 3 cm represented
5% of lesions, whereas now these small lesions represent 9% to
38% of all renal tumors. 131 Jamis-Dow et al. 132 found that CT
was more sensitive than ultrasound for the detection of small
renal masses (<1.5 cm) and that both ultrasound and CT could
equally characterize a mass larger than 1 cm. hey also demonstrated
that a combination of ultrasound and CT allowed accurate
characterization of a lesion larger than 1.0 cm in 95% of cases.
With the advent of helical CT, respiratory misregistration and
partial volume averaging are minimal; thus nephrographic-phase
helical CT scans enable better lesion detection and characterization
and typically is suicient for diagnosis. 133-136
A particular role of MRI is in the characterization of highattenuation
renal masses. 137 Most centers, however, still reserve
renal MRI for patients with (1) an allergy to iodinated contrast,
(2) CT-indeterminate renal masses, or (3) extent of vascular
involvement inadequately determined by ultrasound and CT.
Previously, renal MRI was also performed to assess lesional
enhancement in patients with renal insuiciency. However,
recognition of the central role of gadolinium in the development
of nephrogenic systemic ibrosis highlighted the potential risks
in these patients. 138 hus ultrasound has again assumed a preeminent
role for mass characterization in patients with renal
insuiciency at risk for nephropathy ater iodinated contrast
exposure at CT or for nephrogenic systemic ibrosis ater gadolinium
exposure at MRI.
Contrast-enhanced ultrasound (CEUS) also holds promise
for assessment of renal lesions. Quaia et al. compared sonography
without contrast material versus CEUS and CT for the characterization
of 40 complex cystic renal masses and found that the
diagnostic accuracy of CEUS (80%-83%) was better than that
of nonconstrast sonography (30%) and CT (63%-75%) for all
readers. 139 In another European study of 143 lesions, CEUS was
shown to predict malignancy with 97% sensitivity, 45% speciicity,
and 90% accuracy. CEUS was superior to CT in the staging and
characterization of RCC, as well as in the subgroup of patients
with cystic lesions. 140
he increased detection of small, incidental lesions and better
understanding of the natural history of these tumors have led
to less aggressive approaches to RCCs. he traditional surgical
approach, radical nephrectomy, is now usually reserved for larger,
central lesions. he greater likelihood of small, benign, solid
lesions in older patients 141 and the limited metastatic potential
of small (<3 cm) lesions 142 have prompted a “watchful waiting”
approach, particularly in older or ill patients. 143 Nephron-sparing
surgery (open/laparoscopic partial nephrectomy, laparoscopic
cryoablation, percutaneous radiofrequency ablation/cryoablation)
may be ofered to younger patients or older patients unwilling
or unable to undergo imaging surveillance (Fig. 9.46). Primary/
secondary eicacy and long-term survival rates with these
techniques are likely comparable to those resulting from traditional
nephrectomy. 144 Gervais et al. 145 found that radiofrequency
ablation of exophytic RCCs up to 5 cm in size can be performed
successfully. Tumors with a component in the renal sinus are
more diicult to treat. Retrospective studies have suggested that
cryoablation may be the preferred ablation modality in this
setting 146 although a recent large meta-analysis has indicated
little diference in complication rates between techniques. 147
Sonographic Appearance
Most RCCs are solid. Tumors may be hypoechoic, isoechoic, or
hyperechoic (Fig. 9.47, Video 9.2). An early ultrasound series
reported that the majority of RCCs are isoechoic (86%), whereas
the minority is hypoechoic (10%) or echogenic (4%). 148 Later
series noted the ultrasound appearance of the smaller RCCs that
are now oten depicted with cross-sectional imaging. hese smaller
RCCs (<3 cm) are oten echogenic compared with surrounding
A
B
FIG. 9.46. Ultrasound-Guided Cryoablation of Renal Cell Carcinoma. (A) Transverse sonogram shows placement of a cryoablation probe
within the posterior aspect of a small (<3 cm) echogenic renal cell carcinoma. A prior ultrasound-guided biopsy had conirmed clear cell carcinoma.
(B) Corresponding noncontrast-enhanced CT shows the ablation zone as a low attenuation “ice-ball.” Ultrasound may facilitate renal biopsy and
probe placement, although the ablation is monitored under CT.