ANATOMIC ATLAS FOR COMPUTED TOMOGRAPHY IN THE MESATICEPHALIC DOG: HEAD AND NECK THOMAS F. GEORGE11, DVM, MS
JAMESE. SMALLWOOD, DVM, MS
AND
The purpose of this study was to produce a comprehensive anatomic atlas of CT anatomy of the dog for use by veterinary radiologists, clinicians, and surgeons. Whole-body CT images of two mature beagle dogs were made with the dogs supported in sternal recumbency and using a slice thickness of 13 mm. The head was scanned using high-resolution imaging with a slice thickness of 8 mm. At the end of the CT session, each dog was euthanized, and while carefully maintaining the same position, the body was placed in a walk-in freezer until completely frozen. The body was then sectioned at 13-mm (head at 8-mm) intervals, with the cuts matched as closely as possible to the CT slices. The frozen sections were cleaned, photographed, and radiographed using xeroradiography. Each CT image was studied and compared with its corresponding xeroradiograph and anatomic section to assist in the accurate identification of specific structures. Intact, sagittally sectioned, and disarticulated dog skulls were used as reference models. Clinically relevant anatomic structures were identified and labeled in the three corresponding photographs (CT image, xeroradiograph, and anatomic section). In this paper, the CT anatomy of the head and neck of the mesaticephalic dog is presented. Veterinary Radiology & Ultrasound, Vol. 33, No. 4 , 1992, p p 217-240 Key Words: computed tomography, dog, anatomy, head, neck
Introduction
C
(CT) currently enjoys a prominent role in the diagnosis and evaluation of many human diseases, and CT scanners are now in place at many veterinary schools in the United States. A recent computer search identified over 250 publications in which CT had been utilized in the dog since 1980. Many papers emanate from research applications of CT, but an ever increasing number of clinical reports involving CT are appearing in the literature. '-lo Before any tool can become an effective diagnostic modality, normal species-specific data must be characterized. Publication of clinically relevant CT anatomy of the dog is basic to effective utilization of this modality in veterinary medicine. Therefore, the purpose of this study was to produce a comprehensive anatomic atlas of CT OMPUTED TOMOGRAPHY
From the Department of Anatomy, Physiological Sciences, and Radiology, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina. Dr. George is currently at the Uniformed Services University of the Health Sciences, 6500 Jones Bridge Road, Bethesda, Maryland 20814. Supported by the State of North Carolina. The authors gratefully acknowledge the competent technical assistance of Steven Holladay, Lisa Cole-Snow, Earl Delsanto, and Janet Allen. Correspondence and reprint requests to James E. Smallwood, DVM, Department of Anatomy, Physiological Sciences, and Radiology, College of Veterinary Medicine, North Carolina State University, Raleigh North Carolina 27606. Received July 17, 1991; accepted for publication September 9, 1991.
anatomy of the dog for use by veterinary radiologists, clinicians, and surgeons. Relatively few papers on normal CT anatomy of dogs are however, Feeney et al. have recently published an atlas of correlative imaging anatomy of the normal dog. l6 Although similar in some respects to the illustrations published in that text, our reference images differ in that the exact position of the dog was maintained from scan to frozen section. In addition, the incorporation of xeroradiographs of the slices serves to bridge the gap between the CT image and the anatomic specimen. The primary advantage of the xeroradiograph is that it provides a full-thickness, radiographic image of the slice, whereas the anatomic section presents only its cut surface for confirmation of structures imaged in the CT section. Thus, even though there is some overlap of our work with that of Feeney et al., we believe that our study includes additional information. We believe that our matched-slice presentation will allow the clinician to evaluate the CT image with an increased ability to identify relevant structures in the area of interest. As one of the primary uses of CT is for the evaluation of mass-like lesions, our reference should be useful in determining the origin of the mass as well as, in some instances, explaining clinical signs. This reference should also be of value to the surgeon in developing an operative plan through a greater awareness of structures in the immediate area.
217
218
GEORGEAND
In this paper, the head and neck of the mesaticephalic (beagle) dog is presented.
