Subaponeurotic Space

aponeurotica and skull (subaponeurotic space) Lumpy clot, "black eye"

^ Figure 20-3. (A) Epidural, (B) Subdural, (Cand D) Subarachnoid, and (£) Extracranial hemorrhages. In a clinical vignette question, first identify the clinical features mentioned in the question, then match the features with the appropriate blood vessel and hemorrhage (table), and finally identify the correct CT scan. ACo = anterior communicating artery (most common site for a berry aneurysm); Ar- arachnoid; B = bridging vein; Be = berry (congenital) aneurysm; CV = cerebral vein; Dl = diploic vein; Du = dura mater; EM = emissary vein; F = falx cerebri; G = galea aponeurotica; /= inferior sagittal sinus; ME = middle meningeal artery; P= periosteum; S= superior sagittal sinus; SK = skull; SN = skin. The arrow in D shows thickening of the falx cerebri. (A and B adapted with permission from Levy RC, Hawkins H, Barsan WG: Radiology in Emergency Medicine. St. Louis, CV Mosby, 1986, pp 36, 38; C reprinted with permission from Freedman M: Clinical Imaging: An Introduction to the Role of Imaging in Clinical Practice. New York, Churchill Livingstone, 1988, p 575; and D reprinted with permission from Eisenberg RL: Diagnostic Imaging in Surgery. New York, McGraw-Hill, 1987, p 608.)

Subaponeurotic Space

Figure 20-4. (A) Lateral aspect of the neck, showing the cervical triangles and their contents. Note that the common carotid artery, internal jugular vein, and CN X all lie within the carotid sheath. (B) Stellate ganglion, (C) cervical plexus, and (D) brachial plexus nerve blocks are shown. CL = clavicle; DA = digastric muscle (anterior belly); DP = digastric muscle (posterior belly); OM= omohyoid muscle (inferior belly); P= platysma; SCM= sternocleidomastoid muscle; SH = sternohyoid muscle; TR = trapezius muscle. (B, C, and D reprinted with permission from Scott DB: Techniques of Regional Anaesthesia. Stamford, CT, Appleton & Lange, 1989, pp 77, 93, 209).

Figure 20-4. (A) Lateral aspect of the neck, showing the cervical triangles and their contents. Note that the common carotid artery, internal jugular vein, and CN X all lie within the carotid sheath. (B) Stellate ganglion, (C) cervical plexus, and (D) brachial plexus nerve blocks are shown. CL = clavicle; DA = digastric muscle (anterior belly); DP = digastric muscle (posterior belly); OM= omohyoid muscle (inferior belly); P= platysma; SCM= sternocleidomastoid muscle; SH = sternohyoid muscle; TR = trapezius muscle. (B, C, and D reprinted with permission from Scott DB: Techniques of Regional Anaesthesia. Stamford, CT, Appleton & Lange, 1989, pp 77, 93, 209).

Anterior (carotid) A Contents

• Common carotid artery

• Internal jugular vein

• Ansa cervicalis

• Sympathetic trunk

(stellate ganglion nerve block)

Posterior (occipital) A Contents

• Subclavian artery

• External jugular vein

• Cervical plexus (nerve block)

• Brachial plexus trunks (nerve block)

brachial plexus and subclavian artery enter the posterior (occipital) triangle in an area that is bounded anteriorly by the anterior scalene muscle, posteriorly by the middle scalene muscle, and inferiorly by the first rib.

d. Enlarged supraclavicular lymph nodes as a result of upper gastrointestinal or lung cancer may be palpated in the posterior (occipital) triangle.

e. Cervical plexus nerve block is used for superficial surgery on the neck or thyroid gland. The needle is inserted at vertebral level C3, along a landmark line that connects the mastoid process to the transverse process of C6.

f. Brachial plexus nerve block. The needle is inserted into the interscalene groove (between the anterior and middle scalene muscles) at vertebral level C6. The cricoid cartilage (C6) and sternocleidomastoid muscle are used as landmarks.

