- Author: Jeff Cloyd, MD; Chief Editor: Meda Raghavendra (Raghu), MD more...
The scalp is an envelope of 5 separate soft tissue layers that combine to cover the skull. It stretches from the supraorbital margins on the anterior aspect to the external occipital protuberance of the posterior aspect of the skull. It contains a thick layer of skin (within which is contained hair and sebaceous glands), connective tissue, epicranial aponeurosis, loose areolar tissue, and the pericranium.
The skin, connective tissue, and aponeurosis are bound together in one single unit that slides atop the areolar tissue. The aponeurosis comprises the underside of the skin-connective tissue unit and serves as the insertion site for the muscles of the scalp. The pericranium is a thin fascial layer fixed to the outer portion of the skull. It is continuous with the endosteum of the skull bones, so subperiosteal hematomas typically take the shape of the skull bones underlying the bleeding.
A mnemonic device for remember these layers is as follows:
S - Skin
C - Connective tissue & cutaneous vessels & nerves.
A - Aponeurosis (epicranial aponeurosis)
L - Loose areolar tissue
P - Pericranium (periosteum of skull bones) 
An image depicting scalp anatomy can be seen below.
Blood supply to the scalp comes from both the internal and external carotid arteries, and these arterioles anastomose randomly along the connective tissue plane of the scalp. Because these vessels are contained within the connective tissue, compromise of the vessels that would typically lead to vasospasm elsewhere in the body is prevented by the rigid tissue, leading to the classical large volume bleeding associated with scalp lacerations.
Nerve supply of the scalp comes from the fifth cranial nerve (trigeminal), as well as the cervical plexus. The forehead is innervated by branches of the V1 division, specifically the supraorbital and supratrochlear nerves. The vertex and lateral region of the scalp receives its nerve supply from the V2 and V3 divisions (zygomaticotemporal, and temporomandibular and auriculotemporal nerves, respectively). The posterior scalp sensation is supplied by the greater auricular and occipital nerves. All of these nerves become superficial (and accessible to anesthetic access) above an imaginary line drawn from the occipital protuberance to the eyebrows, passing along the upper border of the ear. In the scalp, the nerves travel between the connective tissue and aponeurosis.
See Scalp Anatomy for more information.
The most common reason for providing anesthesia to the scalp is repair of a laceration or foreign body removal. Although some small lacerations may not require any anesthesia to repair, most scalp lacerations can be repaired using simple local infiltration of the tissues. In pediatrics, local topical anesthesia provides sufficient blockade of pain sensation to afford reapproximation of lacerations. Other, larger lacerations, or lacerations that require fine cosmetic outcomes can be anesthetized using a regional block of the scalp by infiltrating the larger nerves supplying sensation to the injured tissue. Each of these techniques can also be used for exploration of scalp wounds and drainage of abscesses, as well.
Regional anesthesia is an excellent choice if multiple lacerations or foreign bodies (windshield glass) exist and is the preferred choice for wounds that require good cosmesis because the anesthesia is deposited distant from the wound site, preventing distortion of the wound edges.
Regional scalp anesthesia can be used to provide relief from headaches of muscular and nervous etiology, ie, occipital headaches and trigeminal or occipital neuralgia, and is an excellent choice for perioperative analgesia in both adults and children.
Very few contraindications exist to local or regional anesthesia of the scalp. Topical lidocaine should be used with great care around the eyes. Injection of local anesthetic should never be performed through infected tissue.
Scalp anesthesia can be provided using both subcutaneous injections and topical solutions. Subcutaneous injections can be short-acting, long-acting, or a combination of both, and often injections are mixed with a vasoconstricting agent to help control bleeding. An added benefit of vasoconstriction is prolongation of the anesthetic action through decreased blood flow from the site of infiltration; it is this mechanism that increases the maximum doses of anesthetic medication.
