Key words
abdomen - MR-imaging - contrast agents
Introduction
Contrast-enhanced abdominal MRI is routinely used in diagnosing pediatric patients
with all types of abdominal diseases. It is used in particular in the diagnosis and
follow-up of both tumors and non-malignant diseases.
The cortical region of the renal parenchyma generally exhibits homogenous contrast
following the administration of gadolinium. In individual cases, however, we have
incidentally observed an unusually striated image in late phase contrast-enhanced
images. As this phenomenon has not yet been explicitly described in scientific MRI
literature, this retrospective article examines how frequently and in which clinical
context striated MRI nephrograms appear in pediatric cases.
Material and methods
Altogether, 855 contrast-enhanced MRIs performed over 362 patients (180 females, 182
males, ages 0 – 18) between July 2006 and May 204 were evaluated. Of the 362 patients,
136 were examined for suspected tumors or to evaluate the course of known tumors,
accounting for a total of 565 of the 855 examinations. The examinations were performed
on a 1.5- (Intera, Philips; Amsterdam, Netherlands) and a 3-Tesla machine (Siemens
Trio, Siemens Healthcare, Erlangen, Germany) using the contrast medium Omniscan® (GE Healthcare, Chalfont St Giles, U.K.), Dotarem® (Guerbet, Villepinte, France), Gadovist® (Bayer Schering Pharma AG, Berlin, Germany) und Multihance® (Bracco Diagnostics, Milan, Italy), which were administered intravenously according
to weight (0.2 ml per kg of body weight) (or 0.1 ml per kg of body weight in the case
of Gadovist). Depending on the clinical objective, either dynamic or non-dynamic sequences
were performed following the administration of contrast agent. If a striated nephrogram
was yielded, the following information was documented in addition to the underlying
disease: the current medical history, the glomerular filtration rate (based on plasma
creatine using the Schwartz formula) as kidney function marker, the contrast medium
used and the respective dose as well as the time between administering contrast medium
and the appearance of the striated nephrogram. All examinations were evaluated by
a radiologist (S.S.) with four years' experience in MRI. Positive reports were evaluated
by a second radiologist (F.W.H.) with 20 years’ experience. If there was a discrepancy
between the radiologists’ evaluations, final assessment was reached through consensus.
Results
A striated nephrogram was found in a total of 9 patients ([Table 1]), 5 males and 4 females, and in 11 examinations (3 positives for 1 patient), corresponding
to a frequency of 1.3 % ([Fig. 1], [2]). The patients were children with different underlying diseases: 7 children were
undergoing tumor assessment following chemotherapy (5 neuroblastomas as well as 1
contralateral nephroblastoma), accounting for 1.1 % of all abdominal MRI examinations
following administration of contrast medium. At the time of examination, two of these
patients were in the midst of ongoing chemotherapy. For the remaining patients, the
time span between their last chemotherapy and the MRI ranged between 7 months and
4 years. In addition, two of the children exhibiting remarkable nephrograms had no
prior tumors and had not received chemotherapy or any other type of long-term therapy.
One child had a venous malformation, while the other had a hepatic cyst. This accounted
for 0.2 % of all abdominal MRI examinations following administration of contrast medium.
Table 1
Patients with striated nephrogram.
|
pat. no.
|
age [in years]
|
underlying disease
|
kidney function and urine status
|
time following administration of contrast medium [in minutes]
|
contrast medium and dosage [in ml]
|
|
1
|
5
|
neuroblastoma stage I
|
n.p.
|
10
|
Dotarem; 4
|
|
2
|
2
|
neuroblastoma stage IV
|
n.p.
|
16
|
Dotarem; 3
|
|
3
|
7
|
neuroblastoma stage I
|
n.p.
|
29
|
Dotarem; 4
|
|
4
|
1
|
hepatic cyst
|
n.p.
|
13
|
Dotarem; 2
|
|
5
|
4
|
nephroblastoma
|
n.p.
|
38, 9, 13
|
Dotarem; 6
|
|
6
|
8
|
neuroblastoma stage IV
|
n.p.
|
11
|
Omniscan; 15
|
|
7
|
6
|
neuroblastoma stage IV
|
n.p.
|
23
|
Dotarem; 4
|
|
8
|
4
|
venous malformation
|
n.p.
|
15
|
Dotarem; 4
|
|
9
|
2
|
hepatoblastoma
|
n.p.
|
16
|
Gadovist; 2
|
Pat. no. = patient number, min = minutes, ml = milliliter, n.p. = not pathological.
