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Thorax (1970), 25, 490.
Congenital cleft sternum
A. EIJGELAAR and J. H. BIJTEL
Department of Thoracic Surgery of the Surgical Clinic, and Department of Embryology of the Anatomical Laboratory, State University, Groningen, The Netherlands
The embryonic development of the sternum is discussed in an effort to explain the pathogenesis
of cleft sternum (fissura sterni congenita). The treatment of one patient with such an anomaly is
described. The operative indication, operative technique, and timing of the correction are discussed
in some detail.
Total or partial fissure in the middle of the
sternum (cleft sternum or fissura sterni congenita)
is a^ rare congenital anomaly.
Absence of skeleton in the front part of the
chest wall (^) gives rise to a (^) severely paradoxical movement of this part of the thorax (Figs 1 and
2). Moreover, the pulsations of the heart and large
vessels are clearly visible because they are covered
only by soft tissues. The anomaly is caused by a disturbance in
embryonic development, of unknown origin. This
disturbance in embryonic development may lead
to various degrees of^ cleft^ sternum^ (de Groot^ and
Huizinga, 1954):
1. The presence of non-fused, ossified episternalia;
2. Total or partial cleft sternum. In total sternal FIG. 2. Retraction of soft parts in^ inspiration.
fissure the^ two^ halves^ of the^ sternum^ are^ entirely separated. In^ the^ more^ severe^ cases^ of^ partial fissure takes the shape of a triangle with the apex fissure, only the xiphoid process is^ fused, and this^ in a caudal direction;
3. A very rare situation is non-fusion^ of the caudal
portion of the sternum, which produces a triangu-
lar defect with the apex in a cranial direction.
Congenital perforations of the sternal body also
come under this heading;
- A cleft xiphoid process is^ a^ common^ anomaly;
in fact it is likewise a^ modality of non-fusion of
the caudal portion of the sternum.
EMBRYOLOGICAL INTRODUCTION
For an understanding of the pathogenesis of these
sternal anomalies the development of the human embryo has^ first^ to^ be^ considered. Until the (^) beginning of the third week, the embryonic primordium lies^ practically^ flat^ on^ the
FIG. 1. Protruding soft parts in expiration. yolk^ sac.^ In the^ course^ of this week the three germ
..-. - -. - (^) -.--.-C, --, -^ ---- --
Congenital cleft sternum
layers become visible-the ectoderm and the ento-
derm with the notochord and the mesoder,m in
between (Fig. 3). At the same time the head part
of the embryo begins to rise above the surface
and to detach itself, soon followed by the tail part,
so that a cranial and a caudal fold are formed.
FIG. 3. Transverse section through an embryo in the
third week. Development of the three germ layers.
Simultaneously, the future dorsal part of the
embryo begins to bulge upwards into the amniotic
cavity. These processes continue during the f,ourth
week (Fig. 4). Towards the end of the third week the paraxial
mesoderm begins to show metametic segmenta-
tion. On either side of the notochord somites are
formed. They are linked by the inter-mediary
mesoderm with the more laterally located unseg-
mented lateral plate mesoderm. Small cavities
originate in the latter and unite to form the secon-
dary body cavity or intra-embryonic coelom.
A short time later the latter joins with the extra-
embryonic coelom. The formation of the coelom
causes the lateral plate mesoderm to divide into
two layers-a parietal or somatic and a visceral
or splanchnic layer, which at this stage arrange
themselves against the ectoderm and the entoderm
respectively (Fig. 5).
The part of the body wall lateral to the somites
(the somatopleure) has meanwhile started to fold,
HEAD FOLO
FIG. 4. Schematic representation of a median section through an embryo at the beginning of the fourth week.
X1'-^ HEAO FOLD NEURAL TUBE
0 0-SOMI ITEECTOORECTM
-r-- -- (^) TAIL FOLD ATE i-</ COELOM SPLANCHNIC MESOOERM LATERAL PLATE MES SOERMSOMATIC MESODERM
A B
FIG. 5. A. Embryo at the beginning of the fourth week. B. Transverse section
through the same embryo.
Congenital cleft sternum
for such parts as the dermis^ and^ hypodermis
(dermatome) and muscular tissue for segmented
muscles (myotome) (Fig. 7).
