VOL.
No.
125,
4
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MEDULLARY VISUALIZATION
RAYS*
DURING
EXCRETORY
LAWRENCE R. BIGONGIARI, HENRY APPELMAN, M.D.,
By
ANN
ARBOR,
and
MICHIGAN
M.D.,t JOHN AND
UROGRAPHY
SURESH K. PATEL, M.D., R. THORNBURY, M.D.t
CHICAGO,
ILLINOIS
ABSTRACT:
The
medullary
renal as
rays
tubules the
which
medullary
excretory and
are
form
well-defined in the
striations.
urography
anatomic
renal
cortex
These
consisting
continue
structures
in abnormal
hyperconcentration
structures
and
are
the
occasionally
renal
states
characterized
material.
Under
these
by
during
tubular
conditions,
of
medulla
visualized
physiologic
of contrast
of bundles
through
fine
stasis
striations
are
visualized which correspond in position and orientation to these structures. The work of others has shown that in tubular stasis, contrast material is hyperconcentrated in the tubules. On microradiography in normal and obstructed kidneys, the highest concentrations of contrast material are seen in the lumen of collectducts. produces
Lastly, a roentgen
ing
T
HE
medullary
tomic
urography
ducing
They
have
times
in the
recent
visualization not
illustrated
literature. first
speaking
were
in
ogy’8
standard
textbooks
knowledge, literature.
some
of
several
specific
on excretory
striation
in the
the hilus. clude that radiodense medullary the
we
situations,
the
posed
have
ducts cortex highly
our
de-
radiodensities
from
the Departments
Radiology4
produced
due rays.
of Radiologyt
Rush-Presbyterian-St.
to
of
are
clear pyramid
medullary are
and
of
Lukes
collecting
form
duct
at
the
Center,
795
of Michigan,
Chicago,
Ann
planes.
The
the
renal
the and
adjoining
is kidney,
loops the
blood
the
basic consisting
of dark
vessels
functioning of Mal-
proximal
and
papilla.
Illinois.
of the the distal
in
ducts,
to Arbor,
convoluted
distal convoluted deliver to each
several
a duct
is up
rest because and
recta.
duct,
to
The
of
corpyracom-
collecting
in all
loop of Henle, and Many nephrons
join
the are
and
striations
the
faint colored,
into
medullary B). They
randomly
corpuscle,
tubule, tubule.
University
Medical
light
Henle
the
The
the
collecting
nephron the
diameter
and Pathology,*
of and of
as vasa
pighian
contrast
of
continuations
are
shows
cortex.
substance
cut
rays
a kidney
the
projections
loops
tubules
unit
in
medullary
cut longitudinally.’6”8 appears finely granular convoluted proximal
known The
linear
radiating
of in
are
striations
Our investigation led us to conthe alternating radiolucent and stripes were produced by the rays. We then sought to prove linear
surface
medullary
Henle
have
a fine
cortex
the
ANATOMY
tex from the base mids’6 (Fig. i, A
rays we
into
rays
striated,
they
to
the medullary roentgenographically.
such circumstances are medium in the medullary From
striations
to
wish
urography renal
me-
pathol-
but,
cut
medullary
in the radiology correlation is the
radiology,
identify and
and
time;
The
pro-
in I942,’
Descriptions histology’6
for
scribe and anatomically
*
in
material cases.
NORMAL
their
described
none exists Since anatomic
foundation
of contrast our illustrated
several
When
literature
identified.
existed
Diagnostic
conditions of contrast
been
was
English
that
in
hyperconcentration
dium.
In noted
injection similar to
rays are distinct anawhich can be seen on
structures
excretory
retrograde image
of The 200j.i
collecting
Bellini
or
ducts papillary
maximum in the
Michigan,
and
external papillary the
Department
colof
Bigongiari,
796
Pate!,
Appelman ray
and is the
Thornbury center
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NORMAL
DECEMBER,
of a renal
lobule’6
1975
(Fig.
3).
