localization of the placenta · the various methods of localization of the placenta have...

August' 952 RED:, The Radiological Locali;ation of the Placenta .445

when the counter moves from placenta to uterinemuscle only.

Summary and ConclusionsThe various methods of localization of the

placenta have been briefly reviewed.-A method using radio-active sodium has been

described.The results obtained in 255, cases have been

presented.It is concluded that this- method is- a useful

adjunct to the older radiological methods of diag-nosis of placenta praevia, and that it is of valuein enabling samples of maternal placental bloodto be obtained.

BIBLIOGRAPHYBURCH, C., REASER, P., and CRONVICH, J. (I947), J7. Lab

clin. Med., 32, xI6g.BURKE, F. J. (I935), J. Obst. Gynae. Bnt. Emp., 4a, I096.DIPPEL, A. L., and BROWN, W. H. (1940), Amer. Y. Obst. Gynec.

40, 986.ERHARDT, K. (1932), Kin. Wschr., III, 332, 20 Feb.LERICHE, R., BEACONSFIELD, P., and BOELY, C. (I952),

Surg. Obstet. Gynec., 94, I, 83.MARINELLI L. D., QUIMBY, E. H., and HINE, G. J. (1948),

Amer. J. Roentgenol., 59, 26o.Med. Res. Counc. (1949), Introductory manual on the control of

health hazards from radioactive materials, Issue 2. H.M.S.O.,London.

MENEES, T. O., MILLER, J. D., and HOLLY, L. E. (1930),Amer. Y. Obstet. Gynec., 24, 363.

MOIR, J. CHASSAR (I944), Amer. J. Obstet. Gynec., 47, I98.OLSSON, 0. (i94I), Acta Radiol., 22, 279.REID, F. (i49), Brit. J. Radiol., 22, 557.SNOW, W., and PWELL, C. B. (I934), Amer. J. Roentgenol., 31, 37.UDE,W.H., and.URNER, J. H. (I938), Amer. Y. Roentgenol., 40, 37.

THE RADIOLOGICAL LOCALIZATIONOF THE PLACENTABy FRANK REID, M.D.(Leeds), D.M.R.D.

Consultant Radiologist, Harrogate and Ripon Group o' Hospitals

During the latter half of pregnancy plain filmsof the abdomen show the foetus surrounded bya homogeneous soft tissue shadow which repre-sents uterine muscle, placenta and liquor amnii;the radiographic density of these tissues beingidentical, special methods have been developed todetermine the situation of the placenta.

Methods Employedi. AmniographyThe first attempt to localize the placenta radio-

graphically was made by Menees, Miller andHolly in 1930. They found that the injection ofstrontium iodide solution through the abdominalwall into the uterine cavity increased the radio-graphic density of the liquor and revealed theplacenta as a crescentic thickening of lesser densityon the uterine wall.

Reports of foetal death following the use ofstrontium led to a search for a less toxic contrastmedium; Uroselectan B was used in io patientsby Kerr and Mackey (1933) and by Burke (I935)in 75 patients; no ill effects were observed ineither. mother or baby, although in many .cases

labour commenced within a short time of in-jection.

Insertion of the needle through the abdominalwall is a further source of danger, damage- to theplacenta, cord or foetus having been reported insome cases.

2. Intravenous PlacentographyIn animal experiments Ehrhardt (I932) and

Katsuya (I932) *were able to differentiate theplacenta from the surrounding tissues followingthe intravenous injection of thorium dioxide, aradio-opaque substance which is taken up by theplacental reticulo-endothelial cells. Unfortunately,thorium is a radioactive substance and is generallyconsidered too dangerous to use as a contrastmedium.

In 1939, Ehrhardt was able to identify theplacenta in animals as an-opaque shadow followingthe intravenous injection of the phenyl and ethylesters of tri-iodo-stearic acid. Olsson (1941)employed the same contrast -medium in humanhepato-lienography (for which it was originallyintended), but considered it to be unsafe owingto the, dangerous reactions which occurred insome of his patients.

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446 POSTGRADUATE MEDICAL JOURNAL August 1952

3. ArteriographyAlthough translumbar aortography was first

described over zo years ago, it has only recentlybecome a generally accepted procedure. Accord-ing to Sante (I951) pools of radio-opaque mediumaccumulate in the sinusoids of the placenta andreveal its situation.

