AJR 2005; 184:S104-S106
© American Roentgen Ray Society
Renal Cell Carcinoma Visible Only During the Corticomedullary Phase of Enhancement
Edward Y. Lee1,2,
Jay P. Heiken1,
Phyllis C. Huettner3 and
Wittanee Na-ChiangMai1,4
1 Mallinckrodt Institute of Radiology, Washington University School of Medicine,
510 S Kingshighway Blvd., St. Louis, MO 63110.
2 Department of Radiology, Children's Hospital Boston and Harvard Medical
School, 300 Longwood Ave., Boston MA 02115.
3 Lauren V. Ackerman Laboratory of Surgical Pathology, Washington University
Medical Center, St. Louis, MO 63110.
4 Present address: Department of Radiology, Faculty of Medicine, ChiangMai
University, ChiangMai 50200, Thailand.
Received March 15, 2004;
accepted after revision April 28, 2004.
Address correspondence to E. Y. Lee
(Edward.Lee{at}childrens.harvard.edu).
Introduction
Renal cell carcinoma is the most common primary malignant neoplasm
of the kidney. In the United States in 2002, more than 31,000 patients were
diagnosed with renal cell carcinoma, and more than 11,000 patients died of
their disease [1]. Early
detection of renal cell carcinoma is critical because smaller and lower-stage
renal cell carcinomas are more likely to be cured by surgical resection
[2]. Helical CT is currently
the standard imaging test used to detect and stage renal cell carcinoma. The
nephrographic phase of enhancement has been emphasized as the critical phase
for tumor detection. We present a case of renal cell carcinoma in which the
tumor was seen only during the corticomedullary phase and not during the
nephrographic phase of enhancement, which emphasizes the importance of
multiphase imaging in the evaluation of a patient with suspected small renal
cell carcinoma.
Case Report
A 69-year-old man with medical history significant for lumbar spine hernia
repair presented to the emergency department with new onset of cramping left
upper quadrant pain of several days' duration. The findings at physical
examination were unremarkable except for mild left flank tenderness on deep
palpation. The laboratory examination, including urinalysis, yielded results
within the normal limits except for a mild elevation of serum amylase.
The patient underwent a multiphase CT examination of the abdomen and pelvis
on a single-detector scanner (Somatom Plus 4, Siemens Medical Solutions)
before and after administration of IV contrast material. No oral contrast
medium was administered. First, an unenhanced CT examination of the abdomen
and pelvis was performed. The patient then received 125 mL of iodinated IV
contrast material (Optiray 350 [ioversol], Mallinckrodt) at an injection rate
of 3 mL/sec. Contrast-enhanced images were obtained at 30 sec
(corticomedullary phase) and 100 sec (nephrographic phase) after the
initiation of contrast medium administration.
The CT examination showed a hypervascular mass that was 1.0 cm in diameter
and was located in the mid to lower left kidney. This renal mass was
visualized only during the corticomedullary phase of the examination
(Fig. 1A). The mass was
isoattenuating with the normal renal parenchyma on the unenhanced images
(Fig. 1B) and during the
nephrographic phase of enhancement (Fig.
1C). Neither lymphadenopathy nor renal vein involvement was
present.
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Fig. 1A. —69-year-old man with left renal mass. Hypervascular renal
cell carcinoma (arrow) measuring approximately 1.0 cm in diameter is
conspicuous on this helical CT image obtained during corticomedullary phase of
renal parenchymal enhancement.
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The patient subsequently underwent a partial left nephrectomy. A
red-yellow, lobulated mass measuring 1.0 cm in its greatest dimension was
identified on gross examination. Histologic sections showed renal cell
carcinoma, clear cell type, Fuhrman nuclear grade 2 of 4. The sections were
characterized by nests and sheets of tumor cells with abundant clear cytoplasm
and mildly pleomorphic nucleoli with nucleoli
(Fig. 1D). No lymphovascular
space invasion was identified. The inked resection margin was free of renal
cell carcinoma. No renal capsule, renal pelvis, ureter, or lymph nodes were
present in the specimen.
The patient's postoperative course was uneventful. Five years after
undergoing surgery, the patient is currently doing well without evidence of
tumor recurrence.
