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Embryonic Sternum Development & Formation of Cleft Sternum, Study notes of Literature

An in-depth analysis of the embryonic development of the sternum and explains the pathogenesis of cleft sternum (fissura sterni congenita), a rare congenital anomaly. the layers of the embryo, the formation of the coelom, and the development of the ventral body wall, highlighting the role of the somites and the formation of the sternum. The document also explores the origin of the precostal process and the development of the manubrium, as well as the therapeutic consequences of congenital sternal fissures.

What you will learn

  • What are the stages of embryonic development that lead to the formation of a cleft sternum?
  • What is the role of the somites in the development of the sternum?
  • How does the formation of the coelom contribute to the development of a cleft sternum?

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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;
4.
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
490
..-.
-
-
.
-
-.--.-C,
--,
-
----
--
pf3
pf4
pf5
pf8
pf9

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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;

  1. 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.