III. LARYNX (Figure 20-5)

A. General features. The larynx consists of five major cartilages: the cricoid, thyroid, epiglottis, and two arytenoid cartilages. The ventricle of the larynx is bounded superiorly by the vestibular folds (false vocal cords) and inferiorly by the vocal folds

Location Vocal CordsLateral Views Arytenoids

Figure 20-5. (A) Anterior and (B) posterior views of the laryngeal cartilages. 1 = epiglottis; 2 = lesser cornu of the hyoid bone; 3 = greater cornu of the hyoid bone; 4 = lateral thyrohyoid ligament; 5= body of hyoid bone; 6 = superior cornu of the thyroid cartilage; 7= thyroepiglottic ligament; 8= conus elasti-cus; 9 = cricothyroid ligament; 10 = thyroid cartilage; 11 = cricoid cartilage; 12= trachea; 13 = corniculate cartilage; 14 = arytenoid cartilage; 15 = posterior cricoarytenoid ligament; 16 = cricothyroid joint; 17= cricoarytenoid joint. (C) Lateral view of the laryngeal cartilages showing the location for a cricothy-roidotomy (CR) and a tracheotomy (TR). Note the anatomic layers that must be penetrated. CF= deep cervical fascia; PF= pretracheal fascia; S = skin; SF= superficial fascia. (D) Anatomic structures seen during inspection of the vocal folds with a laryngeal mirror. AEF = aryepiglottic fold; Epi= epiglottis; IN= interarytenoid notch; VOF= vocal fold; VSF= vestibular fold. (A, B, and D (right) adapted with permission from Rohen JW, Yokochi C, Lutjen-Drecoll E: Color Atlas of Anatomy, 4th ed. Baltimore, Williams & Wilkins, 1998, pp 154, 157; C (lower) adapted with permission from Moore KL: Clinically Oriented Anatomy 3rd ed. Baltimore, Williams & Wilkins, 1992, p 819; D (left) reprinted with permission from Pegington J: Clinical Anatomy in Action, vol. 2. The Head and Neck. Edinburgh, Churchill Livingstone, 1986.)

(true vocal cords). All intrinsic muscles of the larynx are innervated by the inferior laryngeal nerve of CN X (a continuation of the recurrent laryngeal nerve), except the cricothyroid muscle, which is innervated by the external branch of the superior laryngeal nerve of CN X. The intrinsic muscles of the larynx include:

1. The posterior cricoarytenoid muscle, which abducts the vocal folds and opens the airway during respiration. It is the only muscle that abducts the vocal folds.

2. The lateral cricoarytenoid muscle, which adducts the vocal folds

3. The arytenoid muscle, which adducts the vocal folds

4. The thyroarytenoid muscle, which relaxes the vocal folds

5. The vocalis muscle, which alters the vocal folds for speaking and singing

6. The transverse and oblique arytenoid muscles, which close the laryngeal aditus (sphincter function)

7. The cricothyroid muscle, which stretches and tenses the vocal folds B. Clinical considerations

1. Unilateral damage to the recurrent laryngeal nerve can result from dissection around the ligament of Berry or from ligation of the inferior thyroid artery during thyroidectomy. This damage causes hoarseness, inability to speak for long periods, and movement of the vocal fold on the affected side toward the midline.

2. Bilateral damage to the recurrent laryngeal nerve can result from dissection around the ligament of Berry or from ligation of the inferior thyroid artery during thyroidectomy. This damage causes acute breathlessness (dyspnea) because both vocal folds move toward the midline and close off the air passage.

3. Damage to the superior laryngeal nerve can result from ligation of the superior thyroid artery too far from the thyroid gland during thyroidectomy. This damage causes a weak voice with loss of projection and flaccid vocal cord on the affected side. This possibility can be avoided by ligating the superior thyroid artery where it enters the thyroid gland.

