Anatomic Communications Between the Three ...

1173

Anatomic Between Spaces:

Communications the Three Retroperitoneal Determination by CT-Guided of Contrast Material in Cadavers

Injections

Howard J. MindeII1 F. Mastromatteo1 Kevin W. Dickey2 Norman V. Sturtevant William P. Shuman1 Christina L. Oliver1 Karen L. Leister1 Richard A. Barth3

James

OBJECTIVE. and trauma

A variety

may cause

of retroperitoneal

fluid collections

purpose of our study was to elucidate partments to assist the clinical-radiologic peritoneal

diseases

in the three

such as pancreatitis,

infection,

major

retroperitoneal spaces. The of fluid between the various com-

flow patterns assessment

and treatment

of various

retro-

diseases.

MATERIALS AND METHODS. In eight cadavers, CT guidance was used to selectively inject 35-1000 ml of contrast medium by hand or power injector into five perirenal, two posterior pararenal, and two anterior pararenal spaces. After the injections, CT of the entire abdomen and pelvis was done with 10-mm-thick sections at intervals of 10-40 mm. All images were reviewed in detail by a group of experienced body imagers to assess the pathways of flow of contrast material between the three major retroperitoneal spaces. RESULTS. The caudal cone of perirenal fascia was uniformly patent. A narrow channd connected the two perirenal spaces in the midline; the posterior border of this channel abutted the anterior margins of the abdominal aorta and the inferior vena cava. The perirenal, anterior pararenal, and posterior pararenal spaces all communicated with the infrarenal space, which in turn connected with the extraperitoneal

spaces in the pelvis. When large quantities

of contrast

renal or panarenal spaces and the infranenal then serve as a conduit across the midline

medium

are injected in the

pen-

space is filled, the infrarenal space may of the abdomen. The anterior paranenal

space crossed the midline and had a distinct retnorenal extension but no intrapenitoneal connection. The slender posterior pararenal space had an antenolateral extension en route

to the pnevesical

CONCLUSION. nor

pararenal,

space.

Our findings and

posterior

show pathways panarenal

and extensions

spaces

assessing a variety of retnopenitoneal diseases. hematomas and uninomas, have at least a potential the pelvis.

Our study

explains

may enter either peninephnic

how blood

from

space. Anterior

that

Received December6,

April 1 4, 1994; accepted 1994.

1 Department of Radiology, Radiology Health Care Service, Medical Center Campus, Fletcher Allen Health Care, 111 Colchester Ave., Burlington, VT 05401 . Address correspondence to H. J. Mindell.

2Department of Radiology, Yale-New Haven Hospital, 20 York St. , New Haven, CT 06504. 3Department of Radiology, S-056, Stanford University

Medical

Center,

© American

Roentgen

Stanford, 73

Ray Society

ante-

be considered

when

a ruptured

pararenal

abdominal

processes, the midline,

aortic

aneurysm

such as pancreatiand posterior

para-

1995;164:1173-1178

after revision

Presented at the annual meetings of the Society of Uroradiology, Laguna Niguel, CA, January 1994, and the American Roentgen Ray Society, New Orleans, LA, April 1994.

0361-803X195/1645-11

of the penirenal,

Peninephnic collections, such as conduit across the midline or into

tis or appendicitis, can extend into the pelvis or cross renal blood from trauma can also flow into the pelvis. AJR

should

CA 94305-5105.

Our understanding of the communications between the retroperitoneal spaces has been derived largely from imaging observations in various clinical settings [1] such as pancreatitis. Experimental studies [2-8] have included CT correlations with cross-sectional cadaveric anatomy, dissections, and plain film radiography after injections of various contrast agents. Concepts regarding the extraperitoneal spaces are comprehensively analyzed in the treatise by Korobkin et al. [9], who note that many uncertainties persist in this area. A clear understanding of the communications between the major retroperitoneal spaces is vital in evaluating and treating many retroperitoneal disorders, especially where fluid collections are involved. To this end, we mapped these communications in cadavers, using CT-guided injections of water-soluble contrast medium, the viscosity of which simulates that of many pathologic effusions. To our knowledge, this is the first systematic study of these anatomic communications.

