APPLIED ANATOMY:Chapter8


Previous Chapter	Electronic Syllabi Home	Table of contents	Next chapter

Chapter 8. NECK AND THORAX

In horse & ox, the boundaries of the jugular furrow which houses the ext. jugular vein are formed by m. sternocephalicus below, and m. brachiocephalicus above. In pig, the site for cranial vena cava puncture is the depression just dorsolateral to manubrium of sternum (bounded by m. superficial pectoral and m. brachiocephalic.) Needle directed dorsocaudally in direction of opposite hip.

8.1 The Esophagus

Beginning dorsal to trachea, it inclines to the left of trachea as it travels down the neck, so that at the thoracic inlet it is between the trachea and the left first rib. Passing back through the thorax, it is forced upwards and towards midline by the bifurcation of the trachea and the arch of the aorta. Then, accompanied by dorsal & ventral esophageal trunks of vagus, it continues back between the lungs, inclining slightly towards the left with aorta above & the caudal vena cava below. Its termination is about the 11th thoracic vertebra in dog, 9th in ox, and 13th in horse.

From an anatomical point of view, locate potential blockage sites & identify structures encountered during surgical interference at these sites.

Note esophagus in relation to arch of aorta, pulmonary artery & ligamentum arteriosum. Compare with diagrams of abnormalities, the so-called 'vascular ring obstructions.'

Thoracic dissections: (live dog, ox, & horse)

On both sides, hinge all extrathoracic layers including forelimb & skin so that they can be raised to expose rib cage. Then remove intercostal muscles only as far back as costal attachment of diaphragm, thereby enabling you to assess the topography of thoracic contents. Then remove parts of ribs 2, 4, and 6 so that you can move parts of lung about. Do not remove lung until after you have done this.

Observe especially:-

Dog:- Basal (caudal) border of lung (approx. ventral point. of 6th rib to dorsal pt of 11th intercost. space). Diaphragm - approx. position of cranial curvature (6th rib or intercost. space) & costal attachment just within costal arch. Position of heart (note its relations to 4,5, & 6 c c. junctions). Chambers of heart (intracardial injections; right side behind 4 or 5 costochondral junction. Why might this be a good site?) Bifurcation of trachea, opposite 5th rib.

Thoracic oesophagus (follow out description given & see radiographs). Judge its accessibility in transthoracic surgery, usually in region of 4 - 6 ribs.

Dogs:- On left side of one dog , right side of another dog.., look at the inner aspect of the wall lined by parietal pleura, and note position of intercostal vessels & N. behind each rib. Familiarize yourself with the position of all relevant structures &, in particular, the thoracic oesophagus. Note its pleural investment, and take the opportunity of revising disposition of pleural sac as a whole. Note also dorsal and ventral oesophageal trunks of vagus.

Identify the left vagus N. in the cranial part of thorax; observe it passing over the arch of the aorta (at which point it gives off left recurrent N. which turns forward between the arch of the aorta, left bronchus, & left bronchial lymph node, as in the horse). Just after passing over arch of aorta, the left vagus N. divides into dorsal and ventral branches which unite with the corresponding branches of the right vagus to form the dorsal and ventral oesophageal trunks of vagus. Note position of vagus concerning transthoracic oesophagotomy.

Identify pulmonary artery, ligamentum arteriosum, and arch of aorta. diagrams of abnormalities in vascular obstructions. Coronary vessels are given off just above aortic valve, then the first large branch of aorta is the brachiocephalic a., followed by left subclavian a. The brachiocephalic a. divides into the two common carotid aa. & the right subclavian a.

8.2 Percussion & Auscultation of the Lungs

8.2.1Live Horse:-

8.2.1.1 Percussion of the Lungs:

The basal border of the percussion area runs dorsocaudad from the sixth rib at the level of the olecranon to the sixteenth space where it reaches a line through the ventral part of the tuber coxae. Here the basal border meets the dorsal border.

The resonance of the normal lung decreases gradually as one approaches the basal border. Caudal to the dorsal third of the right lung, there is an abrupt change to the flat liver sound. This is a good place to learn the difference. Ventral to the middle of the lung, there may be a resonant area caused by gas in the dorsal colon, but this resonance has a lower pitch than that of the lung.

8.2.1.2 Auscultation of the lungs

The normal lung sound is inspiratory. It is soft and hissing and in the resting horse it is only audible in the region close to the triceps. This normal inspiratory sound is said to be mainly a vesicular murmur with some stenotic sound transmitted from the larynx. If the horse is exercised the sound becomes louder and the lung may be outlined with the stethoscope. Listen to the trachea to hear the inspiratory and expiratory sound transmitted from the larynx. When this is heard distinctly in the thorax it is called a bronchial sound and is pathologic in the horse.

