Paediatric anatomyAnthony Lander

Jeremy Newman

ences

and

can assume any position and still develop normally. In prema-

o the

hers.

ates,

in adult intercostals and diaphragms, are not prominent until

BASIC SCIENCEAnthony Lander FRCS(Paed) is a Consultant Paediatric Surgeon at the

Birmingham Childrens Hospital, Birmingham, UK. Conflicts of interest:

none declared.

Jeremy Newman FRCS is a Vascular Surgery Registrar at the Worcester

Royal Infirmary, Worcester, UK. Conflicts of interest: none declared.ture babies, malleable developing bones, especially the skull,

may become distorted due to gravity, pressure from mattresses

or medical equipment. The normal skull is approximately

circular in cross-section, whereas many premature skulls develop

elliptical cross-sections. This can mean that measurements of

head circumference, used as a surrogate for brain volume, may

overestimate volume. Head circumference is serially measured,

as an abnormally enlarging head could indicate the development

of hydrocephalous after a bleed for example. Poor head growth

may indicate poor nutrition or neurological impairment.

The bones of all children have an important haematopoietic

function, which in adults is limited to the red marrow of the ribs,

sternum, vertebrae and proximal ends of the humerus and femur.

Fontanelles

Ossification has not reached the suture lines of the skull at birth

and the junctions between the calvarial bones are known as

fontanelles. Of the six normally present, the anterior is the largest

and transmits the pulsation of the sagittal dural venous sinus,

which it overlies. The paired sphenoid and posterior are closed

by 6 months and the paired mastoid and anterior by 2 years of

age. During parturition the calvarial bones of the neurocranium

are displaced and may even overlap at the suture lines to allow

passage of the head through the birth canal.

Vertebral column

At birth the spinal column is very flexible and lacks the fixed

curvatures present in adulthood. The thoracic curvature developsBefore birth the fetus is weightless within the amniotic sacbetween adults, infants and neonates is essential for the clinician

managing newborns. This article illustrates the clinically important varia-

tions in anatomy, focussing mainly on the normal neonatal anatomy.

Keywords Anatomy; development; infant; neonate

Musculoskeletal systemthe successful management of the preterm infant born at as early

weeks gestation. An understanding of the anatomical differAbstractTechnological and clinical advances in neonatal medicine have enabled

as 24SURGERY 31:3 101The large tongue is short and broad, lying entirely within the oral

cavity. It begins to descend into the neck during the first year of

life, the posterior third forming part of the anterior wall of the

pharynx by age 4 years. During suckling the high position ofOral cavityabout 2 years of age. The thymus is a large structure in the first

year of life and easily causes confusion on chest X-rays.

Gastrointestinal system (Figure 1)child. The type 1 muscle fibres, which are fatigue resistant,leading to a higher rate of respiratory failure. This may be treated

with the administration of surfactants.

Thorax (Figure 1)

The neonatal thorax has a rounder circumference when

compared to the adult more flattened appearance. It is very

compliant and susceptible to collapse during negative intratho-

racic pressure. The work of breathing is thus much greater in the

seenthe alveoli. At term airway patency is maintained by su

active proteins, which are deficient in premature neonThe trachea is short and the cricoid cartilage is the narrowest

point of the airway in children under 5 years of age. Uncuffed

endotracheal tubes can be used to intubate children under the

age of 12 years, forming a good seal at the cricoid ring. The

thyroid cartilage is shorter and broader in the child and lies

nearer the hyoid and its superior notch and laryngeal prominence

are less marked. The sexual differences in the larynx are evident

by 3 years of age. The trachea is relatively soft in the first year of

life and is easily compressed.

Respiratory system

Alveoli continue to increase in number and size until around 8

years of age. Growth beyond this is seen in both the airways and

rfaceand the trachea and neck are short. Due to these differe

children up to the age of 5 years may be obligate nasal breatRespiratory system

Airway

The tongue is relatively large and the nares small, in comparison

with an adult. The larynx is anterior and cephalad (C3-4 vs C6)

nces,developed at this stage, giving a rather flat appearance t

buttocks.These are well developed and long compared to the neonatal

lower limbs. The elbow is unable to fully extend at birth by about

15. The neonate has a relatively strong grasp reflex and is ableto support its own weight within the first days of life.

Lower limbs

These are under-developed and remain in a flexed and abducted

position in the neonate. They appear bowed due to the relative

immaturity of the medial head of gastrocnemius compared with

the lateral. The general musculature for walking is also not wellUpper limbsfirst, being concave anteriorly. The cervical develops at around

3 months when the child is able to support the weight of its head

and the lumbar when learning to walk at about 1 year. 2013 Elsevier Ltd. All rights reserved.

than

BASIC SCIENCEthe larynx is elevated further so that the fluid passes directly into

the pharynx. This enables the infant to feed and breathe at theFigure 1falciform ligamentLarge liver

horizontal diaphragm

Umbilical vein andRelatively flatLarge thymus

Abdomen and chestsame time.

