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Diseases of the Nasal Cavity and Paranasal Sinuses
Diseases of the Nasal Cavity and Paranasal Sinuses
C H A P T E R
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THOMAS H. WITTE
CLINICALLY RELEVANT ANATOMY AND PHYSIOLOGY
The rostral extent of the nasal cavities, the external nares, is supported by cartilage and muscle. This makes them mobile and flexible, allowing for sealing of the nasal cavity during swimming and widening at maximal exercise, but also allowing for pathologic collapse when there is neuromuscular dysfunction. The clinically significant landmarks of this region include the nasolacrimal ostium at the ventral aspect at the mucocutaneous junction, which is easily cannulated there, and the nasal diverticula, or false nostrils. These blindending, hair-lined pockets are closely associated with the lateral aspect of the external nares, from which they are separated by the alar cartilages. Continuing caudally, the midline cartilaginous nasal septum divides the nasal cavity into left and right halves. These cavities are further subdivided by the dorsal and ventral turbinates into the dorsal, middle, ventral, and common meatus (Figure 50-1). The turbinates are scrolled bones that project into the nasal cavity from the lateral wall. The internal space within each scroll is divided into rostral and caudal cavities. The rostral components are termed recesses and are less clinically significant than the caudal components, which form the dorsal and ventral conchal sinuses and communicate with the frontal and rostral maxillary sinuses, respectively. The submucosa of the nasal cavity is highly vascular, in keeping with the function of warming and humidifying inspired air. Because the nasal cavity is encased in rigid bone, any space-occupying lesion here will have a marked impact on airflow and hence athletic performance. Simple vascular congestion caused by iatrogenic jugular thrombophlebitis or loss of sympathetic tone in Horner’s syndrome can be performance limiting and, if left undetected, will limit the success of other upper respiratory tract interventions. The caudal extent of the nasal cavity is bounded dorsally by the middle turbinate, which is surrounded on its caudal aspect by the fine, highly vascular cartilaginous ethmoturbinate scrolls, collectively termed the ethmoidal labyrinth. The increased surface area provided by the labyrinth is lined with olfactory epithelium and with sensory neurons whose axons converge to form the olfactory nerve (cranial nerve [CN] I). Although the integrity of the cribriform plate caudal to the ethmoid is crucial when considering treatment options in this area, it cannot be examined endoscopically in the normal horse. The paranasal sinuses lie lateral and dorsal to the nasal cavity, and although they are made up of six paired chambers, they can be considered as two functional compartments: rostral and caudal. The two compartments drain separately to the middle meatus through the rostral and caudal maxillary sinuses and a common aperture. The nasomaxillary aperture cannot be seen directly with standard endoscopic techniques and equipment, and under normal
circumstances, the paranasal sinuses cannot be accessed directly through the nose. Endoscopic evidence of sinus disease is therefore often limited to fluid egress at the drainage angle of dorsal and ventral turbinates in the dorsal nasopharynx, rostral to the middle turbinate. The caudal paranasal compartment consists of frontal, dorsal conchal, caudal maxillary, and sphenopalatine sinuses. The rostral compartment, which is separated from the caudal compartment by the oblique, curved maxillary septum and its dorsal continuation as the bulla of the ventral conchal sinus, consists of rostral maxillary and ventral conchal sinuses. The rostral maxillary and ventral conchal sinuses communicate over the infraorbital canal and are separated ventrally by the septum that supports this structure, or the maxillary cheek teeth, depending on the age of the horse (see Figure 50-1). The caudal outpouching of the ventral conchal sinus is known as the bulla of the ventral conchal sinus and represents a key surgical landmark. The channel for drainage from both the caudal and rostral sinus compartments into the middle meatus is closely associated with this structure. The conjoined sphenoidal and palatine sinuses (known as the sphenopalatine sinus) extend under the ethmoid and the base of the skull (see Color Plate 50-1). Any space-occupying lesion in this area can cause compression of the optic nerves, brain, and pituitary gland, resulting in unusual presenting complaints. Health of the paranasal sinuses in any species relies on adequate ventilation through the natural ostia and on mucociliary transport provided by ciliated columnar