4. Soft Tissue RadiographyIn 1934, Snow and Powell described a soft

tissue shadow in a lateral view of the abdomenwhich they believed to represent the placentaand which had a maximum width of 7 cm.Amongst the many papers written in supportare those of Dippel and Brown (1940), Buxton,Hunt and Potter (I942), Stander (I942), MangesSmith (I943) and Bishop (I945). Dippel andBrown further stated that a placental shadowwhich is mostly or entirely below the level of themother's umbilicus is reliable evidence of placentapraevia.

5. TomographyLloyd and Samuel (I94I) used this procedure

in five cases and found evidence of placentapraevia in three; this diagnosis was subsequentlyconfirmed clinically in all three patients.

6. (a) CystographyThis method was originated by Ude, Weum

and Urner (1934), who injected contrast mediumthrough the urethra in order to reveal the softtissue space separating the fundus of the bladderfrom the foetal head; this, they considered,should not exceed i cm. in depth in normal cases.

6; (b) Air Inflation of the RectumDiagnostic errors in cases of posterior placenta,

apparently due to the use of cystography alone,led Sohne (I942) to devise a more embracingprocedure. Using air as a contrast medium, heinjected ioo c.c. into the bladder and I50 to 200c.c. into the rectum. Lateral films were takenand the space separating the foetal head from bothbladder and rectum was estimated; the normalrange in either instance was found to lie betweeno.8 and 2.I cm.

7. Displacement MethodStating that the foetal head should normally lie

in the mid-coronal and mid-sagittal planes of theinlet when the patient is standing upright, Goldenand Ball (i941) went on to say that displacementof the head from either plane by a third or moreof its diameter was an indication of placentapraevia. They considered that their method wasapplicable in vertex presentations only and that

other causes of displacement such as loaded rec-tum, distended bladder or pelvic tumour had tobe excluded.

Brailsford (I947) published postero-anteriorand lateral radiographs, taken with the patientstanding, which showed a wide separation of thefoetal head from the promontory; the films hadbeen sent to him by Dr. F. H. Kemp to show howradiography in the erect position without the useof contrast media might reveal obstruction of thepelvic brim due to placenta praevia, provided thequestion of distended bladder or other space-occupying mass could be excluded.

In neither of these publications was there anymention of the subsequent history of patientswith radiographic evidence of placenta praevia.

The Radiographic Appearances of theNormally Situated PlacentaThe placenta is of the same radiographic density

and cannot therefore be differentiated from the sur-rounding uterine muscle and liquor amnii; never-theless, in most cases a crescentic expansion of

strterior

FIG. I .-Radiographic interpretation. Normal posteriorplacental shadow.

the anterior or posterior wall of the uterus canbe demonstrated, which has proved in practiceto be reliable e of its 'situatio. Implanta-tion being nearly always anterior or posterior,a lateral radiograph of the abdomen is requiredto show this so-called'placental shadow.

Interpretation of the lateral radiograph isexplained diagrammatically in Fig.I.o An in-terrupted line encloses the foetus and delineatesa peripheral soft tissue shadow of fairly uniformwidth anteriorly but which expands into theshape of a crescent on the posterior wall. Theelatter is a composite shadow which comprisesuterine muscle, placenta and liquor amnii; itis usually some 4 to7 cm. in depth at the centreand aboute20 to 25 cm. ong; at either end it

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August 1952 REID: The Radiological Localization of the Placenta 447

merges- into a fairly uniform band between i and--cm. wide, which represents muscle and liquor

only. Correcting for radiographic magnification,these figures become 3 to 52 cm., I5 to 20 cm.and o.8 to I.2 cm., respectively, the average ofeach range being 41 cm., I7- cm. and i cm. Butthe depth of the placental shadow is partly dueto uterine muscle and liquor, the combined con-tribution of which should be approximately equalto the depth of shadow on the opposite wall;hence the average cross-section of placenta pro-jected in lateral radiographs is approximately I721cm. long and 31 cm. (4j-I cm.) in depth at thecentre, dimensions which are not far removedfrom those quoted by standard textbooks.

