Comparative evaluation of the cadaveric, radiographic and computed tomographic anatomy of the heads of green iguana (Iguana iguana), common tegu (Tupinambis merianae) and bearded dragon (Pogona vitticeps)

Abstract

Background: Radiology and computed tomography are the most commonly available diagnostic tools for the diagnosis of pathologies affecting the head and skull in veterinary practice. Nevertheless, accurate interpretation of radiographic and CT studies requires a thorough knowledge of the gross and the cross-sectional anatomy. Despite the increasing success of reptiles as pets, only a few reports over their normal imaging features are currently available. The aim of this study is to describe the normal cadaveric, radiographic and computed tomographic features of the heads of the green iguana, tegu and bearded dragon.

Results: 6 adult green iguanas, 4 tegus, 3 bearded dragons, and, the adult cadavers of: 4 green iguana, 4 tegu, 4 bearded dragon were included in the study. 2 cadavers were dissected following a stratigraphic approach and 2 cadavers were cross-sectioned for each species. These latter specimens were stored in a freezer (-20°C) until completely frozen. Transversal sections at 5 mm intervals were obtained by means of an electric band-saw. Each section was cleaned and photographed on both sides. Radiographs of the head of each subject were obtained. Pre- and post- contrast computed tomographic studies of the head were performed on all the live animals. CT images were displayed in both bone and soft tissue windows. Individual anatomic structures were first recognised and labelled on the anatomic images and then matched on radiographs and CT images. Radiographic and CT images of the skull provided good detail of the bony structures in all species. In CT contrast medium injection enabled good detail of the soft tissues to be obtained in the iguana whereas only the eye was clearly distinguishable from the remaining soft tissues in both the tegu and the bearded dragon.

Conclusions: The results provide an atlas of the normal anatomical and in vivo radiographic and computed tomographic features of the heads of lizards, and this may be useful in interpreting any imaging modality involving these species.

Figure 1

Normal radiographic anatomy of the head of the green iguana in VD projection. A. Ventral view in a superficial plane of stratigraphic dissection (only skin was removed) of the head of an iguana. B. Ventral view of stratigraphic dissection after removal of Musculus constrictor colli and Musculus intermandibularis (lower part of the image) and a deeper plane of dissection (upper part of the image) of the head of an iguana (deeper plane of dissection is labelled with * on the image). C. VD radiographic projection of the head of an iguana. Ro is rostral, L is left.1. Premaxillary bone; 2. Dentary bone; 3. Musculus intermandibularis; 4. Musculus geniohyoideus; 5. Musculus hyoglossus; 6. Musculus pterygoideus typicus; 7. Ceratobranchial 1 process of the hyobranchial skeleton; 8. Vomer bone; 9. Musculus genioglossus; 10. Tendinous band; 11. Ceratohyal process of the hyobranchial skeleton; 12. Ceratobranchial 2 process of the hyobranchial skeleton; 13. Musculus omohyoideus; 14. Palatine bone; 15. Ectopterygoid bone; 16. Pterygoid bone; 17. Jugal bone; 18. Postorbital bone; 19. Articular bone + quadrate bone; 20. Parietal bone; 21. Basioccipital bone; 22. Paraoccipital process of otooccipital bone; 23. Adductor fossa; 24. Epipterygoid bone; 25; Interpterygoid vacuiti; 26. Maxillary bone.

Figure 2

Normal radiographic anatomy of the head of the green iguana in LL projection.A. LL photographic image in a superficial plane of the stratigraphic dissection of the head of an iguana (only skin was removed). B. LL photographic image in a deep plane of the stratigraphic dissection of the head of an iguana. C. LL radiographic projection of the head of an iguana. Ro is rostral, Do is dorsal. 1. Premaxillary bone; 2. Nasal bone; 3. Maxillary bone; 4. Prefrontal bone; 5.Frontal bone; 6. Eye; 7. Jugal bone; 8. Postorbital bone; 9. Musculus adductor mandibulae externus medialis; 10. Musculus adductor mandibulae externus superficialis; 11. Ear; 12. Musculus depressor mandibulae; 13. Musculus episternocleidomastois; 14. Musculus pterygoideus typicus; 15. Musculus intermandibularis posterior; 16. Quadrato-maxillary ligament; 17. Dentary bone; 18. Squamosal bone 19. Musculus trapezius + Musculus clavicle dorsalis; 20. Musculus episternocleidomastoid; 21. Articular bone; 22. Angular bone + Surangular bone; 23. Adductor chamber; 24; Coronoid bone; 25. Ceratobranchial process of hyobranchial skeleton; 26. Hyobranchial skeleton; 27. Quadrate bone; 28. Oesophagus; 29. Pila metoptica; 30. Epipterygoid bone; 31. Nasal glands; 32. Scleral ossicles; 33. Parietal bone; 34. Vomer bone; 35; Palatine bone; 36; Pterygoid bone; 37. Trachea.