Oesophagus

At birth the oesophagus is approximately 8e10 cm long and

extends from the cricoid cartilage to the gastric cardia (C4 to T9)

and possesses the same constrictions as that of the adult. The

adult oesophagus starts and finishes two vertebral bodies lower

(C6 to T11).

Abdomen

In the adult the abdomen is generally rectangular with the long

axis vertical and the most common open surgical approaches are

made through vertical incisions. In babies the abdomen is

broader than it is long and open procedures are generally made

through transverse supraumbilical incisions.

Stomach

The stomach is very small at birth and lies under the liver. If

a gastrostomy is needed its placement may not be easy in the first

few days of life. This is particularly so if there is no antenatal

swallowing in the case of an isolated oesophageal atresia, when

the stomach may be less than 5 ml in volume. The stomach

distends fivefold in the first few days once swallowing and feeds

commence. Acid secretion begins during the first day of life. The

stomachs anterior surface is nearly entirely covered by the left

lobe of the liver, only a small portion of the greater curvature

being visible below. Its size increases rapidly from 30 ml in

a term baby to 100 ml by the fourth week. An adults stomach

has a capacity of approximately 1 litre.

SURGERY 31:3 102Small and large intestine

The small intestine has fewer and less marked circular foldsLateral umbilical fold (inferiorepigastrics)

Medial umbilical fold (umbilicalartery)

Urachusof liverSmall stomach under left lobe are seen in adults. The mesentery contains very little fat and is

much easier to manage when resecting intestine than in adults.

The small intestine is between 300 and 350 cm long in a term

baby. This is a measurement with the bowel under gentle tension

and the mesentery removed. At a laparotomy with normal

smooth muscle tone and a normal mesentery the small intestine

appears closer to 120 cm than 300. The small intestine lies in

a more transverse orientation than in the adult due to the

abdominal bladder. The large intestine is approximately 60 cm

long and has a very poorly developed muscularis. The ascending

and descending colon are relatively short and the transverse

colon relatively longer. The normal haustra and appendices

epiploicae are not present, giving it a very smooth outline. The

haustra appear over the first 6 months.

Liver

The liver is relatively large in the neonate being 4% of body

weight compared to the adult where it constitutes only 2.5e3%.

The right lobe extends below the costal margin anteriorly and lies

close to the iliac crest posteriorly. The left lobe can extend to the

lateral wall of the abdomen, overlying the stomach and the

spleen.

Gallbladder

The gallbladder does not extend to the edge of the liver and has

a small peritoneal surface. The majority are embedded within the

liver. After the second year of life it has proportionately similar

characteristics to an adult. It is easy to miss the gallbladder at

2013 Elsevier Ltd. All rights reserved.

a neonatal laparotomy, but its presence should be documented

since an absent gallbladder is associatedwith some rare anomalies.

Pancreas

The pancreas has a relatively large head and its body points

upwards and to the left towards the tail.

Peritoneal cavity

The anterior abdominal wall bulges forwards in the neonate to

accommodate the bladder, uterus and ovaries, which are pelvic

in the adult. This is accentuated by the flattened diaphragm

pushing down on the supracolic compartment.

Genitourinary system (Figures 2 and 3)

The kidneys

The kidneys are lobulated at birth, have wide-calibre ureters and

lie under relatively large adrenal glands.

Bladder

The apex of the unfilled bladder lies midway between the pubis

and the umbilicus and, when filled, may reach the umbilicus.

Only the posterior surface is covered with peritoneum and,

although considered intra-abdominal, about half lies within the

pelvic cavity. It does not truly become pelvic until about the sixth

million or so remaining at birth, only about 400 will actually

ovulate.

Uterus

The uterus is influenced by the maternal hormones during fetal

development and so usually decreases by about a third in size

after birth until puberty is reached. At birth it is approximately

2.5e5 cm long and 2 cm wide, the uterine cervix accounting for

two-thirds of this. Occasionally the early response to the with-

drawal of maternal hormones is accompanied by a small uterine

bleed.

Testes

The testes are situated at the deep ring by the sixth month of

gestation and 98% in term babies and 80% in preterm babies will

have descended into the scrotum by birth. The processus vagi-

nalis is collapsed at birth, but not necessarily obliterated. Eighty

percent are obliterated 10e20 days after birth. Undescended

testes are a common surgical problem and if a testis has not

descended to the scrotum by 3 months of age surgical referral is

essential and an orchidopexy is typically performed around 1

year of age.

Inguinal canals

The inguinal canal is similar to the adult and it is rarely true that

ough

lar

BASIC SCIENCEFigure 2Right gonadal vesselsLarge adrenalsInferior vena cavaOvaries

The ovaries are much larger than the testes at birth and weigh

approximately 0.3 g. They lie in the iliac fossae at birth and

descend into their pelvic position in early childhood. All the

primary oocytes are present after the first trimester. Of the 1

Lobulated newborn kidneys andThis may rarely be patent and leak urine.year of life. The ureters correspondingly do not have a pelvic

component until that time also. The top of the bladder is

continuous with the urachal remnant (median umbilical ligament

and the overlying median umbilical fold) reaching the umbilicus.SURGERY 31:3 103Left gonadal vesselsge adrenalsa small opening in the front of the canal is possible. The canal is

short, but so are the arms and legs!