Discussion
Renal cell carcinoma accounts for approximately 2% of all malignancies and
is the most common primary malignancy of the kidney
[1,
2]. It originates in the renal
cortex and constitutes approximately 80-85% of malignant renal neoplasms
[3]. Renal cell carcinomas
generally are classified into six subtypes: clear cell, papillary
(chromophil), chromophobe, collecting duct, medullary, and unclassified
carcinomas [3]. Among these,
the clear cell subtype of renal cell carcinoma is the most common, accounting
for approximately 75-85% of all renal cell tumors
[3]. The most important
prognostic factors for patients with renal cell carcinoma are the stage of the
disease at diagnosis and the nuclear grade. The tumor is more likely to be
cured by surgical resection when it is small and of low stage. Thus, early
detection of renal cell carcinoma is crucial for improving the survival rate
from this disease.
Among the many imaging tests currently available for diagnosing renal cell
carcinoma including excretory urography, sonography, CT, and MRI, CT is widely
considered the imaging test of choice for detection and staging. For tumors 3
cm in diameter or smaller, the sensitivity of renal tumor detection is 67%
with excretory urography, 79% with sonography, and 95% with helical CT
[3]. State-of-the-art
contrast-enhanced MRI is comparable to helical CT for detection, diagnosis,
and staging of renal masses
[2]. However, CT has the
advantages of widespread availability, shorter examination time, and lower
cost in comparison with MRI
[2].
The widespread use of helical CT for abdominal imaging has led to earlier
discovery of many small renal neoplasms. Compared with conventional CT,
helical CT has improved the diagnosis of renal masses by decreasing the
potential limitations of partial volume averaging and respiratory
misregistration [2].
Furthermore, because of its rapid scanning time, helical CT enables image
acquisition during multiple phases of renal parenchymal enhancement after IV
contrast medium administration.
Currently, the CT technique recommended for detection and staging of renal
cell carcinoma is a multiphase protocol, which includes unenhanced CT followed
by corticomedullary and nephrographic phase imaging of the kidneys
[2,
4-7].
The unenhanced images provide a baseline for measuring enhancement of the
lesion after IV contrast medium administration. The corticomedullary phase is
the first phase of renal parenchymal contrast enhancement, occurring between
25 and 70 sec after the start of the contrast medium injection
[4]. During this phase, the
brightly enhancing renal cortex can be easily differentiated from the
minimally enhancing renal medulla
[4]. The nephrographic phase is
best imaged after a scanning delay of at least 80 sec and lasts up to 180 sec
after the start of contrast medium injection. During the nephrographic phase,
the renal parenchyma enhances homogeneously, providing the best opportunity to
discriminate between the normal renal medulla and masses
[4].
Multiple studies have shown that the nephrographic phase of enhancement is
more sensitive than the corticomedullary phase for tumor detection
[5-7],
although the corticomedullary phase is considered essential for staging
[2,
4]. The authors of these
studies have emphasized the limitation of corticomedullary phase imaging for
the detection of small renal lesions
[5,
6]. Occasionally, a
hypervascular renal cell carcinoma may enhance to the same degree as the renal
cortex on corticomedullary phase images and be mistaken for normal parenchyma.
Conversely, a hypovascular renal cell carcinoma may be mistaken for unenhanced
renal medulla during the corticomedullary phase and therefore may be missed
[8]. The authors of a
comprehensive review of the different phases of renal enhancement during
helical CT stated that, to their knowledge, no instance of a renal tumor
missed on nephrographic or excretory phase images but identified on
corticomedullary phase images has been reported
[8]. We also are unaware of any
such case reported before this one.
Contrary to the conclusions gleaned from prior studies, our case shows
that, on occasion, renal cell carcinoma may be detectable during the
corticomedullary phase of renal parenchymal enhancement, but it may be
difficult to identify during the nephrographic phase. The lack of
conspicuousness of the mass on the nephrographic phase images may be due to
the fact that some hypervascular renal cell carcinomas may equilibrate in
attenuation value with the rest of the renal parenchyma during the
nephrographic phase of the CT examination. Admittedly, this is a relatively
rare occurrence. Nevertheless, it underscores the recommendation of previous
authors that for optimal evaluation of a known or suspected renal mass,
multiphase imaging is required
[4,
5,
7]. The corticomedullary phase
is therefore essential not only for staging but also, on occasion, for
detection of renal cell carcinomas. In cases such as the one we describe, the
use of a narrow window setting may help to accentuate a very small difference
in nephrographic phase attenuation value between a renal cell carcinoma and
the surrounding renal parenchyma.
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Introduction
Case Report
