Morphological Aspects of the Superficial Lymph Nodes of Myrmecophaga tridactyla

Abstract

Background: The giant anteater is a Xenarthra of the Myrmecophagidae family. It is classified in Brazil as vulnerable specie, however, in Rio de Janeiro and Rio Grande do Sul it is probably extinct. In an attempt to contribute to the preservation of the species, many injured animals are referred for treatment and rehabilitation, but the lack of information about morphology may hinder a more efficient clinical-surgical approach. The knowledge on the topography, dimensions and morphology of lymph nodes of a given species is essential for medical practice. The aim of this study was to identify and describe the general morphology of the superficial lymph nodes of Myrmecophaga tridactyla.

Materials, Methods & Results: Ten cadavers of adult Myrmecophaga tridactyla were used in this study. They were fixed and preserved with 10% formaldehyde solution and dissected throughout their length to locate their superficial lymph nodes. Lymph nodes of each center were removed for mesoscopic analysis. Measurements of width, length and thickness were obtained by a digital caliper. The superficial lymph nodes observed in the head were the mandibular and the intermandibular, while in the neck were identified superficial cervical and deep cervical lymph nodes. In the thoracic limbs, the axillary and the axillary accessory lymph nodes were present. In the pelvic limbs just one lymph node, the femoral, was observed, located in the thick subcutaneous fascia of the medial surface of the thigh. The main anatomical differences found in the lymph nodes of M. tridactyla are the absence of parotid, popliteal and subiliac lymph nodes and the presence of intermandibular lymph nodes and the developed femoral lymph nodes, which are unique in the pelvic limbs of this species. Moreover, some superficial lymph nodes were formed by several small lymph nodes, forming clusters, as observed in the proper and accessory axillary and femoral lymph nodes.

Discussion: The lymph nodes of the head, neck and forelimbs of the M. tridactyla followed the pattern observed in domestic animals and rats, while the morphological pattern of the lymph nodes of the head and the hindlimb differed from that described in domestic animals. Different from the dogs and ruminants where a range of superficial lymph nodes can be normally palpated, such as the mandibular; retropharyngeal; superficial cervical; subiliac; popliteal; mammary and superficial inguinal, only the femoral lymph nodes are palpable in M. tridactyla. The main reasons for this are the greater thickness of the skin and the absence of certain classic lymphocytes in the anteater. The peculiar anatomical features of the head and neck of M. tridactyla may have induced changes in the lymph centers of these regions when compared to the morphologic pattern of the terrestrial mammals in general. The lymph drainage of the neck, forelimbs and trunk wall was considered to be similar to that of dog, since there is equivalence of lymph nodes between these two species. The lymphatic afferents of the abdominal wall, gluteal region and hindlimbs are probably directed to the large femoral lymph nodes, which differs from domestic animals, whose lymph are mainly drained to the subiliac, ischiatic and popliteal lymph nodes. The anatomical differences related to the number, size and topography of the lymph nodes observed in M. tridactyla may be relevant in the medical procedures of this species.