Variations in the shadow due to the size of theplacenta would be expected, but this is not theonly factor concerned: its maximum thicknesswill not always be projected by the X-ray beam,other variables being the width of the uterinemuscle and the amount of liquor around the foetus.Fig. 2 shows how asymmetrical implantation, orobliquity of the uterus, may cause projection ofthe tapering periphery of the placenta and, inextreme cases, how most of the placenta may beon the posterior or anterior wall without any partbeing in profile to the lateral X-ray beam.

Radiography in Erect Position(a) Anterior and Posterior ImplantationThe dimensions of the uterine soft tissue

shadows given above were obtained from filmstaken with the patient lying on her side. Butwhen radiography is performed in the erectposture the anterior placental shadow rarelyexceeds 4 or 5 cm. in depth, the reduced figurebeing almost certainly due to the altered distribu-tion of the liquor which occurs as the foetus sinkson to the inclined anterior uterine wall (Fig. 3).On the other hand, the average depth of the

posterior placental shadow in the erect position isappreciably greater than the average measurementfound in radiographs taken with the patient lyingdown. The explanation for this is probably asfollows: when the mother lies on her side thefoetus gravitates towards the lower lateral uterinewall, the depth of fluid anteriorly and posteriorlytending to be approximately equal, but when sherises to her feet, the foetus moves and sinks onto the anterior uterine wall, displacing liquorwhich becomes available to increase the depth offluid posteriorly.

Occasionally a lateral radiograph shows anequally acceptable placental shadow on bothanterior- and posterior walls. Nevertheless, pro-vided the film was taken in the erect position, it issafe to assume-with rare exceptions-that im-

TAUE LEVEL E/FILM LEVEL

PLACENTALSHADOW

FIG. 2a

.

TABLE LEVELFIM LEVEL L

PLACENTALSHADOW

FIG. 2b

TAKEELEVEL/FILM LEVEL

Fic. 2cFIG. 2.-Projection of placental shadow in lateral

recumbent position. (a) Symmetrical implantationon anterior or posterior wall. (b) Symmetricalimplantation. Maximum depth of placenta nolonger in profile to the X-ray beam owing to lateralobliquity of uterus. (c) Implantation asymmetricaland extending on to lateral wall. No ' placentalshadow ' projected.

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FIG. 3a.-Normal Anterior placental shadow (patientlying on her side).

plantation is anterior, and that a somewhatexcessive amount of liquor lies posteriorly.A crescentic thickening of the uterine wall

which extends to the fundus does not necessarilyexclude the possibility of implantation being alsoon the lower segment. The situation of theplacenta can only be considered to be normalwhen films taken in erect or semi-erect positionsshow the presenting part within I-1 cm. of bothpubis and sacral promontory, and also inthe central pelvic axis in the antero-posteriorprojection.(b) Lateral Implantation

In my experience it is uncommon for theplacenta to be completely on one or other lateraluterine wall. Nevertheless, on rare occasions I havesuggested such a diagnosis when no placentalshadow was visible on either the anterior orposterior uterine walls and low implantation couldbe excluded. In one of these cases, delivered byCaesarian section owing to disproportion, theplacental site was, in fact, confined almost com-pletely to one lateral wall of the upper segment.

It is also possible, on theoretical grounds, thatthe radiographic appearances may differ from theabove description and resemble those of a normalposterior placenta. The only requirement would

FIG. 3b.-Normal anterior placental shadow (erectposition).

be a sufficient amount of liquor amnii to form apseudo-placental shadow on the posterior uterinewall. I am not aware of any mistakes in diagnosisarising in this way, but they would, in any case,be of only trivial importance.

The Radiological Diagnosis of PlacentaPraeviaThe procedure which I adopted when working

at the Radcliffe Infirmary, Oxford, is straight-forward, does not require the use of contrast mediaand can be performed in any department whichpossesses X-ray apparatus capable of producinga lateral radiograph of the pelvis in advancedpregnancy. Interpretation of the films dependson the following basic principles:

i. The actual, or potential, site of junction ofthe upper and lower uterine segments during theinlet. A placenta praevia, therefore, is likely tocause a substantial thickening of the uterine wallat the level of the brim.