1174

MINDELL

Materials

and Methods

Nine cadavers and unembalmed. mens be used for made their entire individual individuals tion,

were

tissue

ment.

were more

planes,

These

femoral

artery,

solution

via femoral

from

the

thawed and

and

ease

artery

for 24 hr before

aortic

CT guidance space the

or in the first

lack

anterior

240-1000

ml of contrast

rate

mI/sec.

of 0.5

thick

sections 1 0-40

ally

except

needle

were

included

To correlate

spaces

data

injected,

or supine),

space

the

and

CT

either

pararenal

second

was

intervals

between sagittal

from

six

used,

slices

and

35 or 50 ml of

by power were

or supine,

CT scans

studies,

instilled

disease;

of emaciation

subsequent

studies,

injector

at a

with

10-mm-

as needed,

gener-

reconstruction

of a perirenal

medium were added to the so the entire abdomen and

as needed. and

illustrations

we tabulated injected,

from

information and

total

the

various

by cadaver,

volume

cadavers

approach

of contrast

medium

and

(prone per

space, as follows. Five perirenal spaces were injected in four prone cadavers: 35 ml of contrast medium into the right in one, 50 ml bilater-

Fig. 1.-Perirenal

space and communication

of contrast

Two

1000

posterior

ml into the

pararenal

left in one,

spaces

were

and

240

ml into the

right

in two prone

injected

May 1995

in one.

cadavers:

500 ml into the left in one and 300 ml into the left in the other. Two anterior pararenal spaces were injected in two supine cadavers: 400 ml into the

left in one

A group of body

four

imagers)

image

in

and

met

detail,

arriving

Requirements

included that

(a at

clear

injections

compartment.

The

ways

the spaces.

between

ml into the

conjointly

scout

sections

900

radiologists

study

and

and

CT

three

reviewed

consensus were

group

left in the other.

resident

on

each all

documentation made

focused

precisely on

experienced injection

and

data

generated.

with

appropriate

into

the

reproducibility

desired of path-

available

with a known

prone

space.

third

techniques

instance,

were

then

in the perirenal

because

In the

drainage and

abdominal

localization

usable

injected.

fluid

for one cadaver

space was done. As aliquots of contrast various spaces, scanning was repeated, pelvis

placeinto

frozen

records

the cadavers

material

variable in one

accurate

instillation

were

Clinical

not

Standard

and mm;

were hand

Larger

fat distribu-

simultaneous

for preexisting

With

In the

was

for

with

cadavers

CT study.

or posterior

planes.

material

access

with The

precise

studied

of tissue

contrast

vein.

aneurysm.

cadaver

retroperitoneal

of size.

of 24 I of a phenol-formaldehyde-alcohol

disease

permitted

better prepared

screened

none had retroperitoneal

on the basis

of needle been

each

were

mainly

cutdown,

femoral

all specimens

with

had

over 3 days,

ipsilateral

abdominal

selected

suitable,

cadavers

AJR:164,

ally in one,

were studied. The first two specimens were fresh Logistic constraints required that embalmed specithe remainder of the study. The anatomy laboratory collection of cadavers available for our study, and

specimens

ET AL.