epithelium. The mucociliary escalator works toward the natural drainage channels from the rostral and caudal maxillary sinuses, maintaining a continuous protective mucus layer flowing out of the sinuses. This flow is aided by gravity when the head is down, but continues against gravity at other times. The narrow drainage channels are easily obstructed and distorted by primary disease processes, and the resultant impaired drainage must be recognized and addressed. Surgical interventions should be planned carefully with the goal of maintaining or restoring normal mucociliary clearance from the dependent sinuses, rather than creating new drainage ostia in a separate location. Termed functional sinus surgery in humans, this approach aims to be mucosa sparing when possible. The evolution of endoscopic techniques has contributed to the revolution in surgery of the paranasal sinuses. The relationship between the cheek teeth and the paranasal sinuses is clinically significant. Part of the upper Triadan 08 tooth and the entire root system of the 09 are usually associated with the floor of the rostral maxillary sinus, whereas the roots of the 10 and 11 are associated with the floor of the caudal maxillary sinus (see Color Plate 50-1). Periapical disease of these teeth commonly results in secondary sinusitis, compared with periapical disease of the more
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FS DCS MM VCS RMS
110
The nares should be dry and free from crusting, except for a small volume of tears evident at the nasolacrimal ostium. Airflow should be tested at the external nares; subtle differences may be more obvious after temporary occlusion of airflow or by the use of strands of cotton to detect airflow. Horses with restricted airflow at any level of the respiratory tract may dilate their nostrils bilaterally. The nostrils should remain mobile and tactile and respond to internal and external palpation. Deformation of the facial contour over the paranasal sinuses indicates pressure buildup within the sinuses and most commonly points to a space-occupying lesion such as a cyst or neoplasia. Severe secondary sinusitis cannot, however, be ruled out as a cause of facial distortion because complete occlusion of drainage can result in sufficient pressure to cause distortion. Although percussion of the sinuses for fluid- or soft tissue–induced dullness and palpation of the lymph nodes should form part of any routine physical examination of the head, the findings are often equivocal and difficult to interpret definitively.
Endoscopy
Figure 50-1 Transverse computed tomogram of the nasal cavity and paranasal sinuses at the level of tooth 110. FS and DCS, frontal and dorsal conchal sinuses, respectively, often referred to as the combined conchofrontal sinus; MM, middle meatus; RMS, rostral maxillary sinus; VCS, ventral conchal sinus. Curved arrow indicates drainage channel from the rostral maxillary sinus; notice the relationship to the ventral turbinate and floor of the frontal sinus. A circle of bone encompasses the infraorbital canal; notice its relationship to the RMS, VCS, and maxillary cheek teeth.
rostral teeth (06 to 08), in which facial swelling or external draining tracts are more common. The proximity of the teeth makes trephination of the maxillary sinuses difficult and often unrewarding, particularly in the young horse when the reserve crowns are large and the sinus cavities small. The precise relationship between the apices of the cheek teeth and the respective sinuses cannot be predicted on the basis of plain radiographs: disease of the 08 and 09 teeth can result in sinusitis of the caudal compartment if there is rostral extension of the caudal maxillary sinus and obliquity of the maxillary septum, whereas apical disease of the 10 and 11 teeth can result in sinusitis of the rostral compartments when there is caudal extension of the ventral conchal sinus. Attempting to predict which tooth is infected based on which sinuses are diseased should be avoided.
EXAMINATION
Historical Findings Horses with sinonasal disease can have clinical signs ranging from subtle poor performance, epiphora, or head shaking to the more common nasal discharge, facial swelling, and difficult breathing. Because many horses are not presented until the signs are obvious, disease can be at an advanced stage by the time the horse is first evaluated. Understanding the progression historically can be vital to establishing a valid differential diagnosis list and ensuring that appropriate diagnostic tests are undertaken. In particular, changes in the volume, odor, timing, nature, duration, and laterality of discharge over time can be extremely informative.
Physical Examination The head should be evaluated from both sides and in front for symmetry and swellings as well as for pain on palpation.