2. With the foetus lying longitudinally andthe mother in an upright position, the presentingpart sinks downwards through the liquor untilarrested in the lowest part of the uterine cavity.In normal cases, radiographs taken with thepatient standing or, if necessary, reclining back-wards (semi-erect) should show the presenting

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August 1952 REID: The Radiological Localization of the Placenta

part in the central pelvic axis in the A-P view; inthe lateral film it should be within a distance of thepubis and the sacral promontory, which does notgreatly exceed the thickness of the interveninguterine muscle.

3. The increased depth of the uterine wall atthe pelvic brim due to placenta praevia displacesthe presenting part from its normal positiGn; itmay be shifted laterally to one gr other side of thepelvis, backwards and upwards from the pubis,forwards from the promontory, or in more thanone direction.

Radiographic TechniqueIn cases referred to the X-ray department with

a specific request for placental localization, filmsare taken as follows:

i. Lateral View of Abdomen (Erect Position).A differential filter (Reid, 1949) may be used tocompensate for the widely different density of theanterior and posterior tissues, but its use is notessential. Alternatively, two exposures can bemade with different degrees of penetration, or asingle well-penetrated radiograph may serve ifexamined with variable illumination.

2. Lateral View of Pelvis (Erect Position). Thepatient should micturate immediately beforeX-ray examination or serious fallacies in diag-nosis may arise. A measuring device is usuallyemployed for determination of diameters anddistances in the sagittal plane.

3. Antero-Posterior View (Semi-Erect Position).If a tilting table is available the patient lies onher back and the head is raised about 600. Ex-posure is made with the X-ray tube perpendicularto the table. A similar view can be obtained ona horizontal couch by raising the patient from thesupine position and supporting the shoulders atan angle of approximately 40 to 600.The object of this projection is to show any

lateral displacement of the presenting part whichmight be due to a placenta praevia lying to oneor other side of the pelvis. The semi-erectposition was chosen in preference to the uprightas it seemed more favourable for the presentingpart to gravitate downwards along the centralpelvic axis and less dependent on the state of themothers' abdomninal muscles.The patient remains on the table until the first

three radiographs have been processed. The filmsare inspected and, if the lateral views show apresenting part-promontory gap which measures2 cm. or more, a fourth radiograph is required.

4. Lateral View of Pelvis (Semi-Erect Position).In this position the presenting part should gravi-tate downwards and finally come to rest on theposterior uterine wall in the region of the sacralpromontory. A gap which measures more than

2 cm. across is unlikely to be occupied by uterinemuscle only and indicates a displacement of thepresenting part due to placenta or to pelvic tumour.

Rddiological InterpretationThe following factors have to be considered in

the X-ray diagnosis of placenta praevia:i. The nature of the presenting part.2. The stage of pregnancy at the time of

examination.3. The situation of the placental shadow.i. The Presenting Part. The radiographic tech-

nique was designed to provide the most favourableconditions for gravitation of the foetus towardsthe pelvis in order to estimate the thickness ofthe uterine wall at the level of the brim. Thebest results are obtained in cephalic presentations;the shape of the foetal head ensures the greatestpossible contact with the walls of the lower seg-ment and, in addition, the calcified outline of thecranium is clearly visible radiographically.When the breech is presenting there are two

disadvantages compared with head presentations:in the first place, accommodation in the loweruterine pole is less accurate and, secondly, theoutline of the foetal parts, a translucent bandrepresenting subcutaneous fat, is difficult todemonstrate in the region of the pelvis.A transverse lie is the most frequent cause of

difficulty in interpretation. In some cases a wideseparation of the nearest foetal parts from thepubis or promontory, or from both, may bewholly due to placenta praevia; it is also feasiblethat the foetus is unable to sink into the lowerpole of the uterus owing to its unfavourablesituation, and that the wide soft tissue shadowslying below are mostly due to liquor amnii; athird possibility is that the gap between thepresenting part and the pelvic brim contains bothliquor and placenta, the transverse lie being dueto the limited capacity of the lower uterine cavityresulting from low implantation.

2. The Stage of Pregnancy. X-ray examinationfor placenta praevia can provide useful informationat any time between the 28th and 40th weeks, butthe significance of the radiological findings varieswith the stage of pregnancy. The following is atypical example of the changes which are oftenfound on serial radiography during the lasttrimester.