The most commonly used short-acting subcutaneous anesthetic agent is lidocaine, which can be given as 1% or 2% mixtures. Epinephrine 1:1000 may be added to both 1% and 2% solutions. Because of the high vascularity of the scalp, the use of epinephrine with wound anesthesia is usually considered safe. The time of injection to onset of anesthesia with lidocaine is approximately 60-90 seconds, and the effects of lidocaine typically last 20-30 minutes (up to 2 hours if mixed with epinephrine). The maximum dose of lidocaine in adults is 300 mg (3-4 mg/kg in children), when mixed with epinephrine, the maximum dose is 500 mg (7 mg/kg).
Common long-acting anesthetic agents include Sensorcaine, 0.25% or 0.5% bupivacaine (Marcaine). The time of onset of these long-acting agents is approximately 10-20 minutes, but the anesthetic effects last 4-6 hours alone, and up to 8 hours when mixed with epinephrine. The maximum dose of bupivacaine is 175 mg (2mg/kg) in an adult, but this is increased to 225 mg (3mg/kg) when mixed with epinephrine.
50/50 mixtures of lidocaine and bupivacaine may provide the most optimal anesthetic for certain lacerations, providing nearly immediate relief from pain from the short-acting component, and providing many upwards of 8 hours of anesthesia from the long-acting medication.
LET and EMLA solutions and creams are preparations that have been developed and approved for the anesthesia of superficial wounds and intact skin. They have proven to be the most advantageous in children, where a topical application before injection lessens the discomfort of an already scary procedure. LET is a combination of lidocaine 4%, epinephrine 1:1000, and tetracaine 0.5%; EMLA is lidocaine 2.5% and prilocaine 2.5%.
Table. Dosing for the Most Common Short-Acting and Long-Acting Local Anesthetic Agents (Open Table in a new window)
|Lidocaine||300 mg||3 - 4 mg/kg|
|Lidocaine with epinephrine||500 mg||7 mg/kg|
|Bupivacaine||175 mg||2 mg/kg|
|Bupivacaine with epinephrine||225 mg||3 mg/kg|
All injections should be performed under sterile conditions, with the area of injection cleaned with iodine or chlorhexidine. The size of the syringe varies depending on the amount of anesthetic given (keep in mind maximum doses), but all injections should be given with the smallest needle possible in an effort to cause the least pain. A 25-gauge needle is small enough to provide little trauma to the skin and is an excellent choice for administration of anesthesia.
Clippers may be necessary to remove hair that is within the wound site or obstructing wound repair. No benefit to shaving the skin around the wound edge has been proven, and this practice should be avoided.
Preparation for scalp anesthesia is the same as for repair of laceration or drainage of an abscess. The patient should be in a comfortable position as the procedure may take some time depending on the magnitude of the procedure. The patient should also be positioned in such a way as to make the person administering the medication as comfortable as possible. Injections should be given under good lighting to ensure accuracy and safety from accidental needle sticks.
For wounds on the forehead, vertex, or temporal regions of the scalp, the patient should lie supine on a stretcher with the head of the bed positioned between 30 and 45 degrees. The bed should be elevated as high as possible to bring the wound site just below eye level for the practitioner.
Patients with wounds to the posterior region of the skull and injections to treat occipital headaches should be positioned in the seated position, with the bed lowered as far as possible. The practitioner may then stand behind the patient and administer anesthesia. Another option for posterior scalp access is to have the patient lay on their side on a bed with the head lowered all the way. This manner may be more appropriate for patients who have lost a significant amount of blood, or who complain of dizziness or vertigo.
For all injections of anesthetic, the skin should be thoroughly cleaned with iodine or chlorhexidine and the practitioner should wear sterile gloves.
Topical anesthetic is most commonly used in the pediatric patient because good anesthesia can be achieved without ever inserting a needle through the skin. It is easily placed over the wound or site of incision and then covered with a waterproof, occlusive dressing (such as Tegaderm). The medicated dressing is left for 30 minutes and then removed along with the excess gel. If patients still do not have full anesthesia, a local anesthesia may also be given through the already anesthetized site with minimal discomfort. Care must be taken with topical anesthetic to prevent contact with the eyes.