It is not until the sixth week of human embry-
onic development that the 'anlage' of the sternum
becomes visible. It appears in the form of two
mesenchymal bands which arise on either side in
the ventral body wall far from the mid-line. That
the 'anlage' is paired is linked up with the fact
that the young embryo initially lies flat on the
yolk sac. In all animal species, whose embryos
develop in^ this^ way,^ the^ sternum^ originates^ from
two separate mesenchymal bands. These^ sternal
bands are formed independently of the ribs, which
arise from the sclerotomes. At this^ early^ stage^ the
bands show no connection with the distal ends^ of
the primordia of any of the separate ribs. In this
context we refer to Whitehead and Waddell (1911),
Hommes (1921), and Gladstone and Wakeley
(1932), who examined mammalian embryos for
this purpose. Whitehead and Waddell and Glad-
stone and^ Wakeley examined^ young^ human
embryos as well.^ In^ human^ embryos^ the^ two mesenchymal sternal bands are present in the
sixth week of development (Brandt, 1949;^ Patten,
1968). In a human embryo of 105 mm.,^ examined
by Whitehead and^ Waddell, no^ costal^ primordium
directly reached as far as any^ of^ the sternal^ bands.
These facts were convincingly confirmed by^ Fell
(1939), who experimented on^ chick^ embryos,^ and
by Chen (1952a, b, 1953), who made similar ex-
periments on mouse embryos. Both investigators
were able to demonstrate that the sternum evolves
from two mesenchymal condensations, which not
only develop without intermediation of the ribs
but are capable, in vitro, of moving towards the
median plane and fusing there without costal inter-
vention.
These findings justify rejection of the view that
the sternal bands develop as a result of the union
of the successive costal blastemas. The reconstruc-
tions by which Muller (1906) documented this
view are undoubtedly of importance. The stages
of development of the embryos, however, from
which she made these reconstructions were too
advanced to allow conclusions concerning the first
'anlage' of the human sternum.
In the^ development of^ the^ sternum,^ the
'anlage' of the^ manubrium requires^ further con-
sideration.
Apart from the sternal bands a few blastemas of different nature participate in this anlage. In the human embryo, too, these structures are
visible in certain developmental stages as^ mesen-
chymal blastemas. Between the ventral ends of
the primordia of the left and the right clavicle,
a pair of blastemas has been observed by Eggeling
(1906), Reiter (1942), and Klima (1968). They
described them as 'suprasternal structures'. These
two structures are localized in line with the
cranial ends of the two sternal bands, with which
they fuse afterwards.^ In^ addition,^ an^ unpaired
mesenchymal condensation is localized between
the caudal ends of the^ suprasternal structures;
this was described by^ Eggeling,^ Reiter,^ and
Klima as a^ 'precostal^ process'.^ Klima^ depicted
thes,e three structures in sections through embryos
of 21 and 27 mm. They are visible during a^ short
time only.
The development of the manubrium thus
involves the blastemas described as suprasternal
structures and the precostal process, as well as
the cranial parts of the^ sternal bands^ situated^ at
the level^ of the^ first rib^ (Fig.^ 8).
With regard to^ the^ development of^ the
manubrium sterni it^ may be^ pointed out^ that^ the
suprasternal structures are^ sometimes^ homo-
logized with special elements of^ the^ coracoid,^ i.e.,
with components of the shoulder girdle. In^ any
case their origin lies in a^ region which^ differs
from the region of origin of the^ sternal bands.
"SUPRASTERNAL SrRUcTuRE" "PRECOSTAL PROCESS'
X,.
.....
A
..
FIG. 8. Development of the sternum: A. After Klima (1968); B. After Reiter^ (1942).