Mrs. W. W. was referred to the X-ray depart-ment at 31 weeks because of a small A.P.H. Theradiographs showed a vertex presentation, the headbeing i.O cm. above the pubis; in the semi-erectposition it was 4.1 cm. from the promontory anddisplaced slightly to the right. As the placentalshadow was posterior, these findings indicatedextension downwards over the promontory on to

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the posterior and left lateral walls of the lowersegment. The radiological diagnosis was lowposterior implantation and probably placentapraevia. At 36 weeks the presentation had notaltered; the head-pubis distance was I.3 cm., thehead promonotory gap was now 3.6 cm. and therewas no longer any doubt about the diagnosis ofplacenta praevia. Further confirmation was ob-tained at 372 weeks when the head was i cm. fromthe pubis and 3.2 cm. from the sacral promontory.A few days later, Mr. Stallworthy performedCaesarean section and found the placenta situatedposteriorly, extending downwards to the edge ofthe internal os and also slightly on to the leftlateral wall of the lower segment.

In the above and similar cases the diminishingdisplacement of the presenting part can beexplained by expansion of the lower segment andcontinuing growth of the uterus; in consequencethere is a decreasing depth of placenta at the brimdue to the upward movement of its pelvicextension.

In other patients, the presenting part is found tobe displaced on first examination, but normallysituated in radiographs taken a few weeks later.Although the later findings show the placentaentirely in the abdomen, its lower margin mayhave been below the pelvic brim when the firstX-rays were taken. In these cases it is impossibleto say whether implantation is normal but un-usually low, or extending slightly on to the lowersegment; further differentiation would requireprecise knowledge of the site of junction of theuterine segments.

The X-Ray Diagnosis of Placenta PraeviaThe factors involved are so variable that no

hard and fast rules can be laid down. Neverthe-less, information can be obtained in most caseswhich is reliable, sufficiently accurate to be usefulto the obstetrician and without risk to eithermother or baby. During the last five years I havemade a detailed analysis of the X-ray findings inwell over 700 patients (Reid, 1949 and I951) inthe light of their subsequent clinical histories.The method of radiographic interpretation whichis outlined below is based on the experienceacquired in these cases. It should not be appliedtoo rigidly but used rather as a guide, eachparticular case being considered on its own merits.

Lateral radiographs show the presenting partwithin I cm. of both pubis and promontory.

(a) Transverse Lie. Placenta praevia can beexcluded.

(b) Breech or Head Presentations. Placentapraevia can be excluded, provided the A.P. view

shows the presenting part lying in the centralpelvic axis.

The placental shadow is continuous with a softtissue space separating the presenting part fromeither the pubis or the promontory which measures

249 to 2 cm.(a) Transverse Lie. Placenta praevia can be

excluded.(b) Breech or Head Presentations.Twenty-eight to thirty-four weeks.-Placenta

praevia can be excluded if there is no lateraldisplacement of the presenting part.

Thirty-four to forty weeks.-Unless the patienthas been X-rayed at an earlier stage of pregnancyre-examination is advisable within one to twoweeks. Placenta praevia can then be excludedif the soft tissue gap is less than i cm. and thereis no lateral shift of the presenting part. Noappreciable change in the width of the soft tissuespace is suspicious of placenta extending down-wards to the brim, but any significant degree of'implantation on the lower segment is unlikelyunless there is also some lateral displacement.If similar, or wider, displacement was present atan earlier stage of pregnancy, the findings indicatea minor degree of placenta praevia.

The placental shadow is continuous with a softtissue space separating the presenting part fromeither the pubis or the promontory and the depth ofwhich measures more than; cm.

(a) Transverse Lie.Twenty-eight to thirty-four weeks.-A soft

tissue gap measuring 2 to 3 cm. is unlikely to beof any significance. A distance of 3 to 4 cm. isprobably due to low normal implantation or aminor degree of placenta praevia. If the spacemeasures more than 4 cm. the possibility of a majordegree of placenta praevia has to be considered.

Unless a radiological opinion is urgentlyrequired it is usually advisable to temporize and,if the obstetrician is willing to co-operate, awaitfurther X-rays after version. The head or breechis often found to be presenting when the patientarrives for re-examination; if not' version at-tempted may be preferably in or near the radiologydepartment so that films can be exposed withthe least possible delay in case the malpresentationshould recur.