medium

Results Perirenal

Space

When the kidney was used as a marker, the perirenal space was easy to target in five spaces in four cadavers because of its large size (Fig. 1A). The injected contrast material readily escaped from the inferior cone of renal fascia caudally in all five cases, even with small amounts of contrast material (50 ml) injected into the space described by Korobkin et al. [9] as the infrarenal space (Figs. 1 B and 1 C). Even when 50 ml of contrast material was injected into the perirenal space, the contrast material flowed into the ipsilateral side of the pelvis (Fig. 1 D). With larger amounts of contrast material, flow occurred from the perirenal space to the infrarenal space and then to the extraperitoneal spaces in the pelvis. With 200 ml of contrast medium in the perirenal space, contrast medium flowed across the midline via a channel connecting the two perirenal spaces (Fig. 2). In one

from this space via perforate

cone of caudal perirenal

fascia into infrarenal

space

and extraperitoneal spaces in pelvis. A, CT scan of prone cadaver after injection of 50 ml of contrast medium into left perirenal space (black arrow) shows contrast material abutting renal margin (white arrows). This illustration confirms injection was in perirenal space prior to demonstration of communication of this space in B, C, and 0. B, CT scan of prone cadaver after injection of 50 ml of contrast medium into left perirenal space shows contrast medium (arrow) on psoas muscle well down in pelvis at level of iliac crests (IC), proving inferior cone of renal fascia is open. C, Sagittal reconstruction of images from A and B, same injection, showing kidney (K), perirenal space posterior to kidney (P), and iliac crest (IC). Split Image shows slightly different planes: left image through midplane of kidney, right image slightly more medial. These reconstructions again prove patency of inferior cone of renal fascia, permitting exit of contrast material down to level of iliac crest into infrarenal space (I). 0, CT scan of prone cadaver after 50 ml of contrast material was injected into left perirenal space shows contrast medium (arrow) in pelvis at level of sacrum (double arrows), proving that contrast medium extends from perirenal space into pelvis at level of caudal end of infrarenal space.

AJA:164,

CT

May 1995

OF

RETROPERITONEAL

cadaver, a large abdominal aortic aneurysm appeared to prevent even 240 ml of contrast medium in the perirenal space from crossing the midline. More caudally, however, in the same cadaver, the contrast medium crossed the midline anterior to the bifurcating iliac vessels (Fig. 3). Posterior

Pararenal

Space

This smaller, organ-free potential space was identified and then injected with more difficulty (Fig. 4A and 4B). No direct communication between the posterior pararenal space and the perirenal space or the anterior pararenal space was shown, but when larger volumes of contrast material were injected, flow was noted laterally and anteriorly, surrounding the inferior tip of the perirenal fat and proceeding laterally to the lateroconal fascia (Fig. 4C). The posterior pararenal space also connected with the infrarenal space, and 300 ml of contrast material flowed from the infrarenal space toward the prevesical space anteriorly (Fig. 4D). In a second cadaver with 300 ml of contrast medium in the posterior pararenal space, a connection to the infrarenal space and then across the midline was noted. Anterior

Pararenal

Space

posed of dense fibrous sheets that are not ordinarily friable. Water-soluble contrast media more closely simulate pathologic effusions than do barium mixtures [6-8] or latex [7, 11] used in other studies. Pathologic effusions may behave differently than contrast media. No dissections were done to confirm the CT findings because the dissections themselves would distort the anatomic pathways between the retroperitoneal spaces. CT scans made after CT-controlled injections of contrast medium provide a unique opportunity to determine the anatomic communications that exist between these spaces. Many of the spaces studied are filled with fat and/or traversed by fibrous septa. For instance, contrast medium in the perirenal space typically surrounds the renal vessels medially, but the flow is limited laterally by fibrous strands running through this space (Fig. 1). Also, normal tissue planes may be disrupted when large volumes of contrast medium are used. However, similar flow patterns encountered in different cadavers makes this unlikely. Finally, only left-side injections were done in the anterior and posterior pararenal spaces. It is possible that pathways or anatomic appearances are not identical on both sides. Clinical

The anterior pararenal space was the most difficult space to inject with contrast material because it was collapsed. The pancreas was used as our marker for needle localization because the space is central. Contrast medium injected via the left anterior approach (Fig. 5A) surrounds the tail of the pancreas and then (Fig. SB) outlines Gerota’s fascia and tracks retrorenally. With large amounts of contrast medium in the anterior pararenal space (Fig. SC), the contrast reaches the extraperitoneal spaces in the pelvis via the prevesical space, crosses the midline to surround the pancreas (Fig. 6A), and fills the infrarenal space from which the extraperitoneal spaces in the pelvis fill (Fig. 6B).