Fig. 1 Sample image of a striated nephrogram in a fat-saturated T1 spin echo sequence following
administration of contrast medium in axial view.
Fig. 2 Sample image of a striated nephrogram in a fat-saturated T1 spin echo sequence following
administration of contrast medium in coronal view.
At the time of examination, none of our patients exhibited impaired kidney function
in terms of estimated glomerular filtration rate or infectious kidney disease.
The span of time between the administration of contrast medium and the appearance
of the striated nephrogram ranged between 9 and 38 minutes with a median of 17.5 minutes.
The contrast medium Dotarem® (Guerbet, Villepinte, France), was administered for 7 patients, Omniscan® (GE Healthcare, Chalfont St Giles, UK) for 1 patient and Gadovist® (Bayer Schering Pharma AG, Berlin, Germany) for 1 patient as well, with Dotarem being
used for a total of 512, Multihance for 30, Omniscan for 98 and Gadovist for 215 examinations.
All striated nephrograms were observed exclusively with examinations performed on
the 3-Tesla machine (Siemens Trio, Siemens Healthcare, Erlangen, Germany), which was
used for 578 of the 855 examinations.
Discussion
Changes in the renal parenchyma, which normally exhibits homogenous contrast, have
been described following the administration of contrast medium in CT examinations
for various kidney diseases [1]. This unilateral or bilateral striated nephrogram seen on CT has been attributed
to obstructive uropathy as well as renal vein thrombosis, trauma, arterial hypotension
and acute cases of pyelonephritis [1]. In terms of their etiology, these changes in nephrogram involving remarkable striation
following the administration of contrast medium were associated with a displacement
of the renal tubules, e. g. resulting from the precipitation of proteins, with this
finding initially being described in 1971 among patients with multiple myeloma [2]. However, other substrates such as, for example, Tamm-Horsfall-proteins, uric acid,
myoglobin in the case of rhabdomyolysis or dehydration have also been accepted as
causal [1]
[3]
[4]
[5]
[6], a displacement of the tubules with consecutive stasis of the contrast medium having
been discussed on the etiopathological level as a cause of the appearance of a striated
nephrogram.
Although these striated signal decreases in MR nephrograms are likewise familiar to
several radiologists, this phenomenon has not yet been addressed in scientific radiological
literature on magnetic resonance imaging.
Because it was remarkable that there was a relatively long span of time between contrast
medium being applied and the striated nephrogram appearing, the author's posit that
the striated, signal-free zones in the renal parenchyma are possibly an accumulation
of contrast medium and a contrast inversion resulting from an intensified T2 shortening
effect when a very high gadolinium concentration is present, with the striated appearance
being explained by the tubular structure of the tubules as they run from the renal
cortex to the renal papilla.
This phenomenon observed more frequently in patients following chemotherapy may be
caused by a stasis of the contrast medium in the tubules following prior chemotherapy,
e. g. through damage thereto or through intraluminal deposits. However, because the
same phenomenon was also visible in two cases in which we were unable to see a causal
connection to a prior or acute disease, the striated nephrogram may also constitute
an incidental, non-pathological finding in these cases. Supporting a non-pathological
finding are also the facts that the striated nephrograms yielded for the patients
in question were not replicated in the subsequent follow-up examinations and that
the phenomenon appeared only in examinations performed on the 3-Tesla machine, implying
a dependency on field strength. Arguing against this are the results of Trout et al.
[7], who examined the same phenomenon and demonstrated an association between the appearance
of a striated nephrogram and a specific MR scanner regardless of field strength. However,
this study likewise concedes an absent causal pathology.
One limitation of the present study is that it is a retrospective assessment, thus
meaning that the follow-up observation period was not of comparable length for all
patients. If comparably long follow-up observation periods were employed, it would
have to be assumed that the incidence of this incidental finding could increase. Another
limitation was that different MR contrast media and non-uniform examination protocols
were used.
Conclusion
Unlike in CT examinations, where it has been described only in connection with an
underlying pathology, a remarkable striated nephrogram in the late phase of an MRI
examination following the administration of contrast medium appears to occur as an
incidental finding following the intravenous administration of contrast medium and
presumably involves an intensified T2 shortening effect resulting from a high concentration
of contrast media in the renal tubules, which is demonstrated particularly at a field
strength of 3 Tesla, with presumably no pathological significance being attached to
this finding.
