Important Accessible lymph nodes for Clinical examination in farm animals.

Important Accessible lymph nodes for Clinical examination in farm animals.

P SENTHAMIL SELVAN,  K RAJALAKSHMI and YAMINI S

Department of Veterinary Anatomy and Histology, RIVER, Puducherry

Puducherry-605 009. Email- drsenvet@gmail.com,

INTRODUCTION:

The immune system of animals provides immunity (both cell mediated and humoral immunity) against invading pathogens and maintains the health of the animal in normal conditions. Lymph nodes act as natural barriers against the invasion of pathogens via lymph. These pathogens when are not effectively checked, destroyed and removed by the immune system may lead to a disease. Clinical examination of animals helps to identify abnormalities and the associated risk factors in a disease condition. In clinical practice examination of lymph nodes is an important procedure that help detect any local or generalized disease in an animal. It is imperative for a veterinarian to identify the location of these palpable lymph nodes and their supply to determine the severity and extent of a disease condition in farm animals.

 FUNCTIONAL ANATOMY OF LYMPH NODES:

Lymph nodes are the structural and functional units of the lymphatic system.  They occur in specific regions in an animal body known as the lympho centers. These lymphocenters are fixed and they drain specific regions of the body.  Therefore, these Lymph nodes serve as indicators of any local or systemic disease process and are easily accessible for examination in animals. The lymph nodes are encapsulated bean shaped organs. Their size varies from few millimeters to several centimeters.  It is surrounded by an outermost capsule formed of collagen fibers.  Connective tissue extensions from the capsule namely the trabaculae enters into the parenchyma.  The parenchyma of the lymph node posses an outer cortex and an inner medulla. The cortical zone is occupied by primary and secondary lymphoid nodules (follicles). Primary follicles lack a germinal center and is formed of tightly packed uniform cells especially small lymphocytes. The secondary follicle shows a germinal center with larger cells that can actively proliferate. Both primary nodules and the germinal centers of the secondary nodules are concentrated with B lymphocytes. The internodular region and the deeper part of the cortex is referred as the paracortex. Paracortex is occupied by T lymphocytes. Mature B cells and differentiated B cells/ plasma cells are seen surrounding the germinal centers. The medullary region is formed of cords of lymphocytes with sinuses and lymph capillaries between them. The cells that helps to present antigen to the T lymphocytes and B lymphocytes inside the lymph node are the dendritic cells. They are the antigen presenting cells that can trap antigen entering through afferent vessels.

The lymph from the adjacent areas are drained and presented to the lymph node by the afferent vessels that enters via the capsule. The lymph flows unidirectional towards the hilus through the follicles that act as the filters. The filtered lymph leaves the lymph node through efferent vessels at the hilus. The follicles, with antigenic stimulation can actively produce lymphocytes and plasma cells and promotes cell mediated immunity, humoral immunity by secreting antibodies and makes an immunologic memory.

In porcines, the lymphatic nodules inside the lymph nodes are more centrally located while the medullary cords and cell aggregates are peripheral. But the flow of lymph inside these lymph nodes follows the same pattern.

ACCESSIBLE AND SUPERFICIAL LYMPH NODES:

Lymph nodes vary in size within an individual animal. They are firm and smooth. Lobulation may be felt in larger lymph nodes. Lymph nodes are loosely attached and are mobile. When located superficial, the skin over the lymph node is free and loose above these nodes. The shape varies from spherical, oval to elliptical. The colour of the lymph node is usually grayish brown and may have light and dark markings. Their appearance in general depends on the age, breed, species and its location within an animal. Though there are numerous lymph nodes that are distributed in the body few of these lymph nodes are easily accessible and are recommended for their examination in clinical practice, and at antemortem and postmortem procedures. Any gross enlargement of these lymph nodes may be visual detected. Changes in their shape, size, consistency, position, sensitivity to touch (pain response) can be assessed by palpating the respective lymph node. If the lymph nodes are paired both are to be palpated and compared.

The details on the location, afferent and efferent supply to these palpable lymph nodes of clinical importance are as follows.

1.Parotid LN: It is located ventral to the temporo mandibular joint and lies on the caudal part of the masseter muscle. It is partly covered by the parotid salivary gland. Afferent vessels are from the muzzle, lips, gums, anterior part of turbinate, nasal septum, parotid salivary gland, lacrimal gland, external ear, most of the head muscles and greater part of the head skin. The efferent vessels supply the atlantal lymph node.

2. Mandibular LN: It is situated between the sternocephalicus muscle and the ventral part of the mandibular salivary gland. It is related dorsally to the external maxillary vein. Afferent vessels are from the muzzle, lips, cheek, hard palate, anterior part of the turbinates, nasal septum, gums, sublingual and parotid glands, tip of the tongue, some head muscles and part of the skin of the face. Efferent vessels supply atlantal lymph node.  They are usually 2 in sheep. The most common sites at which tuberculosis lesions are likely to occur is the mandibular lymph node.

3.Lateral retropharyngeal LN: It is present medial to the stylo- hyoid, between the pharynx above and the ventral straight muscles of the neck below. Afferent vessels are from the tongue, hard palate, soft palate, part of gums, floor of mouth, pharynx, sublingual and mandibular salivary glands, posterior part of the nasal cavity, larynx, maxillary and palatine sinuses. The efferent vessels join to form the tracheal lymph duct.