Endoscopic examination for nasal and paranasal sinus disease may include rhinoscopy, dentoscopy, and sinoscopy. Rhinoscopy can be performed with a standard flexible endoscope. A videoendoscope allows documentation of findings for serial evaluations and can be particularly helpful in treatment of mass lesions. In the presence of active discharge from the nose, rhinoscopy will confirm the source of the drainage. Routine rhinoscopy should include careful evaluation of the nasopharynx, ethmoidal labyrinth, drainage angle between dorsal and ventral turbinates, and mucosa of the dorsal, ventral, and middle meatus. Dentoscopy or examination of the dental occlusal surfaces with a mirror should be undertaken in any horse with unilateral nasal discharge of unknown etiology and must involve a thorough assessment of the periodontium. Careful documentation of findings enables serial monitoring and helps in client communication. Sinoscopy has become less critical as a diagnostic modality for paranasal sinus disease with the advent and availability of standing computed tomography (CT), although it remains a key tool therapeutically and a cornerstone of the diagnostic process if CT is unavailable. Several approaches to each of the sinus compartments have been described, but the most universal appears to be creation of a frontal sinus portal of an appropriate size to allow a flexible endoscope to be inserted, with or without space to pass an instrument alongside depending on surgeon preference (see Color Plate 50-1). Primary approaches to the maxillary sinuses pose the risk for iatrogenic damage to the cheek teeth and are less useful in gleaning an overview of the global disease state, although they may still be very useful therapeutically when they can be placed under sinoscopic guidance or with the benefit of CT. Sinoscopy is performed in the standing sedated horse, making orientation easier and preventing loss of visibility in the presence of bleeding. Suction should be available if possible. A Galt trephine is used to cut a circular disk of bone from the bone plate. Frequent lavage of the site will prevent the buildup of bone dust subcutaneously and minimize postoperative reaction. A 2.5-cm-diameter trephine appears to be the optimal size because this allows an instrument to be passed alongside the endoscope, avoiding the necessity for a second portal, while not being too large for a good cosmetic outcome. Creating two separate 1-cm trephine holes for the endoscope and instrument is also suitable. The frontonasal suture line should be avoided when possible (see Color Plate 50-2). In general, this suture line runs between the medial
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50 Diseases of the Nasal Cavity and Paranasal Sinuses
canthi of the eyes, and placing a trephine or other osteotomy across this line, which becomes more likely with increasing osteotomy size, results in more or less severe suture periostitis. The standard approach to the frontal sinus, caudal to and midway along a line drawn perpendicular to the midline at the level of the medial canthus of the eye, allows the caudal maxillary and conchofrontal sinuses to be explored directly without risk for damage to the intrasinus component of the ethmoid during the approach. Damage to the latter results in profuse hemorrhage, making accurate diagnosis and intervention more difficult. From the frontal sinus, the endoscope can be passed freely through the large frontomaxillary aperture into the caudal maxillary sinus (see Color Plate 50-1). The ventral conchal bulla, the caudal outpouching of the ventral conchal sinus, lies beneath the rostral margin of the frontomaxillary aperture. This cartilaginous bulla, which varies among horses in shape and size and can appear to be absent in horses with chronic deformation of the intrasinus anatomy, can be resected to give access to the rostral maxillary and ventral conchal sinuses. The ventral conchal sinus is often the site of mucus inspissation in cases of chronic sinusitis, and this condition can be confirmed and treated by this approach. When necessary, the frontal portal can be supplemented with a maxillary trephine, which can safely be created under endoscopic guidance and transillumination. Postoperative lavage tubes can be placed through the frontal sinus portal, allowing adequate lavage without creating any further trephines. The pressure of postoperative lavage fluid must be carefully controlled to avoid subcutaneous accumulation of fluid, especially with larger osteotomies.
