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,

REFERENCES

of

R.,

I. ANIGSTEIN, SCHULZ,

R.

ELKIN,

J. Obstructive

M.,

ROLAND,

nephrogram:

P., and micro-

VoL.

125,

Medullary

No.

radiographic

studies.

Invest.

Radiol.,

Rays

7,

1972,

24-32.

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2.

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D. Pyelorenal

BAUER,

GENOL.,

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78, 296-316. T. J. Polycystic

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4.

children: morphology, distribution tion of cysts. Nephron., 1965, 2, BERDON, W. E., SCHWARTZ, R. H.,

D.

BAKER,

kidney

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of infants

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Radiology, 1969, BRENES, L. G., FORLANO, N., and STAJJFFER, H.

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P.

M.

COEL,

N.,

and due

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714-722.

H., M.

KOUTOURATSAS,

SPENCER,

Excretion 6i-8o.

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FRY,

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experimental

7. Urol.,

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KIRKWOOD,

Nephrogram 98, 129-133.

of

LIEBERMAN, E., SALINAS-MADRIGAL, L., GWINN, J. L., BRENNAN, L. P., FINE, R. N., and LANDING, B. H. Infantile polycystic disease of

hepatic L.,

PERSKY,

BONTE,

of backflow

Pn-rs,

fibrosis.

and with

Medicine,

F. J., and hydronephrosis:

1971,50,

G.

AUSTEN, radioauto-

7. Urol.,

patterns.

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of the Kidney and Body Publishers, Inc., Chicago,

R. F. Physiology

Fluids. 24.

Book

Year

J.,

and

25.

26.

L.

TALNER,

uremia. 421-432. 27.

studies.

Brit.

and

FRENCH,

S.

7. Radiol.,

Brit. of

intravenous

Med.

Brown

Function:

and

A.

urog-

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WAES,

29.

oliguric 1972. WICKBOM, 1-5.

and I.

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Medullary rays. Visualization during excretory urography.

The medullary rays are well-defined anatomic structures consisting of bundles of renal tubules which form in the renal cortex and continue through the...
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