8.2.2 Live Ox

8.2.2.1 Percussion of the lungs:

The basal border of the percussion area is almost straight. It runs from the sixth costochondral junction to the eleventh intercostal space where it meets the dorsal border. This is a small area, compared to that of other animals.

Caudal to the dorsal third of the basal border of the left lung the resonance merges into the tympanitic sound of the upper part of the rumen, while in the right upper third, the resonance ends abruptly at the liver. In the middle thirds of the basal border on both sides, resonance ends abruptly because of the ingesta in the rumen and omasum.

8.2.2.2 Auscultation of the lungs:

The normal sound is much louder and harsher than in the horse. It is heard on inspiration and is loudest just caudal to the triceps. Outline the lung with the stethoscope. Listen to the trachea to hear the inspiratory and expiratory stenotic sound from the larynx. Some of this stenotic sound is said to be mixed with the vesicular murmur in the axillary and prescapular regions, but it is not heard distinctly over the rest of the thorax in the normal cow.

8.2.3 Live dog and cat

8.2.3.1Percussion of the lungs:

The basal border of the percussion area passes from the level of the olecranon at the sixth rib to the eleventh intercostal space. The resonance is more clearly heard, in comparison to the larger animals. The dog should stand during percussion.

8.2.3.2 Auscultation of the lungs:

Outline the area of the vesicular murmur. The bronchial sound is heard normally in the axillary region, but not over the rest of the lateral thoracic wall, except in the sleeping or somnolent dog.

8.3 Percussion and auscultation of the heart.

Live animals - It will save time if the fifth rib is located and marked. It is usually opposite the olecranon when the limb is vertical.

In percussion of the heart, two zones are described. (l) The area of absolute cardiac dullness corresponds to the area of contact of the pericardium with the thoracic wall. It gives a flat sound on light percussion. (2) The area of relative cardiac dullness is difficult to determine in animals. It is defined by somewhat stronger percussion and indicates the out-line of the heart which is covered by the thin margin of the lung. For practical purposes, the absolute dullness may be used to test for hypertrophy, displacement, and pericardial effusion. It should be kept in mind, however, that it is not the outline of the heart as it would be seen in a lateral radiograph.

The full craniocaudal extent in relation to the ribs is for reference only: Position of the Heart

Sp Cranial Extent Caudal Extent

Horse 2nd space 6th space

Ox 2nd space 5th space

Pig 2nd rib 5th rib

Dog 3rd rib 6th space

Cat 4th space 7th rib

The area of absolute dullness in the horse is a right triangle bounded by the triceps in front, the sternum below, and the lung. The object of percussion is to determine whether or not the heart is enlarged. On the left side of the normal horse, dullness extends about 7 cm. above the olecranon in the fourth space and about 3 cm. above the olecranon in the fifth space. On the right, the dullness extends about 3 cm. above the olecranon in the fourth space only.

In the ox, the normal area of absolute dullness is too far cranial for percussion. The lower limits of lung resonance in the fourth and fifth spaces should be carefully explored. Traumatic pericarditis may produce absolute dullness in these spaces, extending above a horizontal line through the shoulder joint.

Small dogs are most easily percussed by holding them in the sitting-up position and working on the ventral surface of the thorax. On the left side the cardiac dullness extends out to the costochondral junctions in spaces four and five, not so far in six. On the right side the dullness extends only 1-2 cm. from the sternum in spaces four and five.

In auscultation, the first heart sound heard in each cycle is caused by the closing of the right and left atrioventricular valves. The second sound is caused by the closing of the aortic and pulmonary valves.

The puncta maxima (point of maximum audibility) established for the valves do not necessarily correspond with the anatomic positions of the valves. The puncta maxima were determined by comparison of clinical and autopsy findings in valvular disease. In some cases the sound is conducted to a point on the thoracic wall which is not in the plane of the valve.

The locations of the puncta maxima may be summarized in general terms for all species as follows:

Left AV

Low in the left fifth intercostal space (fourth in the ox). This is at the level of the olecranon or the costochondral junction in the dog.

Aortic Valve

High in the left fourth space, just below a horizontal line passing through the shoulder joint.

Pulmonary

Low in the left third space.

Right AV.

Low in the right third or fourth space.

An efficient procedure is to begin with the left AV valve, where the first sound is loudest; then gradually move the stethoscope cranially until the second sound reaches maximum intensity over the pulmonary valve. Return to the left AV valve and gradually move the stethoscope dorsally in the fourth space until the second sound reaches maximum intensity over the aortic valve.

8.4 LYMPH NODES (OX)

8.4.1 Superficial cervical (prescapular)

4" or 5" above level of shoulder joint (covered by mm brachiocephalicus and omotransversarius). Palpable in live animal.