Figure 3

Normal computed tomographic anatomy of the head of the green iguana.A. Photograph of the head of an iguana; lines (1–3) indicate the approximate levels of matched cross-sections and CT images. B- J: Matched images of cross-sectional gross anatomy ( B- E- H), CT image displayed in bone window (WW: +2000; WL: +500) ( C- F- I) and CT image displayed in soft tissue window (WW: +400; WL: +40)( D- G- J) corresponding to: line 1 ( B- C- D), line 2 ( E- F- G) and line 3 ( H- I- J) as depicted in Figure 3A. R is right and Ve is ventral. B- C- D: 1. Nasal bone; 2. Prefrontal bone; 3. Stammteil; 4. Nasal septum; 5. Nasal glands; 6. Subconchal recess; 7.Vomer bone; 8. Choanal tube; 9. Maxillary bone; 10. Cavum oris; 11. Dentary bone; 12. Meckelian fossa; 13. Entoglossal process of the basihyal bone; 14. Musculus geniohyoideus + Musculus hyoglossus + Musculus intermandibularis; 15. Tongue. E- F- G: 1. Frontal bone; 2. Brain; 3. Harderian gland; 4. Choroid plexus; 5. Interorbital septum; 6. Vitreous humor; 7. Lens; 8. Sinus orbitalis; 9. Maxillary bone; 10. Palatine glands; 11. Palatine bone; 12. Dentary bone; 13: Entoglossal process of the basihyal bone; 14. Tongue; 15. Musculus geniohyoideus + Musculus hyoglossus + Musculus intermandibularis; 16. Cavum oris; 17. Scleral ossicles. H- I- J: 1. Parietal bone; 2. Brain; 3. Vena cerebralis media; 4. Sphenoid bone; 5. Angular bone + Surangular bone; 6. Hyobranchial skeleton; 7. Musculus intermandibularis + Musculus genioyhoideus + Musculus hyoglossus + Musculus pterygoideus + Musculus omohyoideus + Musculus stermohyoideus + Musculus ceratohyoideus; 8. Trachea; 9. Oesophagus; 10. Musculus adductor mandibulae externus medialis; 11. Musculus adductor mandibulae externus superficialis; 12. Adductor fossa.

Figure 4

Normal radiographic anatomy of the head of the common tegu in VD projection.A. Ventral view in a superficial plane of stratigraphic dissection (only skin was removed) of the head of a tegu. B. Ventral view of stratigraphic dissection after removal of Musculus constritor colli and Musculus intermandibularis (lower part of the image) and a deeper plane of dissection (upper part of the image) of the head of a tegu (deeper plane of dissection is labelled with * on the image). C. VD radiographic projection of the head of a tegu. Ro is rostral, L is left.1. Premaxillary bone; 2. Infralabial glands; 3. Dentary bone; 4. Musculus intermandibularis; 5. Musculus adductor mandibulae externus superficialis; 6. Musculus hyoglossus; 7. Musculus pterygoideus; 8. Basihyal bone; 9. Musculus constrictor colli; 10. Tongue; 11. Oesophagus; 12. Palatine bone; 13. Pterygoid bone; 14. Entoglossal process of hyobranchial skeleton; 15. Ceratobranchial process of hyobranchial skeleton; 16. Musculus omohyoideus; 17. Musculus sternohyoideus; 18. Trachea; 19. Maxillary bone; 20. Prefrontal bone; 21. Jugal bone; 22. Squamosal bone; 23. Ectopterygoid bone; 24. Postorbital bone; 25. Frontal bone; 26. Surangular bone; 27. Adductor fossa; 28. Angular bone; 29. Articular bone; 30. Basioccipital + Supraoccipital bones; 31. Paraoccipital process of otooccipital bone; 32. Hyobranchial skeleton; 33. Quadrate bone; 34. Parietal bone; 35. Epipterygoid bone; 36. Postfrontal bone; 37. Parieto-frontal suture; 38. Interpterygoid vacuity; 39. Vomer bone.