Thirty-four to forty weeks.-Placenta praeviacan be excluded if the displacement is less than

2- cm. and a major degree of the condition neednot be considered unless the distance exceeds 3cm.

(b) Breech or Head Presentations.Twenty-eight to thirty-four weeks.-A tentative

diagnosis of ' low lying' placenta can be made.The likelihood of placenta praevia increases with

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August 1952 REID: The Radiological Localization of the Placenta 45X

BEFORE MICTURITION LATERAL PELVIS. AFTER MICTURITIONLATERAL PELVIS ERECT POSITION ERECT POSITION

04 04cm.

FIG. 4.-Upward displacement of foetal head due to full bladder.

the degree of displacement; in addition a givendisplacement from pubis or promontory is moreconvincing evidence when the presenting part isalso displaced laterally.

If the pregnancy continues, further X-raysshould be obtained after an interval of two, threeor four weeks and, where time allows, a third.examination is often useful. When the radio-graphic appearances are normal at the second, orlater, investigation, placenta praevia can beexcluded; persistent displacement of the present-ing part shows some degree of implantation onthe lower segment.

Thirty-four to forty weeks.-Placenta praeviais indicated when a similar or greater displace-ment was present at an earlier stage of pregnancy.In cases not examined previously further X-raysmay be useful after a relatively short interval ofone to two weeks; if these show little or no changea more confident diagnosis of placenta praeviacan be made.The amount of displacement of the presenting

part is not always in proportion to the type ofplacenta praevia, but radiologically it is usuallypossible to differentiate between a minor or amajor degree. For example, if the head or breechis 4 cm. or more from the pubis or promontoryand, in addition, some 2 cm. or more to one sideof the central pelvic axis, then the placenta isalmost certainly extending well down into thepelvic cavity, with its lower margin in the neigh-bourhood of, or completely covering, the internalos. On the other hand, when- the anterior orposterior displacement of the presenting part doesnot greatly exceed 2 cm. and there is no associatedlateral shift, there is unlikely to be more, than aminor degree of extension on to the lower segment.

Differential DiagnosisFull Bladder (Fig. 4)

It is a wise precaution to make a routine requestof all patients to empty the bladder immediatelybefore X-ray examination. On several occasionsI have found appearances of anterior placentapraevia in patients who had not recently passedurine; further lateral films, taken immediatelyafter micturition, showed a normal distance fromthe pubis to the presenting part and therebyexcluded any question of placenta praevia. Innone of these cases did the bladder seem to bedistended and the two or three ounces of urineusually voided was enough to restore the radio-graphic appearances to normal.

Loaded BowelAn accumulation of faeces in the pelvis is easy

to recognize in a good lateral radiograph andis a fairly common finding in late pregnancy.Although well known clinically as a cause of non-engagement, it is only rarely that a loaded bowelis found to be responsible for displacing thepresenting part from the pelvic brim. Neverthe-less, the possibility must be considered when theradiographs show displacement from the sacralpromontory, a posterior placental shadow and amass of faeces in the pelvic colon or the rectum.In these circumstances, diagnosis should be post-poned and the patient re-examined after defaeca-tion or, if necessary, following an enema; per-sistence of the presenting part displacement showsthe presence of a posterior placenta praevia andindicates that the loaded bowel in the earlierfilms was merely an incidental finding.

In other cases the placental shadow is anteriorand the presenting part displaced from the pro-

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montory but in normal relationship to the remain-der of the pelvic brim. Although here a loadedrectum is the most likely cause of displacementand placenta praevia can be excluded, it is,nevertheless, advisable to re-examine the patientafter defaecation. Little or no change in, thepresenting part-promontory distance indicates atumour in the posterior part of the pelvis.

Pelvic TumoursRadiographs of the pelvis in pregnancy oc-

casionally reveal app'earances typical of a boneneoplasm, a calcified fibroid or a dermoid cyst.But the radiographic density of most tumoursis identical with that of uterine muscle, placentaor other neighbouring soft tissues and radiologicaldiagnosis is only possible when the mass is largeenough to displace the presenting part from itsnormal relationship to the pelvic inlet. Differ-'entiation from placenta praevia may be difficult,but is sometimes possible when there is no radio-graphic evidence of continuity between theplacental shadow and the soft tissue space at thesite of the presenting part displacement.