PHYSIOLOGY
The physiology of contrast medium excretion has been discussed in a number of recent communications.8’9.242#{176} Only the basic principles pertinent to our discussion will be reviewed. Modern contrast media are excreted by glomerular filtration with little or no tubular secretion. The evidence is summarized by Waes.28 Therefore, the quantity of contrast medium that enters the kidney in the filtered load is the product of the plasma concentration and the glomerular
0 FIG.
I.
(A)
showing striations
continuous
Cross fine
section
striations
of in
fresh human kidney the cortex. The dark
are interlobular vessels. The light areas with the medullary striations in the
pyramid are lower pole.
medullary
rays.
(B)
Enlargement
of
lecting duct. A schematic representation of the relationships of various portions of the nephrons to the cut surface of the kidney is shown in Figure 2. As the pyramid is the center of a renal lobe, so the medullary
filtration
rate,
since
no
more
iodine will be added and none reabsorbed. The urinary system is seen on excretory urography because the iodine containing contrast material is concentrated by the kidney. The process of concentration is that of water reabsorption.”’ While several details of the mechanism are not yet known, many general conclusions have been drawn. As summarized by Valtin, water reabsorption from the renal tubules is a passive process that depends on osmotic gradients between the tubular lumen and some site within the tubular epithelium. Since Na (and Clj are normally the most abundant osmotically active particles in tubular fluid, water passively diffuses in response to an osmotic gradient set up by these ions. It has been said that 8o to 90 percent of the H20 in the filtered load is reabsorbed in the proximal tubule,9’24’26 that is, the proximal convoluted tubule (pars convoluta) and the thick portion (pars recta) of the proximal loop of Henle. The more current opinion27 is that normally no more than 70 percent of the water is removed from the filtered load in this part of the nephron. Since contrast medium is an osmotic diuretic, the amount of water reabsorbed is less than this figure, certainly not more. Nevertheless, during excretory urography the largest volume of water is reabsorbed in the proximal tubule. The cells of the proximal tubule actively reabsorb sodium, and water follows by osmosis.
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VOL.
Medullary
No.
125,
Rays
797
CAPSULE
CORTEX
MEDULLI
2. Artist’s sketch is drawn superimposed
FIG.
The
milieu
hyperosmotic
demonstrating relationship on a lobe. The medullary
of the
tubules
centrally
becomes
because
of nephrons to the cross sectional anatomy. A single lobule rays are bundles of loops of Henle and collecting ducts.
more
of the
ana-
resorption affected
tomic relationship of the loops of Henle with their hairpin turns in the medulla. Valtin27 states that countercurrent multiplication of the single effect of reabsorbing Na and Cl-, virtually without water, from ascending loops of Henle results in progressive hyperosmolality of the medullary and
makes
papillary
copapillary
osmotic aided medullary
interstitium.
The
gradient from by reabsorption portions
of
buildup
of
cortex to of urea
papilla from
the
collecting
this
is the
ducts.
In the ascending loop of Henle, solute is reabsorbed to the virtual, but not complete, exclusion of H2O. In this way, an osmotic gradient is created around the water-permeable descending loop of Henie, and since this gradient is greater centrally, a countercurrent multiplier system is formed. Water
as
up
to
the
state
by
the
tubule
kidney
will
here is
the
Water
tubular
from increase medium
that
and water,
is, the
contents
to
the
distal
the
state
corti-
water
is
with
conof the system.
distal of
duct, again the
More
the filtered load in concentration in the urinary in
on
proximal
collecting thereby
gradient.
reabsorption
is dependent
long
(vasopressin)
nephron,
osmotic
reabsorbed sequent contrast
the
hormone distal
unAs
water.
convoluted tubule more permeable to exposing
obligatory,
normal,
reabsorb
Antidiuretic the
is
of hydration.
nephron
hydration
of
the patient. While the amount of water reabsorbed in the distal nephron is small, its proportion to the tubular contents is high and
its
Pitts
effect
and
on
concentration
Valtin27
describe
is great.
the
balance
Pate!,
Bigongiari,
798
Appelman
and
Thornbury
DECEMBER,
trast medium is most structure, and since Downloaded from www.ajronline.org by 189.219.96.40 on 06/22/16 from IP address 189.219.96.40. Copyright ARRS. For personal use only; all rights reserved
physiological trast
the
reason
medium
lumen
medullary
medullary
to
of
rays,
MATERIAL
Having of anatomy
.