To anesthetize a laceration, first clean and sterilize the wound as tolerated by the patient. Lacerated wounds are best anesthetized by passing the needle directly into the subcutaneous tissue through the open laceration, thereby avoiding the creation of a new break in the skin. A wheal should be created on both sides of the wound.
When anesthetizing for drainage of an abscess, the perimeter of the site to be incised can be fully covered through 3 injection sites in a triangular shape. Insert a 25-gauge needle into the skin and then track along the perimeter, injecting as the needle moves through the subcutaneous tissue. The needle can then be retracted until almost out of the skin, and the direction can be changed, the needle passed along the other side of the abscess while injecting, and then removed from the skin. Move 120 º around the abscess, repeat, then move another 120 º and repeat once more.[5, 4]
Ophthalmic nerve block (anterior scalp)
The nerves of the ophthalmic branch, including the supraorbital, supratrochlear, and infratrochlear nerves, are all anesthetized at the point where they exit the skull — the supraorbital notch. The supraorbital notch can be palpated on the ridge of the upper orbital bone in line with the patient’s pupil (when looking straight forward). Insert a 25-gauge needle attached to a syringe at the supraorbital notch.
Sensations of electrical shock in the forehead indicate that the needle is in the appropriate location. Using a finger or gauze roll, place pressure on the underside of the superior orbital bone to prevent the anesthetic from draining into the upper eyelid. Carefully aspirate, and then inject between 1 mL and 3 mL of anesthetic (see image below). If the patient does not receive adequate analgesia with this single injection, several small injections can be placed along the superior orbital rim.
Greater and lesser occipital nerve block (posterior scalp)
For greater occipital nerve anesthesia (see the image below), palpate the occipital protuberance and mastoid process — the occipital artery runs through the scalp at this point (may or may not be palpable, depending on body habitus). Using a 25-gauge needle attached to a syringe, insert the needle just medial to the occipital artery. Carefully aspirate to ensure needle tip is not in the occipital artery, and then inject 5 mL of anesthetic. To anesthetize the lesser occipital nerve, remove the needle from the skin and move 3 cm laterally and 1 cm caudally. Insert the needle (again aspirating to prevent intra-arterial injection), and inject another 5 mL of anesthetic in a semi-circular or fanlike pattern.
Anesthesia of the scalp requires only very superficial injection, and deep injection not only does not provide adequate anesthesia, but may actually cause increased bleeding.
Unless the wound is grossly contaminated, anesthetic should be injected into the subcutaneous tissue through the wound edge, directly into the subcutaneous fat. If a 25-gauge needle is advanced slowly, patients will not feel the needle passing through the tissue, and the surrounding skin will be left intact (protecting from infection).
Warming anesthesia medications prior to injection reduces the discomfort and "burning" sensation reported by patients. Cooling of the site to be injected prior to administration also has beneficial effects with regards to injection discomfort. Before anesthetizing, place an ice pack over the wound and run the medication under hot water in the sink while washing your hands.
The most common complication associated with scalp anesthesia is hematoma formation at the site of injection. Swelling of the upper eyelid and ecchymosis around the orbit are also possible with injections in the frontal region secondary to blood and fluids traveling along the aponeurosis (see Overview).
Another potential complication to scalp anesthesia is overdose, and proper dosing of medications is the most efficient method for preventing toxicity. The maximum doses for commonly used medications can be found in the Anesthesia section. During the procedure, toxicity can also be avoided by carefully aspirating the syringe before injection to ensure the tip of the needle is not in an artery or vein.
Allergic reactions, infection, and failure to anesthetize the appropriate region are also complications from attempted anesthesia.
(Public Domain). Grey's Anatomy Scalp Diagram. Alchemipedia. Available at http://alchemipedia.blogspot.com/2010/01/scalp-layers-anatomy-mnemonic.html. Accessed: 4/4/2011.
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