Methods Two mature beagles, one male and one female, were used for the study. After physical examination, each dog was anesthetized with a short-acting barbiturate and intubated. Anesthesia was maintained with halothane gas and supplemental fluids were provided. While under anesthesia, the dog was supported in sternal recumbency and a wholebody CT scan was made using a general diagnostic CT system* with a slice thickness of 13 mm. The head was scanned using high-resolution imaging with a slice thickness of 8 mm. At the conclusion of the CT session, the animal was euthanized with an overdose of pentobarbital while still under anesthesia. While carefully maintaining the same position, the body was placed in a walk-in freezer until completely frozen. The body was then sectioned at 13-mm (head at 8-mm) intervals, with the cuts matched as closely as possible to the CT slices. The frozen sections were cleaned, photographed, and radiographed using xeroradiography.? All sections were preserved for future reference. Each CT image was studied and compared with its
*EMI-5005 CT Scanner, EM1 Medical, Inc., Northbrook, IL 60062. ?Xerox 126 System, Xerox Medical Systems, Pasadena, CA 91 107.
1992
SMALLWOOD
corresponding xeroradiograph and anatomic section to assist in the accurate identification of specific structures. Intact, sagittally sectioned, and disarticulated dog skulls were also used as reference models. Clinically relevant anatomic structures were identified and labeled in the three corresponding photographs (CT image, xeroradiograph, and anatomic section).
Results The results of our study consist of the matched photographs presented in the figures. Figure 1 is a drawing of a beagle dog in sternal recumbency with lines indicating the approximate levels of each CT image and anatomic slice of the frozen cadaver. Because the drawing is not an actual reproduction of the two dogs that were used in the study, some of the lines do not correspond exactly with the indicated scan/slice. The lines were angled slightly relative to the long axis of the head in an attempt to more closely approximate the levels of the CT images and anatomic slices. In figures 2-22, the CT image (A), the xeroradiograph of the anatomic slice (B), and the cut surface of the anatomic slice (C) are viewed from caudal to rostra1 (cranial). Because we know of no established standard orientation for the publication of CT images, we chose to orient the CT images and xeroradiographic sections to match the anatomic slices, of which the caudal surfaces were photographed.
FIG. 1. Drawing of beagle dog in sternal recumbent position. Numbered lines indicate the approximate level of each CT scan, corresponding xeroradiograph, and anatomic section shown in figures 2-22.
VOL. 33, No. 4
CT ANATOMY OF HEADAND NECKOF THE DOG
219
FIG.2. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level #2: (1) cartilaginous nasal septum; (2) right superior canine tooth; (3) tongue; (4) intermandibular joint; (5) endotracheal tube; (6) left inferior canine tooth; (7) left superior incisor 3; (8) alar fold.
220
FIG.3. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level #3: (1) right nasal bone; (2) right dorsal nasal concha; (3) vomer; (4) tongue; ( 5 ) right inferior premolar 1; (6) right middle mental foramen; (7) intermandibular joint; (8) left superior canine tooth. The area of increased opacity in the ventral part of the left half of the nasal cavity in the CT image (A) is presumably an imaging artifact. No lesion was found on examination of the anatomic slice (C) of this section.
GEORGE AND SMALLWOOD
1992
VOL. 33, No. 4
CT ANATOMY OF HEADAND NECKOF THE DOG
22 1
FIG. 4. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level #4: (1) left dorsal nasal concha; (2) right ventral nasal concha; (3) vomer; (4) right mandibular canal; ( 5 ) left superior premolar 2; (6) apical part of left superior canine tooth; (7) cartilaginous nasal septum. The area of increased opacity in the ventral part of the left half of the nasal cavity in the CT image (A) is presumably an imaging artifact. No lesion was found on examination of the anatomic slice (C) of this section.
222
FIG.5. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level #5: (1) cartilaginous nasal septum; (2) left infraorbital foramen; (3) left superior premolar 3; (4) left inferior premolar 4; (5) spiral lamella~ofleft ventral concha.