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SPACES

Relevance

A variety

of retroperitoneal

diseases

may

cause

fluid

pro-

duction or accumulation, and our results can help in the clinical and imaging evaluation of such fluid and its extensions or communications. Pancreatitis, appendicitis, and diverticulitis mainly involve the anterior pararenal space. Urinomas, penrenal abscesses, and leaking abdominal aortic aneurysms mainly involve the penirenal spaces. Fluid or hemorrhage from trauma may affect any of the three retropenitoneal spaces. We showed communications from the extrapenitoneal spaces in the pelvis that could permit, for instance, fluid from retropenitoneal bladder rupture to extend into the abdominal retroperitoneal spaces. Conversely, collections related to appendicitis might track down into the pelvis.

Discussion Technical

Limitations

of the Study

It is unlikely that tissue planes were disrupted by standard preparation of the cadavers in the anatomy laboratory. Disruption has not been encountered in previous similar studies [7, 1 0, 11]; moreover, the fascial planes involved are com-

Fig. 2.-Potential midline communication of perirenal spaces. CT scan of prone cadaver aftar 200 ml of contrast medium was injected into right perirenal space (large single arrow) to show narrow channel crossing midline (double arrows) that may connect penirenal spaces, as it sits anterior to inferior vena cava (small arrow) and aorta (arrowhead). K = kidney.

Fig. 3.-Fluid in perirenal space may cross midline via infrarenal space. CT scan of prone cadaverafteninjectlon of240 mlofcontrast medium

Into right perlrenal

space shows that with large

volumes of contrast material, (large arrow) may cross midline

Infrarenal space (small arrow).

Perirenal

Spaces

Korobkin et al. [9] noted “discrepant results of anatomic and radiologic studies” and raised questions about the patency of the penirenal spaces medially and infenionly. Although historical consensus had suggested medial closure

1176

MINDELL

ET AL.

AJR:164,

Fig. 4.-Anterolateral

of posterior

pararenal

.

:

B

A

space shows location

of contrast

ma-

tenial in posterior pararenal space (small arrow) and its anterolateral extension (large arrow). C, CT scan of prone cadaver after 220 ml of contrast medium was Injected into left posterior pararenal space shows anterolateral extension of space (arrow) to level of left iliac crest (IC). 0, CT scan of prone cadaver after 300 ml of contrast medium was injected into left posterior pararenal space shows its connection with infrarenal space (small arrow) and Its extension anterolaterally (large arrow) en route to prevesical space.

J1v ,

1995

pararenal space, Its relation to anterior pararenal space, and its communications to extraperitoneal spaces in pelvis. A, Localizer CT scan of left posterior pararenal space in prone cadaver shows needle clearly placed a few millimeters from posterior renal fascia (arrow). This scan shows precision that can be achieved when injecting retroperitoneal spaces with CT guidance. B, CT scan of prone cadaver after 1 00 ml of contrast medium was injected into left posterior

‘V r’,.

extension

May

B Fig. 5.-Anterior

pararenal

space, its retrorenal

extension,

and route toward

prevesical

space.