Cardiovascular system

Heart

At birth the right ventricle has been working against systemic

pressure and the muscular bulk is therefore only 25% smalleringuinal hernias the canal has some length and a repair thrthe internal and external rings overlap e this is a common

misconception. Even in small premature neonates with large 2013 Elsevier Ltd. All rights reserved.

BASIC SCIENCEStraighter anorectal angle than in an adultPelvic anatomy

Ovary in the iliac fossa

Prominent uterus at birththan the left. However after birth, when the fetal circulation

changes and pulmonary circulation is established, the left

ventricle rapidly grows and its muscular bulk becomes about

twice of the right at 2 years of age. This difference continues into

adulthood. The ventricular volumes in a heart with normal

connections are of course very similar.

Foramen ovale

This lies at the level of the third intercostal space between the

right atrium and left atrium. It is approximately 5 mm vertically

by 4 mm wide in size and allows blood to bypass the pulmonary

circulation in the fetus. Once respiration starts and the pulmo-

nary circulation is established it functionally closes. It is oblit-

erated in 3% of infants by 2 weeks and 90% by 16 weeks.

Ductus arteriosus

The ductus arteriosus, roughly 8e12 mm long, bypasses the

pulmonary trunk to the arch of the aorta in the fetus. It arises

as a direct continuation of the pulmonary trunk at the point it

divides into left and right pulmonary arteries. Its diameter is

approximately the same size as the ascending aorta (5 mm)

and joins the descending aorta just below the left subclavian

artery.

Like the umbilical artery and vein which also occlude after

birth, the wall of the ductus arteriosus is populated by smooth

muscle, connective tissue and elastic fibres which proliferate close

to birth. Bradykinin is released by the lungs on adequate exposure

to oxygen and from the umbilical cord when the temperature

Figure 3

SURGERY 31:3 104Up to 2% of testes may be undescended at birth, 0.8% by 1 yearat birth96% of foreskinsadherent to glansApex of bladder lies highdrops after birth. This causes constriction of the ductus arteriosus

and the umbilical vein and artery. Occasionally the duct remains

patent and problematic. If closure does not follow drugs such as

indomethacin or a surgical ligation may be needed.

Umbilical arteries

These are a direct continuation of the internal iliac arteries. At

birth the smooth muscle in the wall constricts and the arteries are

obliterated. The remnants of these arteries become the medial

umbilical ligaments seen on the undersurface of the anterior

abdominal wall covered by the medial umbilical folds. For

completeness remember that more lateral, still, are the lateral

umbilical folds overlying the inferior epigastric vessels (see

Figure 1).

Umbilical vein

This passes from the umbilicus, within the falciform ligament,

superiorly and to the right for 2e3 cm to the porta hepatis. It

gives off several branches to the liver before joining the portal

vein. It also contracts after birth and its remnant is the liga-

mentum teres.

Ductus venosus

Before birth the ductus venosus shunts most of the umbilical

venous blood into the inferior vena cava allowing oxygenated

blood to bypass the liver. The ductus venosus closes during the

first week of life in term neonates but may take longer to close

in pre-term babies. The remnant of the ductus is the

2013 Elsevier Ltd. All rights reserved.

ligamentum venosum. The ductus can be used for venous

access in the newborn.

Lymphatic system

Lymphoid tissue is in abundance in the neonate and continues to

increase throughout childhood.

Thymus

This weighs approximately 10 g at birth and continues to

increase in size until puberty, when it weighs about 30 g. It

decreases in adulthood and weighs about 12 g in old age. It lies in

the anterior mediastinum overlying the great vessels of the

superior mediastinum and may reach up into the cervical region

as far as the thyroid gland.

Spleen

Accessory spleens are very common in the neonate and usually

found in the greater omentum.

Summary

The anatomical and mechanical differences that distinguish

babies and children from adults have implications for the

management of the airway and surgical approaches to the

abdomen. Some of the differences that persist into infancy and

early childhood also affect the response to trauma and have

implications for trauma management. A

FURTHER READING

Advanced trauma life support for doctors, 8th edn. American College of

Surgeons, 2009.

Advanced paediatric life support, 4th edn. American Academy of Pediat-

rics, 2009.

Grays anatomy: the anatomical basis of medicine and surgery, 38th edn

(British Edition). Edinburgh: Churchill Livingstone, 2009.

BASIC SCIENCESURGERY 31:3 105 2013 Elsevier Ltd. All rights reserved.

Paediatric anatomyMusculoskeletal systemFontanellesVertebral columnUpper limbsLower limbs

Respiratory systemAirwayRespiratory systemThorax (Figure 1)

Gastrointestinal system (Figure 1)Oral cavityOesophagusAbdomenStomachSmall and large intestineLiverGallbladderPancreasPeritoneal cavity

Genitourinary system (Figures 2 and 3)The kidneysBladderOvariesUterusTestesInguinal canals

Cardiovascular systemHeartForamen ovaleDuctus arteriosusUmbilical arteriesUmbilical veinDuctus venosus

Lymphatic systemThymusSpleen

SummaryFurther reading