GEORGEAND SMALLWOOD
1992
VOL. 33, No. 4
CT ANATOMY OF HEADAND NECKOF
THE
DOG
223
FIG.6. CT image (A), xeroradiograph (B), and caudal surface of anatomic section ( C ) made at level #6: (1) septa1 processess of nasal bones forming dorsal part of osseous nasal septum; (2) perpendicular lamina of ethmoid bone forming ventral part of osseous nasal septum; (3) right maxillary recess; (4) right orbital lamina of ethmoid bone forming medial wall of 3; ( 5 ) right choana; (6) right superior premolar 4; (7) right inferior molar I; (8) left mandibular canal; (9) vomer; (10) left infraorbital canal; (1 1) ethmoturbinates forming middle nasal concha.
224
FIG.7. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level #7: (1) right medial frontal sinus; ( 2 ) right lateral frontal sinus; (3) lens of right eye; (4) right zygomatic bone; (5) ventral oblique muscle of right eye; (6) right maxillary vessels and nerve approaching maxillary foramen; (7) right choana; (8) horizontal lamina of right palatine bone forming part of hard palate; (9) vomer; ( 10) caudal part of left maxillary recess; (11) perpendicular lamina of ethmoid bone forming ventral part of osseous nasal septum; (12) ethmoturbinates; (13) septa1 processes of frontal bones forming dorsal part of osseous nasal septum.
GEORGE AND SMALLWOOD
I992
VOL. 33, No. 4
CT ANATOMY OF HEADAND NECKOF
THE
DOG
225
FIG.8. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level #8: (1) right medial frontal sinus; (2) internal surface of right frontal bone; (3) right lateral frontal sinus; (4) sclera of right eyeball; (5) right medial pterygoid muscle; ( 6 ) right zygomatic salivary gland; (7) right caudal recess of nasal cavity occupied by endoturbinate IV; (8) right choana at junction with nasopharynx; (9) tongue; (10) left superior molar 2; (1 1) left superior molar 1; (12) vomer; (13) left zygomatic arch; (14) olfactory bulbs of brain lying against cribriform plate of ethmoid bone; (15) zygomatic process of left frontal bone.
226
FIG.9. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level #9 (1) frontal crest formed by united septa1 proceses of frontal bones; (2) frontal lobes of cerebral hemispheres (dorsally) and olfactory bulbs (ventrally); (3) right temporalis muscle; (4) coronoid process of right mandible; ( 5 ) extraocular muscles surrounding right optic nerve and surrounded by intraperiorbital fat; (6) right zygomatic salivary gland; (7) right medial pterygoid muscle; (8) sphenoidal process of right palatine bone; (9) nasopharynx; (10) tongue, containing fat; (1 1) soft palate; (12) left caudal recess of nasal cavity; (13) left masseter muscle; (14) left zygomatic arch; (15) left ventrolateral wall of rostral cranial fossa formed by overlapping sphenoidal process of palatine bone and wing of presphenoid bone; (16) left dorsolateral wall of rostral cranial fossa formed by orbital surface of frontal bone; (17) left lateral frontal sinus; (18) internal surfact of left frontal bone.
GEORGEAND SMALLWOOD
1992
VOL. 33, No. 4
CT ANATOMY OF HEADAND NECKOF THE DOG
227
FIG.10. CT image (A), xeroradiograph (B), andcaudal surface of anatomic section (C) made at level #lo: (1) dorsal sagittal sinus located within falx cerebri; (2) frontal lobe of right cerebral hemisphere; (3) right optic canal containing right optic nerve; (4) right orbital fissure containing right oculomotor, trochlear, ophthalmic, and abducent nerves; (5) right rostral alar foramen containing right maxillary artery and nerve; ( 6 ) right medial pterygoid muscle; (7) hamulus of right pterygoid bone; (8) soft palate; (9) fat within tongue; (10) geniohyoideus muscles; (1 1) left digastricus muscle; (12) nasopharynx; (13) left masseter muscle; (14) left temporalis muscle; (15) left zygomatic arch (16) coronoid process of left mandible; (17) left ventrolateral wall of cranium at junction of rostral and middle cranial fossae formed by basisphenoid bone; (18) left dorsolateral wall of calvaria formed by frontal bone.