4. Prescapular LN: It is situated at the cranial border of the supraspinatus muscle. It is long and elongated, seen above the shoulder joint. Afferents  are from the skin of neck, shoulder, part of ventrolateral aspect of thorax and forelimb, muscles of the pectoral girdle, scapular muscles, muscles and joints of the fore arm and digit. The efferent opens in to the respective tracheal duct.

5.Prefemoral LN:  It is present five or six inches above the patella close to the tensor fascia lata muscle. It is flattened and elliptical and is above the aponeurosis of the obliquus abdominis externus muscle. Its afferent vessels are from the skin of posterior thorax, abdomen, pelvis, thigh, leg and prepuce. Efferent vessels end mostly in the deep inguinal and less often in the iliac lymph nodes. It is kidney shaped in sheep

6.Superficial inguinal:

1. Mammary LN in females:They are present above the caudal border of the base of the udder. They are usually two in number on either side. The afferent vessels are from the udder, genital organs, part of the skin of thigh and leg. Efferent vessels open in to the deep inguinal glands.
2. Scrotal LN in males:In bull they are present below the prepubic tendon at the neck of the scrotum behind the spermatic cord. Afferent vessels are from the testicles, skin of adjacent regions, medial aspect of the thigh and leg. The efferent vessels open in the deep inguinal lymph node.

7.Popliteal LN: Deep Popliteal LN is located in the fat on the gastrocnemius muscle between gluteobiceps and semitendinosus muscle. Afferent vessels are from the posterior and lateral part of the leg, distal part of the hindlimb, semitendinosus and biceps femoris muscle. Efferent vessels chiefly ends in deep inguinal lymph node.

8. Axillary LN:They are found on the medial aspect of the shoulder where the brachial artery and brachial plexus enter the forelimb in the region of the axilla. They can be palpated and located in calves that are lean but not in adulat animals. Afferent supply is from muscles and fascia of the shoulder, arm and forearm. Efferent vessels open in posterior cervical lymph nodes.
9. Internal Iliac LN:These are palpable on rectal examination just anterior to the wing of the ilium on either side at the termination of the abdominal aorta. Their afferent vessels are from sublumbar muscles, pelvis, tail, thigh, urogenital organs, and from external iliac, sacral, ischiatic, deep inguinal prefemoral and coxal lymph nodes. Efferent vessels opens into the lumbar trunk.

COMMON PATHOLOGIES OF LYMPH NODES:

Clinical Examination of lymph nodes require special attention in determining the size, shape, and consistency of nodes. The gross morphological changes on palpation may vary from  smooth and relatively soft, to  rubbery and hard consistency, with changes in its shape and size due to various pathologies in lymph nodes. The common pathologies include

1. Atrophy:Lymph node reduce in size. It is associated with some viral infections, ionizing radiation, old age, starvation, chronic wasting diseases, excessive hormone and corticosterone
2. Hypoplasia:The cell density and therefore size of lymph nodes reduces and is due to infective and toxic agents and hormones.
3. Necrosis:Necrotic areas in lymph nodes develop when infective agents grow in those areas in infectious diseases.
4. Hyperplasia:In subacute and chronic irritation. Affected nodes are seen enlarged, firm without fibrosis and calcification.
5. Pigmentation:(Exogenous) due to pigments ingested through feeds. (Endogenous) brownish lymph nodes due to hemosiderin accumulation indicates hemorrhagic lesions in its draining areas.
6. Emphysema:Accumulation of air in lymph nodes. The nodes are seen enlarged, soft and puffy.
7. Hemorrhages:In severe infections, local trauma and passive venous congestion.
8. Inflammation:Lymphadenitis, is caused by long term inflammation caused by     bacterial, viral or fungal infections. When one or few closed lymph nodes are    involved it is called localized lymphadenitis. In a spreading infection two or more    groups of  lymph nodes will be involved and cause Genaralised lymphadenitis.Based on the nature of exudates lymphadenitis may be Acute, serous, hemorrhagic,        Suppurative and Chronic type.

Neoplasms:Lymphoma is a common malignancy in animals. The affected lymph nodes may be matted or seen fixed to the underlying structures.

REFERENCE:

1. Sisson, S., and Grossman, J. D., (1962). The anatomy of the domestic animals, 4^thEdn,Asia Publishing House.
2. Jackson, P.G.G., and Cockcroft, P.D., (2002) Clinical examination of farm animals. Blackwell Publishing Company, UK.
3. Bhardwaj, R.L., Rajput, R., and Roy . (2002). Applied Anatomy of domestic animals. Kalyani publishers. New Delhi.
4. Scott, P., (2011). Lymphatic and other tumors in cattle. National animal disease information service. https://www.nadis.org.uk/disease-a-z/cattle/lymphatic-and-other-tumours-in-cattle
5. Herenda, D., Chambers, P.G., Ettriqui, A., Seneviratna, P., da silva, D.J.P., (2000). Specific disease of cattle, Chapter-3 in Manual on meat inspection for developing countries. FAO, UN,
6. Luckins AG, Gray AR. Trypanosomes in the lymph nodes of cattle and sheep infected with Trypanosoma congolense. Res Vet Sci. 1979 Jul;27(1):129-31. PMID: 504804.
7. Mobini, S., Wol, C., and Pugh, D.G. (2002). Flock health, Chapter 17 in Sheep and Goat Medicine. W.B. Saunders, pp 421-434.
8. Sastry, Ganti A., and Rao, Rama. P. (2001). Veterinary Pathology. 7 Edition, CBS Publishers and Distributers, New Delhi.

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