A, CT scan of supine cadaver after 30 ml of contrast medium was injected into left side of anterior pararenal space shows needle tip localized to margin of pancreatic tail (P = pancreas) and slender track of contrast medium in anterior pararenal space (arrow) bordering perirenal space (double arrow). B, CT scan of supine cadaver after 1 20 ml of contrast medium was injected Into anterior pararenal space shows retrorenal extension of space (small arrow). Note contrast material (large arrow) that leaked retrogradely around needle track into lesser sac; no intraperltoneal extension of anterior pararenal space was seen otherwise. C, CT scan of supine cadaver after 400 ml of contrast medium was injected into anterior pararenal space at level of femoral head (FH) shows how anterior pararenal space can also track down (arrow) posterior to transversalis fascia en route to prevesical space.

of the penirenal spaces, Kneeland et al. [1 0] used selected CT scans of two cadavers after selective injections of contrast medium or water into the penirenal spaces to show a

midline communicating channel. We confirm the existence of Kneeland’s narrow channel that may connect the two perirenal spaces (Fig. 7A), although this channel may be obstructed by

AJA:164,

May 1995

CT OF

RETROPERITONEAL

SPACES

1177

Fig. 6.-Anterior pararenal space relates to retroperitoneal colon and communicates to cxtraperitoneal spaces in pelvis. A, CT scan of supine patient after 180 ml of contrast medium was injected into anterior pararenal space and surrounded pancreas (black arrows = posterior pancreatic margin) shows retrorenal extension (thick white arrow) between two layers of posterior renal fascia and how anterior pararenal space is related to descending colon (thin white arrow). B, CT scan of supine cadaver after 900 ml of contrast medium was injected into anterior pararenal space shows communications down to extraperitoneal spaces in pelvIs, including prevesical (thin white arrow), perivesical (thick white arrow), and presacral (black arrow) spaces B = bladder, R = rectum.

Fig. 7.-Schematic diagrams made via computer drawings show newer concepts regarding pathways and extensions of retroperitoneal spaces based on recent work, including our own. A, Revised axial diagram of three retroperitoneal spaces at level of kidneys. Newer concepts are the slender potential connecting conduit between the two perirenal spaces that border inferior vena cava (IVC) and aorta (A) anteriorly, and the anterolateral extension of posterior pararenal space that has close proximity to anterior pararenal spaces. AC = ascending colon, D = duodenum, P = pancreas, DC = descending colon, RK = right kidney, LK = left kidney, L3 = third lumbar vertebral body. B, Revised sagittal diagram of three retroperitoneal spaces through right kidney (K). Newer concepts are the pathways from anterior pararenal, postenor pararenal, and especially perirenal space to infrarenal and extraperitoneal spaces In pelvis. Note opening of perirenal space caudad to infrarenal space. D = duodenum, A = adrenal gland.

aneurysm, as seen in one of our cadavers. We do not prove that the great vessels (aorta, vena cava) are in the penirenal space, as these structures are not surrounded by contrast medium when the perirenal space is injected. On the other hand, the anterior margin of the great vessels comprises the posterior border of the channel connecting the two penirenal spaces. This is consistent with prior descriptions of blood from abdominal aortic aneurysm directly entering the perirenal spaces [12]. It is not surprising that penirenal fluid otherwise rarely is found to cross the midline in clinical practice. The midline channel is narrow and was crossed by contrast material only when large volumes were used by us and by Kneeland et al. [10]. Furthermore, these spaces are filled with fat and traversed by septa, preventing the free flow of fluid from one side to the other. In clinical practice, this could be a moot point, however, as we showed midline crossing may occur via the

infrarenal space when the midline penirenal channel is obstructed (the aneurysm case). Kneeland et al. [1 0] did not extend CT sections down to the bony pelvis and therefore did not evaluate the inferior margin of the cone of renal fascia. Raptopoulos et al. [11] included injections of contrast medium and color latex into perirenal spaces of cadavers with CT control and dissections and suggested that the caudal cone of renal fascia is closed. Our injections show that the cone is, in fact, open (Fig. 7B), at least in some subjects. Thus, even small amounts (35-SO ml) of contrast medium can readily escape from the cone down into the infrarenal space. When larger amounts (200900 ml) of contrast medium are injected, they may then exit the infrarenal space and reach the extraperitoneal spaces in the pelvis. The reason Raptopoulos et al. [11] did not identify an opening in the caudal cone of penirenal fascia is not clear.