228
FIG.11. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level # l l: (1) corpus callosum; (2) parietal lobe of right cerebral hemisphere; (3) thalamus; (4)hippocampus; (5) dorsum sellae; (6) right temporomandibular joint; (7) cavernous sinus surrounding right internal carotid artery; (8) basisphenoid bone; (9) nasopharynx; (10) soft palate; (1 1) fat within tongue; (12) left oval foramen containing left mandibular nerve; (13) angular process of left mandible; (14)condylar process of left mandible; (15) head of left mandible; (16) zygomatic process of left temporal bone; (17) caudal projection of coronoid process of left mandible; (18) left temporalis muscle; (19) left lateral ventricle; (20) left dorsal wall of calvaria formed by parietal bone.
GEORGEAND SMALLWOOD
1992
VOL. 33, No. 4
CT ANATOMY OF HEADA N D NECKOF
THE
DOG
229
FIG. 12. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level #12: (1) dorsal sigittal sinus located within falx cerebri; (2) tentorium osseum cerebelli; (3) parietal lobe of right cerebral hemisphere; (4) hippocampus; (5) petrosal crest of right temporal bone; (6) temporal lobe of right cerebral hemisphere; (7) retroarticular foramen; (8) air within right external acoustic meatus; (9) annular cartilage of right ear; (10) right piriform lobe; (1 1) canal for right trigeminal nerve; (12) right carotid canal; (13) right palatine tonsil; (14) fat within tongue; (15) left ceratohyoid bone; (16) left epihyoid bone; (17) left stylohyoid bone; (18) left mandibular salivary gland; (19) angular process of left mandible; (20) left parotid salivary gland; (21) left tympanic cavity; (22) zygomatic process of left temporal bone; (23) left ventrolateral wall of cranium formed by squamous part of temporal bone; (24) left temporalis muscle; (25) left dorsolateral wall of calvaria formed by parietal bone; (26) left lateral ventricle.
230
FIG. 13. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level #13: (1) temporal line; (2) dorsal sagittal sinus located within falx cerebri; (3) tentorium osseum cerebelli; (4) temporal meatus containing temporal sinus; ( 5 ) annular cartilage of right ear; ( 6 ) cerebellar fossa containing paraflocculus of right cerebellar hemisphere; (7)right longus capitis muscle; (8) nasopharynx; (9) soft palate; (10) epiglottic cartilage; (1 1) basihyoid bone; (12) left ceratohyoid bone; (13) oropharynx; (14) left mandibular salivary gland; (1 5) left stylohyoid bone; (16) left tympanic cavity; (17) left malleus; (18) left external acoustic meatus; (19) left petrous temporal bone; (20) scutiform cartilage of left ear; (21) left temporalis muscle; (22) vermis of cerebellum; (23) occipital lobe of left cerebral hemisphere; (24) interparietal bone.
GEORGEAND SMALLWOOD
1992
VOL. 33, No. 4
CT ANATOMY OF HEADAND NECKOF
THE
DOG
23 1
FIG. 14. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level #14: (1) external occipital protuberance; (2) tentorium 0 s seum cerebelli; (3) right transverse sinus canal containing transverse sinus; (4) paraflocculus of right cerebellar hemisphere; (5) right condylar canal containing condylar vein; ( 6 )right stylomastoid foramen containing right facial nerve; (7) fourth ventricle; (8) myelencephalon; (9) right longus capitis muscle; (10) pharyngeal constrictor muscles; (11) right thyrohyoid bone; (12) epiglottic cartilage; (13) basihyoid bone; (14) oropharynx; (15) left mandibular salivary gland; (16) junction of left tympanic bulla and paracondylar process; (17) left mastoid process of temporal bone; (18) left temporalis muscle; (19) vermis of cerebellum; (20) occipital lobe of left cerebral hemisphere.
