Clinical anatomy of scalp

 

Why deep transverse wounds of scalp tend to gape, but not longitudinal wound?

 In deep wounds of scalp if the epicranial aponeurosis is cut transversly the wounds tend to gape because the aponeurosis is under tension in anteroposterior direction due to the tone of occipitofrontalis muscle. If the wound cuts longitudinally along the direction of fibers of the aponeurosis which is directed antereoposteriorly, so it will not create large gape.  

Why scalp wounds bleed profusely – explain anatomically?

Deep lacerations to the scalp tend to bleed profusely for several reasons.

These are:

1.      Rich Blood Supply and Adherent Blood Vessel Walls: The scalp has a large number of arteries, veins, and capillaries that provide blood to the tissues. Compared to blood vessels in other parts of the body, these blood vessels in the scalp are less mobile because they are embedded in the fibrous connective tissue. A scalp wound prevents the arteries from properly retracting or constricting, which results in prolonged bleeding.

2.     Occipitofrontalis Muscle: The muscle covering the top of the skull is called the occipitofrontalis muscle, or epicranial aponeurosis. It is a thin, broad muscle. It is divided into the frontal belly and the occipital belly, which are joined by a central tendon. This muscle is in charge of making the forehead wrinkled and lifting the eyebrows. Because of its adherence to the scalp's epidermis, it may impede a wound's natural healing process, thereby intensifying bleeding.

3.     Anastomoses: Numerous arterial anastomoses, or connections between arteries that permit blood to flow from one vessel to another, are characteristics of the scalp's blood supply. In the event of a compromised vascular, these anastomoses offer alternative pathways for blood flow. Under normal circumstances, this redundancy helps with tissue perfusion; nevertheless, when a scalp injury occurs, it also leads to excessive bleeding.

Why 4^th layer of scalp (loose areolar tissue) is known as ‘dangerous layer of scalp’-explain anatomically?

The sub-aponeurotic loose areolar connective tissue layer is known as dangerous layer of scalp because the blood and pus tend to collect in this layer and as it contains the emissary veins (which connect veins of scalp to intracranial dural venous sinuses), the infection from this layer may travel readily along the emissary veins into the intracranial venous sinuses.

Why a blow on head may cause ‘Black Eye”-explain anatomically?

A  blow on head leads to collection of blood in the 4^th layer  (loose areolar tissue) of scalp. The blood from this layer may gravitate into the eyelids because the frontalis muscle has no bony attachment. This leads to formation of hematoma and black discoloration of skin around the eyes few hours after the head injury resulting in a condition called ‘black eye’. The blood cannot pass laterally or posteriorly due to the attachment of  epicranial aponeurosis and occipitalis muscle to the superficial temporal lines and superior nuchal lines respectively.

Why 4^th layer of scalp known as safety valve hematoma-explain anatomically?

In children the fracture of cranial vault may be accompanied by torn dura mater and pericranium. In such cases the blood from intracranial hemorrhage escapes into the subaponeurotic/fourth layer of the scalp through the fracture lines. As a result, the signs of cerebral compression are not seen until the subaponeurotic space is completely full of blood. Because of this the collection of blood in the fourth layer is referred to as a safety valve hematoma.

Explain anatomical basis of cephalhematoma

Accumulation of blood deep to the pericranium/periosteal layer of scalp due to injury is known as cephalhematoma. The swelling  is localized over the particular bone and takes the shape of the bone involved, because  the pericranium is loosely attached over the bones except at the sutural lines where it is connected to the endosteum via sutural ligaments. The hematoma is bound by suture lines  and the swelling has well-defined margins. Cephalhematoma is often seen in the parietal region. It may take 4-7 days to disappear.

Explain anatomical basis of caput succedaneum: It is a collection of fluid in the loose areolar tissue/fourth layer of the scalp.  The swelling is diffuse, crosses the sutures and the midlne and is over the presenting part of the head at delivery.  It  occurs  due to obstruction of venous return of scalp during the passage of head via the birth canal. Usually the edema subsides in  24-48 hrs.