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MINDELL

It may be related to the use of latex instead of water-soluble contrast medium, or perhaps their dissections altered pathways. Alternatively, it may be that not every person has such an opening in the cone; after all, the total number of cadavens studied by both Raptopoulos et al. [111 and our group is relatively small. We were unable to show direct flow from the peninenal space to the posterior or anterior pararenal spaces, but we know from our other injections and from prior published data that all these spaces do communicate with the infrarenal space. Our failure to fillthem may be related to technique, gravity, or other nonanatomic reasons. Beyond this, the injected contrast medium in all three spaces tended to flow “downhill” caudally, most likely because of gravity and the general orientation of the netropenitoneum.

Posterior

Pararenal

Space

We found no prior reports of CT-guided injections of contrast material into the posterior pararenal space. We showed that this posterior and lateral potential space is relatively slender, even in large subjects. An antenolateral track became apparent with large amounts of contrast medium (Fig. 4C). This could explain the observation of Heiken and Lang [1 3]that without a history of trauma, air-containing fluid collections in the posterior pararenal space are nearly always associated with colonic disease such as diverticulitis.

That

is, the anterolateral

track

of the posterior

pararenal space brings this space into proximity to the ascending or descending colon, where bacteria may break down fascial barriers between colonic segments located in the anterior pararenal space, permitting effusions to reach the adjacent posterior pararenal space. We confirmed that the posterior pararenal space connects to the infrarenal space, from which it may cross the midline or extend caudally into the pelvis (Fig. 4D). Contrast medium tracks toward the prevesical space (Fig. 4D), and we have unpublished data from a subsequent study of our own in which contrast material was injected directly into the extraperitoneal spaces of the pelvis of cadavers that clearly shows a pathway from the prevesical to the posterior pararenal space. All this is consistent with the hypothesis of Korobkin et al. [9] that the posterior pararenal space connects with the femoral sheath, the prevesical space, the anterior pararenal space, and the perirenal space via the infrarenal space.

Anterior

Pararenal

Space

We agree with Korobkin et al. [9] that the anterior pararenal space is “difficult to identify as a distinct compartment on CT except where it contains alimentary structures or where it is distended with fluid,” and we used the pancreas, always readily identified in our cadavers, as the marker for the injection of contrast material (Fig. 5A). A small amount of Contrast medium tracked retrograde around anteriorly placed needles (Fig. 5B), but we found no actual connection with the intraperitoneal spaces otherwise when contrast material was injected into the

ET

AL.

AJA:164,

May 1995

anterior pararenal space. We found nothing to support the thesis of Dodds et al. [1 4] that the anterior pararenal space is a component of the intraperitoneal space. Dodds et al. [14] were concerned in part that the posterior extension of the anterior pararenal space might be related to an intraperitoneal extension. In both of the anterior panarenal spaces injected, however, the distinct retrorenal extension (Figs. 5B and 6A) identified was concordant with the dissections by Raptopoulos et al. [5] showing two layers of the posterior renal fascia, explaining how the anterior panarenal space can have such an appearance. Further, our injections confirmed the communication of the anterior panarenal space with the infrarenal space and then with other extrapenitoneal spaces in the pelvis (Fig. 6B). We showed extension of the anterior pararenal space across the midline, although the factthatthis was mostly postenor to the pancreas could be related to needle position. With large amounts of contrast medium, the infrarenal space and the prevesical, perivesical, and presacral spaces fill (Fig. 6B). We did not show direct filling of the penirenal or posterior pararenal spaces from the anterior pararenal space.

ACKNOWLEDGMENTS We thank Bruce J. Fonda and Steven J. Arnold of the Departments of Anatomy and Neurobiology for their invaluable assistance in preparing the cadavers, and Susan Bushey for typing the manuscript. REFERENCES 1 . Love

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