232
FIG.15. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level # 15: (1) external occipital protuberance; (2) groove for right transverse sinus; (3) right internal occipital crest; (4) fourth ventricle; ( 5 ) right occipital condyle; ( 6 )myelencephalon; (7) right paracondylar process of occipital bone; (8) right longus capitis muscle; (9) pharyngeal constrictor muscles; (10) right thyrohyoid bone; (1 1) right laryngeal ventricle; (12) right sternohyoideus muscle; (13) left vocal fold; (14) left medial retropharyngeal lymph node; (15) left mandibular salivary gland; (16) left common carotid artery; (17) interbasilar sinus; (18) foramen magnum; (19) vermis of cerebellum projecting into vermiform impression of occipital bone; (20) foramen for dorsal sagittal sinus.
GEORGEAND SMALLWOOD
1992
234
FIG.17. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level #17: (1) rhomboideus capitis muscle; (2) cervical spinal cord segments 2 & 3; (3) right obliquus capitis dorsalis muscle; (4)right transverse foramen of atlas containing vertebral vessels & nerve; (5) right ventral internal vertebral plexus; ( 6 )right cleidomastoideus muscle; (7) right common carotid artery; (8) right external jugular vein; (9) right longus colli muscle; (10) right caudal cornu of thyroid cartilage; (1 1) cricoid cartilage; (12) laryngopharynx; (13) left wing of atlas; (14) left splenius cervicis muscle; (15) spinous process of axis.
GEORGEAND SMALLWOOD
1992
VOL. 33, No. 4
CT ANATOMY OF HEADAND NECKOF THE DOG
235
FIG. 18. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level #18: (1) spinous process of axis; (2) right semispinalis capitis muscle; (3) right splenius cervicis muscle; (4) caudal border of right wing of atlas; ( 5 ) right omotranversarius muscle; (6) right cleidomastoideus muscle; (7) right common carotid artery; (8) right external jugular vein; (9) right sternomastoideus muscle; (10) lamina of cricoid cartilage; ( 1 1) left sternothyroideus muscle; (12) junction of laryngopharynx and esophagus; (15) stemooccipitalis muscle; (14) cervical spinal cord segment 3.
236
FIG.19. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level #19: (1) right caudal articular process of axis; (2) right splenius cervicis muscle; ( 3 ) right semispinalis capitis muscle; (4) right cranial articular process of C3; ( 5 ) right transverse process of C3; (6) right longus capitis muscle; (7) right common carotid artery; (8) right lobe of thyroid gland; (9) inflated endotracheal tube cuff within tracheal lumen; (10) esophagus; (1 1) left cleidomastoideus muscle; ( 12) left longus colli muscle; ( 13) cervical spinal cord segment 4.
GEORGEAND SMALLWOOD
1992
VOL. 33, No. 4
CT ANATOMY OF HEADAND NECKOF
THE
DOG
237
FIG.20. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level #20: (1) nuchal ligament; (2) right semispinalis capitis rnuscle; (3) right splenius cervicis muscle; (4) right caudal articular process of C3; (5) right transverse foramen of C3, containing vertebral vessels & nerve; (6) right transverse process of C3; (7) right sterno-occipitalismuscle; (8) right sternomastoideus muscle (9) right longus capitis muscle; (10) right sternothyroideusmuscle; (1 1 ) tracheal cartilage; (12) esophagus; (13) left common carotid artery; (14) left transverse process of C4; (15) left cranial articular process of C4; (16) cervical spinal cord segments 3 & 4; (17) combined left multifidus & spinalis cervicis muscles.
238
FIG.21. CT image (A), xeroradiograph (B), and caudal surface of anatomic section (C) made at level #21: (1) nuchal ligament; (2) spinous process of C4; (3) right transverse foramen of C4, containing vertebral vessels & nerve; (4) right clavicle embedded in brachiocephalicus muscle; ( 5 ) deltoid tuberosity of right humerus; (6) right transverse process of C5; (7) right external jugular vein; (8) right common carotid artery; (9) tracheal cartilage; (10) left sternocephalicus muscle; (1 1) esophagus; (12) left longus capitis muscle; (13) left transverse process of C4; (14) cervical spinal cord segments 4 & 5.