8.4.2 Caudal cervical

near thoracic inlet, close to brachial vessels as they turn round first rib.

8.4.3 Costocervical

against trachea (right side) and oesophagus _(left side) at thoracic inlet, within or just in front of first rib.

8.4.4 Bronchial and caudal mediastinal are incised routinely in postmortem inspections of cattle. The other groups are incised in final inspection.

8.4.5 Thoracic lymph nodes

8.4.5.1 Bronchial:

The left bronchial node is located by drawing the left apical lobe of the lung back and incising back to the left bronchus: the node can be seen lying between the arch of aorta, pulmonary artery, and bronchus. On the right side, the apical bronchial node is the one commonly examined: it lies on the right side of the trachea just cranial to the special bronchus of the right apical lobe.

8.4.5.2 Caudal mediastinal:- this group lies between the aorta and the esophagus, the most cranial one at the aortic arch, the most caudal at the diaphragm. One is normally large, it can be clearly seen. Abnormal enlargement may cause constriction of oesophagus.

8.4.5.3 Cranial mediastinal:- these are in the fat around trachea, oesophagus, and large vessels cranial to the heart.

8.4.5.4 Sternal mediastinal:- the most cranial sternal node is large and is not covered by the muscles (transversus thoracis); the others are under the muscle and lie on the course of the internal thoracic vessels.

SPECIMENS OF OX PELVIS - note the position of the following groups of lymph nodes:-

8.4.5.5 Iliac:- They are related to the terminal branches of the aorta; several nodes 1/2"-2" long. They receive lymph from immediate vicinity and from rectum and urogenital organs, also from other nodes such as prefemoral and deep inguinal.

8.4.5.6 Deep inguinal:- Usually one large node 2" - 3", on either side, situated at the divergence of ext. iliac artery from circumflex iliac a.

8.4.5.7 Ischiatic - may be in the lesser sciatic foramen or dorsal to it, lateral to sacrosciatic ligament. (In meat inspection, reached from inside split carcass by incising sacrosciatic ligament.)

8.4.5.8 Subiliac:- (prefemoral) - high up in the fold of the flank. Palpable in live animal.

8.5 SITES OF ATLANTAL & SUPRASPINOUS BURSITIS

8.5.1 HORSE.

8.5.1.1 The ligamentum nuchae is a powerful elastic apparatus, the principal function of which is to assist the extensor muscles of the head and neck. It extends from the occipital bone to the withers, where it is directly continuous with the supraspinous ligament. It consists of two parts - funicular and lamellar; it is the former which is involved in above conditions.

8.5.1.2 The funicular part arises from the external occipital protuberance, and is inserted into the summits of the vertebral spines at the withers (2nd to 4th thoracic spines). At the occipital attachment, it is strong but narrow; near the withers it broadens and then behind the higher spines it narrows as it is continued by the supraspinous ligament.

8.5.1.3 The atlantal bursa lies between the ligament and the dorsal arch of the atlas. There may also be an axial bursa between it and the spine of the axis. Access to the atlantal bursa (for poll evil) is through skin and fascia to the lig. nuchae, or between it and the muscles alongside (dorsal straight muscles of head).

The supraspinous bursa is most commonly over the 2nd thoracic spine, but may extend back to 4th, or there may be small separate bursae over the spines. The dorsoscapular ligament is a layer of strong fascia attaching to the 3rd, 4th, and 5th thoracic spines (fusing there with the supraspinous lig.) and giving attachment to mm rhomoboideus, splenius, and complexus; as it is traced ventrally, it divides into lamellae some of which reach the scapula).

Access to the supraspinous bursa (for fistulous withers) is through the skin and m. trapezius, then down to lig. nuchae or between it and m. rhomoboideus, retracting the rhomboid down to level of dorso-scapular ligament.

The lamellar part of the lig. nuchae consists of two laminae, each lamina formed of digitations which arise from 2nd and 3rd thoracic spines and from the funicular part, and are directed downward and forward to end on the spines of the cervical vertebrae except the first and the last.

8.6 CLINICAL CONSIDERATIONS:

The following are some clinical considerations relevant to:

- Oesophageal obstruction

- Oesophagotomy (cervical)

- Oesophagotomy

- Tracheotomy

- Vascular ring obstruction (Anomalies of aortic arch orsubclavian arteries)

- Patent ductus arteriosus

- Diaphragmatic hernia

- Percussion and auscultation of lungs

- Percussion and auscultation of heart

- Venipuncture

- Intracardial injections

- Thoracentesis

- Thoracotomy

- Lower oesophageal achalasia

- Lymph nodes, ox

- Atlantal and supraspinous bursitis, horse

Equine

Bovine

Canine

Subdivisions of mediastinum