Figure 5

Normal radiographic anatomy of the head of the common tegu in LL projection.A. LL photographic image in a superficial plane of the stratigraphic dissection of the head of a tegu (only skin was removed). B. LL photographic image in a deep plane of the stratigraphic dissection of the head of a tegu C. LL radiographic projection of the head of a tegu. Ro is rostral, Do is dorsal. 1. Premaxillary bone; 2. Nasal bone; 3. Maxillary bone; 4. Frontal bone; 5. Eye; 6. Postorbital bone; 7. Musculus adductor mandibulae externus medialis; 8. Squamosal bone; 9. Musculus depressor mandibulae; 10. Musculus constrictor colli; 11. Supralabial glands; 12. Infralabial glands; 13. Jugal bone; 14. Musculus adductor mandibulae externus superficialis; 15. Ear; 16. Musculus obliquus capitis magnus; 17. Musculus spinalis; 18. Dentary bone; 19. Trachea; 20. Hyobranchial skeleton; 21. Septomaxilla; 22. Scleral ossicles; 23. Palatine bone; 24. Pila metoptica; 25. Parietal bone; 26. Epipterygoid bone; 27. Occipital bone; 28. Quadrate bone; 29. Rostrum parasphenoid; 30. Articular bone; 31. Angular + Surangular bone; 32. Pterygoid bone; 33. Coronoid bone; 34. Vomer bone.

Figure 6

Normal computed tomographic anatomy of the head of the common tegu.A. Photograph of the head of a tegu; lines (1–3) indicate the approximate levels of matched cross-sections and CT images. B- J: Matched images of cross-sectional gross anatomy ( B- E- H), CT image displayed in bone window (WW: +2000; WL: +500)( C- F- I) and CT image displayed in soft tissue window (WW: +400; WL: +40) ( D- G- J) corresponding to: line 1 ( B- C- D), line 2 ( E- F- G) and line 3 ( H- I- J) as depicted in Figure 6A. R is right and Ve is ventral. B-C-D: 1. Nasal bone; 2. Nasal glands 3. Prefrontal bone; 4. Nasal conchae; 5. Septomaxilla; 6. Maxillary bone; 7. Dentary bone; 8. Meckelian canal 9. Infralabial glands; 10. Tongue; 11. Trachea. E- F- G: 1. Frontal bone; 2. Scleral ossicles; 3. Palatine bone; 4. Palatine gland; 5. Maxillary bone; 6. Dentary bone; 7. Meckelian canal; 8. Eye; 9. Lens; 10. Sinus orbitalis; 11. Harderian gland; 12. Tongue; 13. Musculus intermandibularis + Musculus geniohyoideus + Musculus genioglossus + Musculus hyoglossus; 14. Infralabial glands. H- I- J: 1. Parietal bone; 2. Squamosal bone; 3. Sphenoid bone; 4. Pterygoid bone; 5. Angular bone + Surangular bone; 6. Adductor fossa; 7. Brain; 8. Musculus longus colli; 9. Musculus adductor mandibulae externus profundus; 10. Musculus abductor mandibularis externus medialis; 11. Musculus intermandibularis posterior; 12. Musculus pterygoideus typicus + Musculus pterygoideus atypicus; 13. Musculus intermandibularis + Musculus geniohyoideus + Musculus pterygoideus typicus + Musculus hyoglossus; 14. Trachea.

Figure 7

Normal radiographic anatomy of the head of the bearded dragon in VD projection.A. Ventral view in a superficial plane of stratigraphic dissection (only skin was removed) of the head of a bearded dragon. B. Ventral view of stratigraphic dissection after removal of Musculus constrictor colli and Musculus intermandibularis (lower part of the image) and a deeper plane of dissection (upper part of the image) of the head of a bearded dragon (deeper plane of dissection is labelled with * on the image). C. VD radiographic projection of the head of a bearded dragon. Ro is rostral, L is left.1. Musculus intermandibularis; 2. Dentary bone; 3. Supralabial gland; 4. Musculus adductor mandibulae externus supeficialis; 5. Ceratobranchial 1 process of hyobranchial skeleton; 6. Fat body; 7. Trachea; 8. Fat body; 9. Musculus constrictor colli; 10. Ceratohyal process of hyobranchial skeleton; 11. Basihyal bone; 12. Musculus pterygoideus typicus; 13. Maxillary bone; 14. Oesophagus; 15. Premaxillary bone; 16. Prefrontal bone; 17. Palatine bone; 18. Frontal bone; 19. Jugal bone; 20. Epipterygoid bone; 21; Squamosal bone; 22. Angular bone + Surangular bone; 23. Quadrate bone; 24. Articular bone; 25. Paraoccipital process of otooccipital bone; 26. Pterygoid bone; 27. Coronoid bone; 28. Ectopterygoid bone; 30. Interpterygoid vacuiti; 31. Vomer bone.