CI1: Outline oftumour visible.

9.2cms 1.6cn's.

FIG. Sa.-J.C. Posterior pelvic tumour. Lateral viewof pelvis (semi-erect position).

In Fig. 5, for example, the foetal head was dis-placed 4.7 cm. forwards from the promontory;the placental shadow was anterior, but the normalrelationship of-the head to the pubis and lateralmargins of the brim excluded any possibility ofextension downwards into the pelvis. No furtherevidence was required for the diagnosis of atumour, but in this particular case the roundedoutline of a soft tissue mass wag visible in frontof the sacrum by virtue of the gas containedl inthe pelvic colon and rectum. My diagnosis of atumour in the posterior part of the pelvis was

verified at Caesarean section when a fibroid thesize of an orange was found on the posterioruterine wall below the sacral promontory.

Radiographic appearances resembling those inthe case described above are conclusive with orwithout the demonstration of the tumour itself,but differential diagnosis from placenta praeviais impossible when the placental shadow is con-tinuous with the soft tissue gap which separatesthe presenting part from the brim. Even if theoutline of a tumour is visible in the pelvis, thepossibility of displacement being due, partly orwholly, to placenta praevia cannot be excluded.

wall

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FIG. sb.-J.C. Lateral abdomen (erect). Anteriorplacental shadow not extending into pelvis.

4 *1*. c..)

FIG. Sc.-J.C. Antero-posterior view of pelvis (semi-erect). Foetal head in normal situation.

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August I952 REID: The Radiological Localization of the Placenta 453

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Lax AbdominalMuscles

In the upright position the foetus gravitatesdownwards and, in normal cases, backwards inthe direction of the pelvic inlet. But when thetone of the abdominal muscles is impaired, thereis a tendency for the presenting part to dropdirectly down aad become arrested either im-mediately above tle pubis or, in extreme cases,further forwards where a pouch is formed by thesagging abdominal wall. Nevertheless, a laxabdomen should not be accepted too readily asthe cause of a presenting part which lies too farforward; it is important to remember that theabnormal situation of the foetus may be due toplacenta praevia or a pelvic tumour, and that theimpaired abdominal musculature may be merelyincidental. To differentiate, further films shouldbe taken in the semi-erect position; providedthese show the presenting part within one or twocentimetres of the promontory and also equi-distant from the lateral margins of the inlet,placenta praevia and tumour can be excluded.

The Early Diagnosis of Placenta PraeviaThe displacement method causes the patient

less disturbance, and has proved more successfulthan procedures which involve the use of contrastmedia. A further advantage is derived from thesimple nature of the radiographic technique em-ployed. By including the erect lateral radiograph-diagnostic in over 95 per cent. of cases-as anintegral part of all X-ray examinations in preg-nancy, placenta praevia is sometimes revealedbefore the onset of haemorrhage.A recent series of 32 clinically confirmed cases

of placenta praevia included I7 patients who hadbeen examined radiologically because of a previousA.P.H. Although the remaining 15 gave nohistory of A.P.H., some were referred for X-rayexamination because placenta praevia was sus-pected clinically, the others being sent for routineinvestigation of non-engagement, transverse lie,etc. The i patients examined and diagnosedradiologically before the onset of haemorrhageincluded four cases of central placenta praevia andseven of Type I.

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Summary of ResultsThese examinations were carried out during

a period of two years and nine months fromOctober i, I947, to June 30, 1950.