DIAGNOSTIC IMAGING
Standard lateral and oblique radiographic views of the paranasal sinuses provide a useful baseline, although more specialized views, including intraoral and open-mouth radiographs, are necessary to gain a more complete understanding of the underlying pathology. A dorsoventral view is particularly useful to identify opacification of the ventral conchal sinus or deviation of the nasal septum. Internal dental architecture can also be visualized if the mandibular and maxillary arcades can be offset. Numerous other special projections have been described for imaging the cheek teeth without superimposition and are based on an understanding of the curvature of the dental arcade and the caudal-to-rostral narrowing evident when one carefully examines the equine skull. The ideal projection to isolate the maxillary cheek teeth is thus taken 15 degrees caudal to the straight lateral and 30 degrees dorsal to the horizontal axis. Nuclear scintigraphy can be helpful in determining the clinical significance of a radiographic finding or, more often, can create a suspicion of dental or sinus origin for spurious or vague presenting signs. Lateral and dorsoventral scintigraphic views of the head are easy to acquire and, depending on signalment and history, may form part of any full-body bone scan performed for poor performance. Ultimately, in difficult, refractory, or recurrent cases, referral for CT may be considered necessary, in particular where this modality is available for the standing horse. This technique is considered the gold standard for complete evaluation of intrasinus space-occupying lesions, particularly when neoplasia is suspected, and for the definitive detection of dental pathology. Computed tomography offers advantages in surgical planning, enabling the examiner to identify the relationship between diseased areas and important structures such as the infraorbital nerve, nasolacrimal duct, and cribriform plate. This information allows the application of advanced, minimally invasive, and functional
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endoscopic techniques for the treatment of the full range of sinus diseases.
DISEASES OF THE NASAL CAVITY Epidermal Inclusion Cysts
The term atheroma is sometimes inappropriately used to describe the variably sized soft, fluctuant swellings found within the nasal diverticulum in horses around the age of 2 years. These swellings are epidermal inclusion cysts that enlarge continuously from exfoliation of squamous cells from their lining. Most commonly these lesions do not threaten the lumen of the airway because they bulge laterally, and their significance is rarely anything more than cosmetic. Diagnosis is based on the pathognomonic location and gross appearance of the lesion, and aspiration yields a gray, odorless, greasy fluid. The masses can be removed intact through an external skin incision, and injection of formalin has been reported, but the most predictable cosmetic outcome is achieved by incising and removing the cyst lining with a ventriculectomy burr placed through the external nares.
Alar Fold Collapse Alar fold collapse causes an abnormal upper respiratory tract noise that must be differentiated from laryngeal and pharyngeal dysfunction. The noise may be heard at rest or may only be elicited by intense exercise, and has variously been described as a muffled rattling or vibrating noise heard during both inspiration and expiration. Horses may be presented for evaluation primarily because of the noise or because of poor performance. Dynamic respiratory endoscopy can be useful in ruling out other causes of abnormal upper respiratory tract noise and poor performance, but definitive diagnosis necessitates temporary retraction of the alar folds with sutures. By use of a twitch and local anesthesia, suture material is placed through each alar fold and tied dorsally over the nasal bones, occluding the nasal diverticula. Absence of noise after suture placement and recurrence with suture removal provides a definitive diagnosis and justifies surgical resection of the alar folds. Surgery can be performed with the horse anesthetized and positioned in dorsal or lateral recumbency, or with the horse standing. The procedure can be performed through an intact nostril, but some surgeons prefer to incise the lateral alae of the nostrils to expose the alar folds more completely and to ensure complete resection of all associated tissue.
Wounds of the External Nares When left to heal by second intention, wounds of the external nares can deform the contour, flexibility, and function of the nostril. To preserve function and cosmesis, careful reconstruction can be undertaken with a three-layer closure after debridement, when necessary. Only rarely, in the presence of severe contamination or maceration of tissue, must such injuries be left to heal by second intention or, preferably, be closed with delayed primary closure.
Lateral Deviation of the Nose Congenital lateral deviation of the nose, so-called wry nose, has an unknown etiology. Intrauterine factors have been purported to contribute, and a genetic predisposition seems likely, with Arab horses overrepresented. Commonly affecting the maxillary, nasal, and incisive bones and the nasal septum, the deviation has a profound effect on respiration. The effect on the foal’s ability to suckle is less predictable, but when suckling is affected, a concomitant cleft palate must be ruled out. Surgical correction of wry nose through
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multiple osteotomies is a technical challenge but can in rare cases result in an athletic career. Preservation of such animals as breeding stock should be questioned, but they may be suitable for pleasure riding.