FIG.
Low
power
photomicrograph
of inner
for be
the
rays
concentrated there is the
we
were
no
in this known
visualized
con-
anywhere
tubules
1975
else
which conclude
but
in
form
the
that
the
visualized. AND
METHOD
concluded from our and function that
investigation the radiating
cortex
showing the medullary rays as bundles of tubular structures cut longitudinally. The renal lobules are separated by the interlobular vessels which in this specimen are packed with red blood cells. ‘S
of forces involved in glomerular filtration which separates the plasma water and nonprotein constituents from the blood cells and protein macromolecules. The glomerular arteriolar pressure is approximately 70 percent of systemic arterial pressure. This pressure is opposed by the hydrostatic pressure in Bowman’s space (within Bowman’s capsule) and by the plasma osmotic pressure in the glomerular capillary. The latter pressure tive
is exerted particles
in
the
by
the
solution
osmotically in
the
ac-
blood.
In
steady state, pressure and flow
the net result is positive of filtrate from capillary
tuft the
for
to Bowman’s driving force
space. This movement
pressure of tubular
is
fluid.
Alterations in this balance of forces can produce stagnation of tubular contents. Since the tubular contents are then exposed to the osmotic gradients for a longer period
of
time,
reabsorbed
and
trast results. radiating fine
more
cortical
observed on excretory common that they changes in function rate of tubular urine Since location, linear
the medullary shape, and striations
water
hyperconcentration The situations
(Fig.
than
usual
is
of conin which the
striations
have
been
urography have in are associated with which can reduce the flow. rays distribution 4-7),
conform to since
the
in these
con-
4. (A) Stasis nephrogram at five hours in 25 year old male with ureteral calculus. (B) Enlargement of lower pole. The fine striations in the cortex are contrast-filled medullary rays. Some can be seen extending into the medulla as medullary striations. Compare with Figure I.
FIG.
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VOL.
125,
Medullary
No.
Rays
799
fine cortical striations we observed were due to contrast medium in the bundles of tubules called medullary rays, we sought a practical, simple, and inexpensive method to reproduce this image in such a manner as to allow histologic study. Because it is unlikely that we would have the opportunity to obtain an anatomic specimen with contrast medium in the medullary rays, and because there is no simple way to identify iodinated contrast medium microscopically, we devised an indirect method. We obtained a roentgenographic image similar to that seen in our patients by retrograde ureteral injection of a normal cadaver kidney. After the ureter was
:
6. Thirty-one
FIG.
year
old
female
with
segmental
periureteral fibrosis secondary to Sansert The medullary rays are seen particularly lateral margin. cannulated
and
a mixture of
of
India
ink
pelvis.
In
was
under combinations
nous,
pyelotubular,
backflow.
This
work
tempts,
of
gentle
produced
6o injected,
fine
blood and
vessels
filling
drops the
renal
further
fluoroscopic of pyelosinus, and
tied,
several
kidneys,
hand
control obpyelove-
pyelointerstiti
al
result was expected from others.2”5 After several athand injection fortuitously
pyelotubular
strating cortex. using
hilar
various
injection tained
the
the
Conray
therapy. along the
backflow
radiating
striations
Roentgenograms a o.6 mm focal
spot
demonin
the
were obtained tube and Kodak
Industrex Type M2 Ready Pack. The specimen was cut and appropriate sections were obtained both unstained and
FIG.
5. (A)
Stasis
nephrogram
at
24
hours
in another
old male with ureteral calculus. There has been vicarious excretion of contrast medium into the gallbladder. (B) Enlargement shows medul25
lary
year
rays
more
clearly.
stained were
the
with viewed
location
hematoxyline microscopically
of the
and
India
eosin. These to determine
ink.
RESULTS
The
roentgenogram
is illustrated
(Fig.
8),
Bigongiari,
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800
Patel,
Appelman
L1 rays are well seen in this 19 was being worked up for minute delayed roentgenogram was taken for evaluation of the bladder. An excretory urogram the next day was normal with7. The year old lymphoma.