4. In cricothyroidotomy, a tube is inserted between the cricoid and thyroid cartilages for emergency airway management. The incision for this procedure passes through the following structures: skin > superficial fascia and platysma muscle (avoiding the anterior jugular veins) -> deep cervical fascia ► pretracheal fascia (avoiding the sternohyoid muscle) cricothyroid ligament (avoiding the cricothyroid muscle). The procedure may be complicated by the presence of a pyramidal lobe in the midline of the thyroid gland, which is seen in 75% of the U.S. population.

5. In tracheotomy, a tube is inserted between the second and third rings of the tracheal cartilage when long-term ventilator support is necessary, because insertion of a tube in this location reduces the incidence of vocal cord paralysis or subglottic stenosis. The incision for this procedure passes through the following structures: skin ► superficial fascia and platysma muscle (avoiding the anterior jugular veins) deep cervical fascia * pretracheal fascia > wall between cartilage rings. The following structures are at risk for injury: the inferior thyroid veins, which form a plexus anterior to the trachea; the thyroid ima artery, which is present in 10% of people and supplies the inferior border of the isthmus of the thyroid gland; and the thymus gland in infants. Tracheotomy can be complicated by massive hemorrhage 1-2 weeks after placement of the tube. The hemorrhage is caused by erosion of the brachiocephalic (innominate) artery.

IV. THYROID GLAND

A. General features

1. The arterial supply of the thyroid gland is from the external carotid artery through the superior thyroid artery, from the subclavian artery and thyrocervical trunk through the inferior thyroid artery, and sometimes from the arch of the aorta through the thyroid ima artery, which is present in approximately 10% of the U.S. population.

2. Venous drainage is to the superior, middle, and inferior thyroid veins, all of which empty into the internal jugular vein.

3. The right recurrent laryngeal nerve (which recurs around the subclavian artery) and left recurrent laryngeal nerve (which recurs around the arch of the aorta at the liga-mentum arteriosum) run in the tracheoesophageal groove along the posterior surface of the thyroid gland.

4. The ligament of Berry is the superior suspensory ligament of the thyroid gland. It is located adjacent to the cricoid cartilage on the posterior surface of the thyroid gland.

B. Clinical considerations

1. Complications of thyroidectomy include thyroid storm (hyperpyrexia and tachyarrhythmia), hypoparathyroidism (which may develop within 24 hours because of low serum calcium levels), and damage to the recurrent or superior laryngeal nerve.

2. Aberrant thyroid tissue may occur anywhere along the path of embryologic descent of the thyroid from the base of the tongue (foramen cecum), where this tissue is called a lingual cyst, to the superior mediastinum.

3. Thyroglossal duct cyst, located in the midline of the neck, is a cystic remnant of the descent of the thyroid during embryologic development.

V. PARATHYROID GLAND

A. General features. The parathyroid glands are yellow-brown masses, 2X3X5 mm in size and weighing approximately 40 g. Most people have four parathyroid glands, but five, six, or seven glands are possible. These glands rarely are embedded within the thyroid gland.

1. The superior parathyroid glands invariably are located on the posterior surface of the upper lobes of the thyroid, near the inferior thyroid artery. The inferior parathyroid glands are more variable in location but usually are found on the lateral surface of the lower thyroid lobes.

2. The arterial supply of the superior and inferior parathyroid glands is from the inferior thyroid artery.

B. Clinical considerations

1. Primary hyperparathyroidism results from autonomous secretion of parathyroid hormone (PTH) caused by glandular hyperplasia, adenoma or, rarely, carcinoma. The clinical sign is persistent hypercalcemia. In 90% of cases, surgical removal of the hyperfunctioning glands results in cure.

2. Injury to the parathyroid glands most commonly occurs during thyroidectomy as a result of disruption of the blood supply from the inferior thyroid artery.

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