Imperforate Buccopharyngeal Septum An imperforate buccopharyngeal septum, also known as choanal atresia, can result in a range of clinical signs, from apparent stillbirth in foals to abnormal respiratory noise during exercise in adults. The buccopharyngeal septum separates the nasal cavity from the nasopharynx in the developing embryo, and its remnant may be unilateral or bilateral, complete or incomplete, and membranous or bony, which explains the diversity of clinical signs. In the neonate, inspiratory stridor and bulging of the guttural pouches may be evident, and temporary tracheostomy may be required to stabilize the patient. Inability to advance a nasogastric tube beyond the nasal passage may alert the clinician to the airway obstruction, and definitive diagnosis is achieved endoscopically or by contrast radiography. Resection has been attempted through a variety of approaches, from endoscope-guided approaches through the nose for membranous obstructions to facial bone osteotomies for bony obstructions. The latter must be performed with caution in the growing animal because growth will almost certainly be impaired after interference with the suture lines, and deformity will result. Maintaining patency after fenestration presents one of the largest challenges, and repeated procedures are necessary in many cases.
Mycotic Rhinitis Infection of the nasal and paranasal mucosa by normally saprophytic fungi such as Aspergillus fumigatus and Pseudallescheria boydii commonly occurs secondary to previous damage such as traumatic injury or surgery. However, cases in which a primary underlying cause cannot be identified are not unusual. Stabled horses that are exposed to moldy hay and straw are likely to be predisposed to mycotic rhinitis. Typical presenting signs include unilateral malodorous mucopurulent nasal discharge. Intermittent mild epistaxis is occasionally seen. Definitive diagnosis is usually straightforward, based on the characteristic appearance of the plaques; however, cytologic examination and fungal culture of the plaques are still recommended, and these appear to yield superior results to those obtained with collection and culture of the exudate. Treatment involves resolution of primary disease, removal of fungal plaques, and topical application of antifungals. Drugs effective against Aspergillus spp include itraconazole, fluconazole, enilconazole, miconazole, ketoconazole, natamycin, clotrimazole, and amphotericin. These may be administered in powder or liquid form, although availability may vary. Administration of the powder form of medication offers advantages with regard to duration of contact, but application can be more challenging.
DISEASES OF THE PARANASAL SINUSES
Diseases of the paranasal sinuses can be thought of as primary infections, secondary infections, and space-occupying lesions, with overlap existing between the categories.
Infectious Sinusitis Primary infections of the sinus commonly follow more generalized infections of the upper respiratory tract. The most common bacterial isolates are members of the streptococcal family, particularly Streptococcus equi subsp equi and zooepidemicus. Primary sinusitis can affect any age group and
generally involves all sinus cavities. If treated promptly and effectively, the medium- to long-term consequences are negligible; however, if the process becomes chronic with mucus inspissation in the ventral conchal sinus, the condition may only be successfully treated by surgery. The diagnosis of primary sinusitis is often made presumptively after endoscopic confirmation of the sinus as the source of an active nasal discharge. Horizontal fluid lines within the sinuses on lateral and oblique radiographs can help further localize the disease process. In the worst cases, with long-standing disease and inadequate drainage, opacification may be extensive, making differentiation from space-occupying lesions difficult. Sinocentesis may be helpful and can be combined with sinus lavage (see Color Plate 50-2). Simple sinocentesis can be performed with a 14-gauge needle tapped through the bone with a mallet, or a dog urinary catheter may be inserted through a hole created with a small Steinmann pin and Jacob’s chuck. The results of cytologic examination and culture may aid in ruling out underlying pathology. Culture of a single bacterial species indicates that the sinusitis is most likely caused by primary bacterial infection. When multiple bacteria are identified or plant material is seen macroscopically or microscopically, periapical dental infection or an orosinus fistula should be suspected. In acute cases of primary sinusitis, empirical treatment with broad-spectrum antimicrobials and antiinflammatories may be effective alone or in combination with simple sinus lavage. During lavage, the clinician should assess the patency of the drainage channel and thereby the likelihood of response to conservative management. After treatment, it may be unclear whether the disease has resolved or the clinical signs have merely been suppressed. Recurrence of signs should prompt further investigation for an underlying primary cause or inspissation. In more chronic cases in which fluid is inspissated or drainage has been impaired, sinoscopy should be performed through a frontal sinus portal as described to remove inspissated material and enlarge the drainage channel if necessary (Figure 50-2). The author routinely resects the bulla of the ventral conchal sinus in all cases to allow direct lavage of both caudal and rostral spaces from a single frontal portal postoperatively. This also allows access to inspissated material in the ventral conchal sinus. Resection of the bulla will enhance drainage to the middle meatus, and in cases in which drainage is severely impaired, dissection can be continued medially and ventrally to remove the dorsal margin of the free wall of the ventral turbinate and enlarge the ostium. In line with a mucosa-sparing functional approach, this is preferred to the creation of artificial drainage at a separate location, such as ventrally within the ventral conchal sinus. The latter approach is more traumatic, is more likely to result in excessive scar tissue, and does not reestablish mucociliary clearance through the normal apertures. It is also more difficult to perform in the standing horse without inducing substantial hemorrhage and the need for postoperative tamponade. Even in chronic cases with severe distortion, enlargement of natural drainage is possible and preferred.