FIG.
out
medullary male who This 5
demonstration
of the
on no medication and teinuria. A transient postulated.
and
the
be
radiating
compared
fine to the
medullary
had
no
rays.
uricosuria
hypotensive
shows
rays. India
ink
pro-
is
cortical
striation
may
illustrated
cases.
Gross
High in
or
episode
and microscopic examination specimen showed black stain in lary striations extending into (Fig. 9). Unstained (Fig. ioA) sections (Fig. ioB) show India medullary
He was
power collecting
of the cut the medulthe cortex and
ink
in the (Fig.
that
radioactive
in the ureter
DECEMBER,
iodinated
pelvis would
mm et al.’9
albumin
of a kidney produce
demonstrating
1975
pyelotubular obtained
in
pelvic pressure
pressure is
There
is
elevated
back
indirect
to the why
progressively
ers5 in ureteral
Kazresults
seven
days
of
associates’3 conincrease in intra-
renal
pressure
damage, to the at
pelvic tubule.
least,
that
is transmitted
tubules. does the dense?
1966 showed obstruction using
and
evidence,
intrapelvic
But
backflow. similar
1960
causes transmitted
placed
with an obstructed “radioautographs”
after 48 hours, 72 hours obstruction. Elkin and cluded that since marked
diuresis
I i).
Thornbury
This finding corresponded with earlier clinical observations.29 A similar response occurred when the intrapelvic pressure was increased. Furthermore, increasing the blood pressure or removing the ureteral counter pressure diminished the nephrogram and filled the pelvis with contrast material. If the arterial pressure is too low or if the pressure within Bowman’s capsule and the renal tubules too high, glomerular filtration will cease and no nephrogram will be produced. Persky et al.22 in 1959 using dogs showed
stained
examination ducts
and
both
nephrogram Brenes and that with
Diodrast
during and and
become co-workacute without Hypaque,
DISCUSSION
As
a generalization,
the
medullary
rays
are visualized during excretory urography in pathophysiological states wherein tubular stasis produces hyperconcentration of contrast. Fry and Cattell’4 classify such events as producing an increasingly dense nephrogram. This phenomenon may occur in a number of conditions, all associated with changes in function which can reduce the tubular flow rate. Most common are urinary tract obstruction, hypotension, and renal vein thrombosis. In 1954, Edling and others’2 in an experimental study with rabbits showed that with fall in blood pressure to 60-70 mm Hg, filling of the pelvis by contrast medium ceases and a dense nephrogram is obtained.
8. Pyelotubular backflow produced in an autopsy specimen duplicates fine striation. A mixture of Conray 6o and India ink was injected. The specimen is lying in a puddle of contrast medium on the roentgenogram.
FIG.
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VOL.
125,
No.
Medullary
4
Rays
8oi
glomerular filtration continued. It was suggested that tubular reabsorption of water continues in the obstructed kidney decreasing the tubular hydrostatic pressure and allowing more contrast medium to enter the tubule via the glomerulus. The net effect is a steadily increasing concentration of contrast medium in the renal tubule producing a dense nephrogram. Tubular secretion of contrast medium is not necessary for this effect, since Diodrast, a contrast medium known to be excreted by tubular secretion is as effective as Hypaque, a contrast medium known to have little or no tubular secretion. Korobkin et al.2#{176} suggested that a similar mechanism occurs in the nephrogram of hypotension. The edema produced by renal vein thrombosis may also produce tubular stasis. The study of Anigstein et al.’ in 1972 using microradiographic techniques on the kidneys of rabbits and rats indicated that Hypaque is excreted in the same manner by both the obstructed and nonobstructed
FIG.
(A)
10.
showing power
Low
India view
of stained
the medullary
kidney.
power
Direct relative in both
neys.
However,
of unstained
section
section (B) Low India ink in
rays.
showing
rays.
microscopic
microradiographic
same terial
view
ink in the medullary
analysis
of
sections
showed
the
distribution normal and
of contrast obstructed
makid-
the
obstructed
kidneys
contained a greater total amount of contrast material. There was no significant amount of contrast material outside the tubular lumen in either group. The highest concentrations of Hypaque were in the lumens
--.
9. Cut
section
of specimen demonstrating Striations and
ink in the medullary
India rays.
of collecting
ducts.