RADIOLOGICAL APPEARANCES OF NORMAL PLACENTA IN754 PATIENTS

No. ofcases

Site of ImplantationAnterior wall .. .. .. 347Posterior wall 391Precise situation not identified, but placenta

praevia could be excluded I6

Total . 754

Clinical evidence of placental site(a) Normal implantation:

Situation noted at C.S. .. 62,, , manual removal 6

Total .. 68

Radiological localisation confirmed .. 67incorrect .. I

Total .. 68

(b) Placenta praevia:Incidental finding at C.S. for dispropor-

tion, etc. Placenta extended for shortdistance on to L.S.; lower margin wellabove the I.O. in all cases 3

RADIOLOGICAL APPEARANCES OF PLACENTA PRAEVIA INI I 7 PATIENTS

No. ofcases

Site of implantationAnterior (or predominantly anterior) . 53Posterior ( ,, ,, ,, ) . 64

Total .. II7

Clinical evidence of placental site(The 117 cases consists of two series investigated duringsuccessive periods of 15 and i8 months (Reid, 1949 and195i). Comparison of the results obtained is instiuctive)

I st series 2nd seriesExamined Examinedbetween between1.10.47- 1.1.49-3112.48 30.6.50

(I5 mths.) (I8 mths.)

No. of cases No. of casesX-ray appearances of placenta

praevia .. .. .. 73 44Complete clinical proof ob-

tained at C.S. or palpationp.v. .. .. 22 32

Unreliable evidence of pla-centa praevia from inspec-tion after delivery, etc. . . 9 6

No clinical evidence of pla-centa praevia at delivery . . 42 6

Proportion of proved/un-proved cases .. .. 30% 73%

The great improvement in results during thelater period was solely due to a mnYch higherproportion of follow-up examinations. The firstseries included a large number of cases who wereX-rayed on one occasion only, in the earlier partof the last trimester. Radiographic evidence oflow implantation was found, but on subsequentclinical examination the head had engaged andthe obstetrician being no longer concerned aboutthe possibility of placenta praevia no further filmswere taken.As the work developed and clinical co-operation

increased, more and more cases were referred tothe X-ray department for re-examination. Duringthe second period, therefore, placenta praevia wassuspected radiologically in many patients, butwas subsequently excluded by the same means.Although low implantation was usually alsoexcluded at about the same stage by clinicalexamination, the striking reduction in the numberof unverified cases was a more convincing in-dication as to the value of the method.

AcknowledgementWe would like to acknowledge with thanks the

permission to reproduce figures I, 2a, b, c and 4from the 'British Journial of Radiology' andfigure 7 from the 'Proceedings from the RoyalSociety of Medicine.

BIBLIOGRAPHYBISHOP, P. A. I945), Surg. Clin. N. Amer., 25, 1394.BRAILSFORD. J. (I947), Medical Annual.BURKE, F. J. (1935), 7. Obst. Gynec., 42, I096.BUXTON, B. H., HUNT, R. R., and POTTER, C. (I942), Amer.

Y. Roentg., 43, 6io.

DIPPEL, A. L., and BROWN, W. H. (1940), Amer. _'. Obst. Gyn.,50, 986.

DIPPEL, A. L., and BROWN, W. H. (1946), Bull. Johns Hopk.Hosp., 46, go.

EHRHARDT, K. (1932), Klin. Wschr., II, 332.

EHRHARDT, K. (I939), Zbl. Gynak., 43, 2335.

GOLDEN, R., and BALL, B. P. (I94I), Amer. Y. Obst. Gyn., 62,530.

KATSUYA, S. (1932), Yap. Y. Obst. Gyn., I5, 77.

KERR, J. M. M., and McKAY, W. G. (1933), Trans. Edin. Obst.SOC., 21.

LLOYD, O., and SAMUEL, E. (1941), Y. Obst. Gyn., 48, 499.MENEES, T. O., MILLER, J. D., and HOLLY, L. E. (1930),

Amer. Y. Roentg., 24, 363.OLSSON, 0. (194I), Acta Radiol., 129.

REID, F. (I949), Brit. Y. Radiol., 22, 254; 22, 262.

REID, F. (I95 ), Proc. Roy. Soc. Med., 44, 703.

SANTE, L. R. (195I), Radiology, 56, I83.SMITH, R. MANGES (I943), Amer. 5. Roentg., 37, 49.

SNOW, W., and POWELL, C. B. (1934), Ibid., 31, 37.

STANDER, H. J. (I942), Amer. 5. Obt. Gyn., 44, 53I.SOHRNE, G. (1942), Acta Radiol. Stockh., 23, 6, 54I.UDE, W. H., WEUM, T. W., and URNER, J. A. (1934), Amer-

5'. Rsentg., 31, 230.

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