GEORGEAND SMALLWOOD
1992
VOL. 33, No. 4
CT ANATOMY OF HEADAND NECKOF
THE
DOG
239
FIG.22. CT image (A),xeroradiograph (B), and caudal surface of anatomic section (C)made at level #22: (1) nuchal ligament; (2) right spinalis cervicis muscle; (3) right trapezius cervicis muscle; (4) supraglenoid tubercle of right scapula; (5)greater tubercle of right humerus; ( 6 ) acromion of right scapula; (7) right transverse foramen, containing vertebral vessels & nerve, (8) right ascending (deep) pectoral muscle; (9) right external jugular vein; (10)combined right stemothyroideus and stemohyoideus muscles; (1 1) tracheal cartilage; (12) left transverse (superficial) pectoral muscle; (13) esophagus; (14)left transverse process of C5;(15)lesser tubercle of left humerus; (16) cervical spinal cord segment 6; (17) spinous process of C5.
240
GEORGE AND SMALLWOOD
1992
REFERENCES 1. Emms SG, Wortman JA, Johnston DE, Goldschmidt MH. Evalu-
ation of canine hyperadrenocorticism using computed tomography. JAVMA 1986;189:432-439. 2. Bailey MQ. Use of x-ray-computed tomography as an aid in localization of adrenal masses in the dog. JAVMA 1986;188:104CL1049. 3. Turrel JM, Fike JR, LeCouteur RA, Higgins RJ. Computed tomographic characteristics of primary brain tumors in 50 dogs. JAVMA 1986;188:851-856. 4. Kay ND, Holliday TA, Hornof WJ, Gomez J. Diagnosis and management of an atypical case of canine hydrocephalus using computed tomography, ventriculoperitoneal shunting, and nuclear scintigraphy . JAVMA 1986:423-426. 5 . Chrisman CL, Spencer CP, Crane SW, et al. Late-onset cerebellar degeneration in a dog. JAVMA 1983;182717-720. 6. Swengel JR. Computerized tomography for diagnosis of brain tumor in a dog. JAVMA 1981;181: 605. 7. LeCouteur RA, Fike JR, Scagliotti RH, Cann CE. Computed tomography of orbital tumors in the dog. JAVMA 1982;180:910-913. 8. Mandelker L. Using computed brain and orbital tomography to diagnose a brain tumor in a dog. VM SAC 1981;76:11641167.
9. Fike JR, LeCouteur RA, Cann CE, Pflugfelder CM. Computerized tomography of brain tumors of the rostra1 and middle fossas in the dog. AJVR 1981;42:275-281. 10. LeCouteur RA, Fike JR, Cann CE, Pedroia VG. Computed tomography of brain tumors in the caudal fossa of the dog. Vet Radiol 1981;22: 244-251. 11. Fike JR, LeCouteur RA, Cann CE. Anatomy of the canine orbital region multiplanar imaging by CT. Vet Radiol 1984;25:32-36. 12. Kaufman HH, Cohen G, Glass TF, et al. CT atlas of the dog brain. J Comput Assist Tomogr 1981;5:529-537. 13. Zook BC, Hitzelberg RA, Fike JR, Bradley EW. Anatomy of the beagle in cross-section: head and neck. AJVR 1981;42:844-849. 14. Fike JR, LeCouteur RA, Cann CE. Anatomy of the canine brain using high resolution computed tomography. Vet Radiol 1981;22:236243. 15. Fike JR, Druy EM, Zook BC, et al. Canine anatomy assisted by computerized tomography. Am J Vet Res 1980;41:1823-1832. 16. Feeney DA, Fletcher TF, Hardy RM, Atlas of correlative imaging anatomy of the normal dog, ultrasound and computed tomography, Philadelphia: WB Saunders, 1991.