In
both
groups
the concentrations were not equal in all the collecting ducts. Some showed large amounts and others little if any. This study corroborates Brenes’ hypothesis and provides anatomic correlation for our cases. Demonstration of the medullary rays on excretory urography is uncommon.
Bigongiari,
802
Patel,
Appelman
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Thornbury
striations may be seen hilus (Fig. 4B).
‘a
In his Hellmer’7
:
“/4
and
classic briefly
article noted
of
renal
periphery ing
aS
a
correlation
,‘#{149},:
4#{149}
:..
#{149}‘
#{149}
#{149}l’
a
ture also
. High
power ink
examination
showing
in a collecting
India
an
renal
vein
persisted the pattern
for
reflux
of
of the
collecting
some hours. He of alternate striation
nonopacified
individual
urine
ducts
explained
opacified
urine
We
back
up
as a function
lengths.6’7
how and possible.7
stated that is due to
He
has
why
believe may
that
an
event
reflux
part
of
is
of
the
non-
densities in their known -7).
These
ducts
or
rays the cortex anatomic
striations
further omy some
seen in polycystic
six
et
The
al.2’
In revealed.
collecting
this In of
The ducts
way some the
to (Fig. of
since
the
in
the lobular instances,
tubular
medullary
pro-
nephrogram which
in
showed
a fine
to be opacified colillustration bears a
autopsy
slender
cysts
expected
in
dissection that the disease. rays are
shows
where
specimen
of
radially
orientated
their
rays
kidney.
The
are micro-
studies of Baxter3 have shown collecting ducts are dilated in this Since we know that medullary bundles of collecting ducts, we feel to
were
visualized.
have
played due
with infantile by Lieberman
medullary
a normal
the
say
medullary
rays
Hyperconcentration some
role,
primarily
but
may visualization
to dilatatibn
R. Bigongiari,
of the
ducts.
1405
East
Ann
Arbor,
The Burr, E.
medullary
M.D.
of Radiology Hospital
Ann
Street
Michigan
radiographic R.T., Linda
Bovles,
successful
R.T.
48103
expertise Bandy, of
of
Meredith and Jane
greatly
to
R.T.,
contributed
outcome
the
the
experimental
studies.
anat-
portion the
can article
caused by tubular Coel and Tamer’0
believed Their
case
Department University
linear
groups
ducts,
litera-
Tamm-Horsfall
of 14 patients disease reported
illustrated
was
collecting duct is well power of conventional
visualization is obtained.
either
dilated
size of the normal below the resolving
as
corresponding distribution are
individual
roentgenography. anatomy is
appear
the
striation to an
striking resemblance to our Figure 4. A similar radial fine cortical striation corresponding in location, arrangement, and distribution to the medullary rays was
Lawrence medullary
of
entire
explanation. The
lecting
surface
in
obstructive
it appropriate
demonstrated
such
be
some
of their
on
thrombosis they ducts.
striation
Whether or not they are visualized depends on the degree and extent of tubular stasis. This phenomenon probably occurs more often than is realized, since it usually occurs after the standard examination is completed. Bretland6 noted alternate striation in six of his 86 cases of acute ureteric obstruction followed closely until the affected kidney was shown to excrete. He also noted the similarity of the distribution to the medullary rays. The striation appeared after the delayed nephrogram had
correspondcut
appeared
probably by casts.
illustrated
duct.
not
It was
obstruction
-
I I
shadow of the
et al.4
Berdon
the
experiments show these rays. A more complete
has
teinuria.
toward
on the nephrogram, fine striations at the
since that time. This fine be seen in an illustration
by
FIG.
the
1975
radiating
appearance
the kidney. Our to be the medullary
1,S
a,
the
to
DECEMBER,
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ELKIN,
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VoL.
125,
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No.
radiographic
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Radiol.,
Rays
7,
1972,
24-32.
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children: morphology, distribution tion of cysts. Nephron., 1965, 2, BERDON, W. E., SCHWARTZ, R. H.,
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TALNER,
uremia. 421-432. 27.
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7. Radiol.,
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oliguric 1972. WICKBOM, 1-5.
and I.
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