Figure 8

Normal radiographic anatomy of the head of the bearded dragon in LL projection.A. LL photographic image in a superficial plane of the stratigraphic dissection of the head of a bearded dragon (only skin was removed). B. LL photographic image in a deep plane of the stratigraphic dissection of the head of a bearded dragon. C. LL radiographic projection of the head of a bearded dragon. Ro is rostral, Do is dorsal. 1. Premaxillary bone; 2. Nostril; 3. Prefrontal bone; 4. Eye; 5. Maxillary bone; 6. Postorbital bone; 7. Jugal bone; 8. Musculus adductor mandibulae externus superficialis; 9. Ear; 10. Musculus adductor mandibulae externus medialis; 11. Musculus pterygoideus typicus; 12. Musculus depressor mandibulae; 13. Fat body; 14. Ceratobranchial process of hyobranchial skeleton; 15. Musculus sphincter colli; 16. Quadrato maxillary ligament; 17. Infralabial glands; 18. Supralabial gland; 19. Dentary bone; 20. Tongue; 21. Musculus trapezius + Musculus clavicle dorsalis; 22. Musculus episternocleidomastoid; 23. Trachea; 24. Articular bone; 25. Angular bone + Surangular bone; 26. Frontal bone; 27. Parietal bone; 28. Squamosal bone; 29. Paraoccipital process of otooccipital bone; 30. Quadrate bone; 31. Epipterygoid bone; 32. Coronoid bone; 33. Ectopterygoid bone; 34. Pterygoid bone; 35. Scleral ossicles; 36. Palatine bone; 37. Vomer bone.

Figure 9

Normal computed tomographic anatomy of the head of the bearded dragon.A. Photograph of the head of a bearded dragon; lines (1–3) indicate the approximate levels of matched cross-sections and CT images. B- J: Matched images of cross-sectional gross anatomy ( B- E- H), CT image displayed in bone window (WW: +2000; WL: +500)(C-F-I) and CT image displayed in soft tissue window (WW: +400; WL: +40) ( D- G- J) corresponding to: line 1 ( B- C- D), line 2 ( E- F- G) and line 3 ( H- I- J) as depicted in Figure 9A. R is right and Ve is ventral. B- C- D: 1. Nasal bone; 2. Nasal septum; 3. Choanae; 4. Vomer bone; 5. Tongue; 6. Musculus intermandibularis + Musculus geniohyoideus + Musculus genioglossus; 7. Nasal glands; 8. Choanal tube; 9. Maxillary bone; 10. Dentary bone; 11. Meckelian canal. E- F- G: 1. Frontal bone; 2. Eye; 3. Scleral ossicles; 4. Harderian gland; 5. Sinus orbitalis; 6. Palatine gland; 7. Pterygoid bone; 8. Cavum oris; 9. Sublingual gland; 10. Brain; 11. Choroid plexus; 12; Postorbital bone + Jugal bone; 13. Musculus adductor mandibulae externus superficialis; 14. Dentary bone; 15. Tongue; 16. Infralabial glands; 17. Meckelian canal; 18. Entoglossal process of the hyobranchial skeleton; 19. Musculus intermandibularis + Musculus geniohyoideus + Musculus hyoglossus + Musculus pterygoideus typicus. H- I- J: 1. Musculus adductor mandibulae externus medialis; 2. Brain; 3. Quadrate bone; 4. Musculus longus colli; 5. Trachea; 6. Musculus pterygoideus typicus; 7. Postparietal process of otooccipital bone; 8. Orbitosphenoid bone; 9. Musculus adductor mandibularis externus superficialis; 10. Angular bone + Surangular bone; 11. Adductor fossa; 12. Musculus intermandibularis + Musculus geniohyoideus + Musculus ceratohyoideus + Musculus hyoglossus.