A. Eijgelaar and J.^ H.^ Bijtel
The origin of the precostal process is^ even^ more difficult to^ explain. Both sternal^ primordia,^ each^ consisting^ of^ a sternal band^ with^ a^ suprasternal^ structure^ at^ its cranial end, have^ their^ first^ contact^ at^ the cranial end of the thorax. Klima^ demonstrates^ the^ start of the fusion in a reconstruction^ of^ the^ sternum of an embryo of 17 mm.^ This implies^ that^ the fusion starts in about the seventh^ week.^ At^ this stage each of the sternal bands^ has^ begun^ to
fuse with its adjoining suprasternal structure.^ As
the fusion of the left and the right sternal primor- dium proceeds in a caudal direction the more^ ven- trally localized unpaired^ precostal^ process^ is enclosed by them. Klima^ depicts^ this^ enclosure in sections of embryos of^21 and^27 mm.^ The fusion of^ the^ more^ caudal^ parts^ of^ the^ sternal
bands is completed during the^ ninth^ or^ tenth^ week
(Muller, 1906; Patten, 1968). The question which now^ arises^ concerns^ the
source of the material for the 6ternal body.^ In
view of what has been said about the manubrium
it is plausible, not^ only^ on^ embryological^ but^ also
on phylogenetic grounds,^ that^ the^ material^ of which the sternum is^ made^ up^ originates^ from two different sources. In the older view^ the^ sternal^ bands,^ as^ a^ pro- duct of union of the ribs^ (Muller,^ 1906),^ are^ sup- posed to derive their material from the^ somites by way of the sclerotomes. However, since it^ has been established that the sternal bands^ develop
independently of the ribs, it is questionable
whether their^ material^ derives^ from^ the^ somites. This question has been^ explicitly expressed^ by
such authors as^ Seno^ (1961), Murillo-Ferrol^ (1963),
and Pinot (1969). As a result of experiments which^ were^ per- formed in different ways on^ chick^ embryos,^ these authors came to the^ conclusion^ that^ it^ is^ the lateral plate that^ gives^ rise^ to^ the^ sternum. According to Seno, not only the^ sternum^ arises from the lateral plate but the^ skeleton^ of^ the
wing and the pectoral muscle^ as^ well.^ Neither
Seno, Murillo-Ferrol nor^ Pinot^ have^ investigated the early stages of^ the^ development^ of^ the^ cervical
somites. As the^ pectoral muscle^ is^ innervated^ by
cervical spinal nerves,^ it^ is not^ improbable^ that
the pectoral muscle,^ and^ even^ possibly^ the
sternum and^ the^ skeleton^ of the^ wing,^ arise^ from the cervical^ somites.^ In this^ connection^ it is^ worth noting that Fell (1939) as^ well^ as^ Chen^ (1952a,^ b) began their experiments on^ the^ origin^ of^ the sternum by a study of^ its normal^ development.
Both Fell and^ Chen^ pointed out^ that^ the^ develop-
ment of^ the^ sternal^ bands-which^ occurs^ in^ the
region where^ lateral^ plate^ mesoderm material^ is
available-is preceded^ and^ accompanied^ by
general tissue migration^ from^ the^ dorsolateral
body wall in a ventral direction.^ They^ do not
comment on the origin of^ this^ material.^ That this
may originate from somites seems^ not^ unlikely,
but experimental studies are required before^ this
question can be definitely answered.
The above-mentioned data on the embryonic
development of the sternum make it clear that
sternal anomalies^ can^ be^ divided^ into^ two^ prin-
cipal groups, as^ indicated^ by^ de^ Groot^ and
Huizinga (1954):
a. The most common type^ of^ fissure^ is^ that^ in
the cranial part of the sternum.^ Non-fusion^ of
the blastemas described as^ suprasternal^ struc-
tures and as the precostal process prevents^ the
union of the cranial ends of the sternal^ bands.
This results in a partial sternal^ fissure.^ If the
union of the sternal bands fails at full length^ this
abnormal course^ of^ development^ leads^ to^ a^ total sternal fissure.
b. Exceedingly^ rare^ is^ the^ isolated^ fissure^ in
the caudal portion of^ the^ sternum^ without other
congenital anomalies. This^ anomaly^ is^ to^ be
ascribed to premature termination^ of^ an^ other-
wise normal course of^ development^ Central
perforations in the sternal body and^ xiphoid
fissures come under^ this heading.
As congenital sternal fissures are^ rare,^ its^ thera-
peutic consequences are less well known.^ The
gravely abnormal mobility of^ the^ anterior^ chest
TABLE
OPERATIONS FOR CONGENITAL STERNAL^ FISSURE^ FROM THE LITERATURE
Patients Treated Author by Operation^ IndicationsVital No. Age Burton (1947) ..^2 7 wk^ Intermittent cyanosis 12 yr Maier and Bortone (1949) 1 2 mth^ Dyspnoea Klassen (1949) ..^1 1 dy^ - Longino and Jewett (1955) 1 6 dy^ Tachypnoea Sabiston (1958) ..^1 21 yr^ - Asp and Sulamaa (1960) (^2) 2 mth^1 dy^ Resp.circ.^ and symp- toms in both cases Keeley et^ al.^ (1960) ..^1 17 mth^ Recurrent resp. infection Chang and Davis^ (1966)^1 4 yr^ - Thompson (1961) ..^1 10 dy^ - Jewett et al. (1962). 1 6 wk^ - Martin and Helmsworth (1962) 1 8 mth^ - Ingelrans and Debeugny (1965) 1 4 wk^ - 14
A. Eijgelaar and J. H. Bijtel
FIG. 10. Sternal halves approximated; evident gain^ of^ space^ by the^ incision^ in the costal cartilage. (From Sabiston, D. C., J.^ thorac. Surg.,^ 35,^ 118, 1958.)
