Evaluating the SXR in an infant or toddler presents unique problems. Diagnostic confusion between sutures and fractures may have serious consequences. A basic understanding of the locations and variable appearances of these sutures will help to reduce the likelihood of misdiagnosis⁴^–⁸.

A basic classification of skull sutures in infants and toddlers

Grouping	Notes	Sutures
The normal sutures	Visible on the SXR in all infants and toddlers – persisting in all adults	Sagittal, coronal, lambdoid, squamosal, and smaller sutures around the mastoid
A normal developmental suture	Visible on the SXR in all infants and many toddlers – but not in adults	Innominate
The most common accessory sutures	Visible on the SXR in some infants and toddlers – occasionally persisting to adulthood	Metopic, accessory parietal, mendosal

Normal accessory sutures and the radiographs on which they are seen

Suture	Most commonly seen on	Notes
Metopic suture	Frontal √ √ Towne’s √	The commonest accessory suture. It is also the one that most commonly persists in older children, and even in a few adults.
Accessory parietal suture	Towne’s √ √ Frontal √ Lateral √	May be complete or incomplete. Occurs in vertical, horizontal or oblique orientations. Most commonly vertical.
Mendosal suture	Lateral √ √ Towne’s √	Extends posteriorly from the lambdoid suture on the lateral view. Passes medially on Towne’s view.
Innominate suture	Lateral √ √	Sometimes classified as an accessory suture but best regarded as a normal developmental suture because it is always present in infants. As the child matures this suture disappears.

The lateral SXR

The normal sutures. L = lambdoid suture; C = coronal suture; M = mendosal; O = occipitomastoid suture; Sq = squamosal suture; In = innominate suture

Accessory parietal sutures. Can appear in various positions (P).

Accessory parietal sutures vary in position. This drawing does not correspond to any radiographic projection. It shows the general positions and direction of the more common incomplete accessory parietal sutures (P1 and P2) when looking down from above the cranium.

L = lambdoid suture;

C = coronal suture;

Sa = sagittal suture;

P = accessory parietal sutures.

The AP frontal SXR

Normal sutures on the frontal view.

L = lambdoid suture;

C = coronal suture;

Sa = sagittal suture;

Sq = squamosal suture.

Accessory suture—the metopic.

This suture divides the frontal bone into two halves.

Met = metopic suture.

Accessory parietal sutures.

The drawing shows possible positions/sites of accessory parietal sutures.

L = lambdoid suture;

Sa = sagittal suture;

Sq = squamosal suture;

P = accessory parietal suture.

The Towne’s SXR

Normal sutures on the Towne’s view.

L = lambdoid suture;

C = coronal suture;

Sa = sagittal suture;

Sq = squamosal suture;

FM = foramen magnum.

Accessory suture—the mendosal.

This accessory suture is situated in the occipital bone. Very occasionally it is whole (ie complete). More often it is incomplete. Very often it is incomplete and on one side of the bone only.

M = mendosal suture;

L = lambdoid suture;

Sq = squamosal suture;

FM = foramen magnum.

Analysis: suture recognition

The principal question: is it a suture or a fracture?⁴^–⁸

When assessing suspected non-accidental injury (NAI) in young children, be very careful not to rush too swiftly to judgement. Observing an abnormality is important. An informed approach is then required when assigning a particular significance to the abnormality⁹^–¹².

Be aware …

▪ Wide sutures are normal in neonates.

▪ Accessory sutures are common and are a part of normal development. An awareness of the positions and appearances of the common accessory sutures will help to reduce errors of interpretation.

▪ The age at which an accessory suture closes is variable. Accessory sutures are present in some older children. Very occasionally they persist into adulthood.

▪ Radiography in a wriggling infant can be very difficult. The Towne’s view (injury to occiput) or the AP frontal view (injury elsewhere) is frequently a technical compromise. The head is often slightly rotated.

Assessing the radiographs

1. Trace every line seen on the two standard radiographs. For each line ask yourself: is this a suture?

2. Whenever a lucent line is detected it is essential to assess the two radiographs together. They form a complementary pair.

3. Always correlate the findings with the clinical history and the physical examination.

The importance of evaluating the two SXR views as a pair. On the frontal SXR (left) the lucent line (arrow) could be interpreted as an accessory suture. The lateral view (right) shows that the line (arrow) is much more extensive and continues through to the temporal bone. This is a fracture.

Suture recognition on the Towne’s view

Normal sutures present in all children.

Towne’s view.

L = lambdoid suture;

C = coronal suture;

Sa = sagittal suture.

Mendosal suture. A mendosal suture (arrow) can be present on both sides. It may be complete or incomplete. Most commonly it is incomplete. M = mendosal suture; L = lambdoid suture; Sq = squamosal suture; FM = foramen magnum.

Suture recognition on the lateral view

Lateral view.

L = lambdoid suture;

C = coronal suture;

O = occipitomastoid suture;

Sq = squamosal suture;

In = innominate suture.

The sagittal and metopic sutures are not seen on the lateral view because they lie in the midline (ie parallel to the plane of the radiograph).

Squamosal suture. Extends anteriorly, separating the parietal bone from the temporal bone. The usual appearance is of a pair of lines (arrows) on the lateral projection (ie the left squamosal suture and the right squamosal suture). Invariably, the squamosal suture fades away as it passes anteriorly.

Lambdoid suture. As it nears the base of the skull (in the region of the mastoid bone) the suture appears to be complex. This seemingly tangled appearance is mainly caused by overlapping of the normal occipitomastoid sutures on the right and left sides. Don’t worry about this. Arising from the lambdoid suture there will be:

▪ a normal suture, the squamosal suture.

▪ a normal developmental suture, the innominate suture.

▪ sometimes, an accessory suture, the mendosal suture.

Accessory parietal sutures (also known as intraparietal sutures).

These are often best seen (arrow) on this view.

Suture recognition on the AP view

The sagittal and lambdoid sutures are well shown. In addition an accessory parietal suture (arrow) is also present.

The lambdoid suture meets the sagittal suture in the midline.

On the frontal radiograph the sagittal suture appears foreshortened.

Normal sutures on the frontal view.

This diagram also shows wormian bones contained within the lambdoid sutures.

L = lambdoid suture;

C = coronal suture;

Sa = sagittal suture;

Sq = squamosal suture;

W = wormian bone.

Wormian bones.

It is not uncommon to see one (or several) wormian bones (W) on the AP projection, and occasionially also on other projections. This is a normal finding. A wormian bone is a small area of the skull (sometimes as large as 1–2 cm in diameter) within a suture. The bone is completely surrounded by the lucent suture.

Metopic suture.

Where it meets the coronal suture, the sagittal suture should stop. If it continues below this point then the patient has a metopic suture. This accessory suture divides the frontal bone into two halves. The metopic suture (arrow) is the commonest accessory suture in children. Sometimes it persists into adulthood. Note the wormian bone in the sagittal suture and another in the left lambdoid suture.

Accessory parietal suture.

Accessory parietal sutures are not exceptional. Of all the accessory sutures these are the ones that cause the most confusion.

Accessory parietal sutures may be complete or incomplete. They may be visualised on the frontal (arrow) and/or the lateral projections.

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Paediatric skull—suspected NAI

Paediatric skull—suspected NAI

Normal anatomy