Diarrhoea and^ purulent^ conjunctivitis^ made^ it necessary to postpone^ the^ operation^ until^5 May^ 1967. At that time the two sternal^ halves^ were^ approxi- mated, as indicated by Sabiston^ (Figs^9 and^ 10).^ The post-operative course was uneventful apart^ from some slightly delayed healing of the wound. A few weeks later, venous congestion in the right arm was observed when the patient^ was^ resting^ on the right side (costoclavicular^ compression?).^ This venous congestion has^ not^ been^ observed^ since^ the child's discharge from the clinic. When seen^ two^ years^ after the operation^ the^ child had grown satisfactorily. The distal part of^ the sternum, however, shows an anomaly that^ causes^ a cleft-like excavation of the chest wall^ (Fig.^ 12). Probably a dissociation in^ the speed of^ the^ growth of the original caudal sternal^ bridge^ is^ the^ reason for this anomaly.
DISCUSSION
Operative correction of^ a^ sternal^ fissure,^ total^ or partial, is^ technically^ feasible^ in^ neonates^ as^ well
as in slightly older infants. In a number^ of the
14 cases listed in the Table the operation was^ per-
formed on^ a^ vital^ indication,^ e.g.,^ attacks^ of
cyanosis, dyspnoea, tachycardia^ or^ recurrent
respiratory infections (Burton,^ 1947;^ Longino
and Jewett, 1955; Martin^ and^ Helmsworth,^ 1962).
In the other patients the operative indication^ was
determined chiefly by the paradoxical movement of the anterior chest wall.^ However, the^ extent to
which an apparently paradoxical^ movement^ is
likely to^ produce vital^ symptoms^ is^ often^ un-
certain shortly after^ birth.
Attacks of cyanosis in neonates^ and^ recurrent
respiratory infections in^ somewhat^ older^ infants
constitute a vital indication^ for^ correction^ of the
anomaly. Even in^ neonates,^ determination^ of
arterial and venous^ blood^ gas^ values^ supplies^ a measurable indication^ of^ the^ influence^ of^ the
anomaly on^ respiration^ and^ circulation.
However, when a patient with^ a^ congenital cleft sternum shows no^ serious^ symptoms either shortly after birth^ or^ later, the^ necessity^ for
Congenital cleft sternum
immediately after the operation (Jewett, Butsch,
and (^) Hug, 1962 ; Ingelrans and (^) Debeugny, (^) 1965).
In the remaining 12 patients, who showed no
abnormality other than the sternal fissure, the
operative correction was successful and without
complications.
Operative correction^ of^ a^ congenital sternal fissure is therefore (^) quite justifiable even in cases in which (^) there is only paradoxical movement of the (^) anterior chest wall. It must be pointed (^) out, however, that, (^) according to^ our^ experience, there may be^ two^ additions^ to^ the^ technique described by Sabiston: (1) the^ caudal^ bridge in the sternum (^) probably
should be opened before the sternal bars are
approximated to^ prevent a^ later^ growth anomaly, as shown (^) by our (^) patient;
(2) the approximation and fixation by a few
stitches of the sternal ends of the sternocleido-
clavicular muscles may prevent a later lung hernia
through the (^) thoracic outlet (Daum and (^) Heiss, 1970).
TIMING THE OPERATION When there are (^) vital indications, such as^ attacks of tachycardia and cyanosis, it is^ obvious^ that^ the^ operation must^ be performed as soon after birth as possible. In all other cases it is advisable to operate at an (^) early
FIG 11. Chest radiograph in which the retraction (^) in age, when the 'flexibility' of the chest (^) wall Fig. 2 is outlined (^) by lead wire (^) markers.
operative correction^ remains^ a^ moot^ point. This
question is the more urgent because the literature
contains several reports on adults with a con- W
genital sternal fissure which had remained
asymptomatic (Szenes, 1922; Greig, 1926; de Groot and (^) Huizinga, (^) 1954; Meissner, (^) 1964). ' ll'. Magan (^) (1949) and Pfeiffer (^) (1956), for example, described a woman with a (^) congenital sternal
fissure who had had several uneventful preg-
nancies. The patient referred to by Pfeiffer had in
fact a total fissure. The (^) operative indication (^) in
these patients would therefore have been cos-
metic. This is not a reason to omit the (^) operation, but its risk must (^) seriously be taken into considera-
tion.
The (^) literature shows that correction of a con-
genital sternal fissure carries a small risk: 12 of
the 14 operations remained free of complications.
Two patients died after the operation, but in both
there was a complication in the form of cervico-
facial (^) angiomatosis, with (^) angiomas also in (^) the
proximal part of the trachea. Probably as a result
of the intubation, the intratracheal angiomas bled
abundantly, as a result of which the patients died FIG. 12. Two years after operation.