Chronic Sinusitis The most common cause of secondary infections of the sinuses is dental disease, with one half of all sinusitis cases originating from apical infections of the maxillary cheek teeth, diastemata with severe periodontal disease, idiopathic dental fractures, and displaced or supernumerary cheek teeth (Figure 50-3).
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SPS CMS
RMS VCS VCS
108
A
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Figure 50-2 Inspissated material in the ventral conchal sinus (VCS), associated with pulpitis and periapical disease of tooth 108. Notice the presence of gas (black) within the pulp chambers of 108 (A), indicative of pulpitis, and widening of the alveolar space, indicative of periapical disease. Although the primary disease process is in the rostral compartment, opacification of the caudal maxillary (CMS) and sphenopalatine (SPS) sinuses can be seen resulting from occlusion of drainage from the caudal compartments secondary to distortion of drainage anatomy around the bulla of the ventral conchal sinus. The nature of the fluid was anticipated from CT findings and was confirmed on sinoscopic evaluation. The VCS was filled with inspissated material and the CMS and SPS with nonseptic sinus fluid. This case highlights the importance of reestablishing drainage from all sinus compartments, particularly when the internal architecture is distorted.
B
Horses with sinusitis originating from periapical infection of the cheek teeth often have a protracted history of uni lateral nasal discharge. Some response to antimicrobial administration may be seen, but malodorous mucopurulent unilateral nasal discharge returns when treatment is discontinued. A foul odor is a common feature of this condition, but is by no means pathognomonic for periapical tooth infection because it can occur with any disease process in which tissue necrosis is a feature. The caudal cheek teeth (08 to 11) are most often implicated in sinusitis, whereas apical disease of the rostral teeth (06 to 08) most commonly results in facial swelling or draining tracts. This general rule is not fail-safe, however, and presenting signs will depend on the rostral-caudal extension of the individual sinus compartments. Extension of periapical disease and hence drainage directly into the nasal cavity is also possible. Rhinoscopic findings do not help differentiate primary from secondary sinusitis. An oral cavity examination should be completed in all cases of sinusitis that do not respond to initial conservative management. However, the presence or absence of occlusal surface findings does not always confirm or rule out a dental etiology. Extreme care must therefore be taken to ensure that radical and irreversible treatments such as dental extraction are only undertaken when a tooth can be definitively identified as the cause of sinus disease. Radiographs can provide additional clues, in particular periapical osteolysis surrounded by a zone of sclerosis, blunting of tooth roots, and loss of definition of the lamina dura denta, but radiographic changes are notoriously insensitive. A variety of oblique, open-mouth, and intraoral views can be used to image the internal architecture of the teeth and help reach a more definitive diagnosis. Scintigraphy is more sen sitive for identifying an active process but has also been superseded by CT. Computed tomography is now routinely performed in the sedated, standing horse, enabling the entire process of diagnosis and treatment to be completed without the need for general anesthesia. Computed tomography allows assessment of periapical changes to the lamina dura denta and surrounding bone, as well as abnormalities of the internal anatomy of the tooth, such as pulpitis with gas accumulation, widening of the pulp chambers, irregularity
S 211 210 209 208 207 206
Figure 50-3 Developmental dental abnormalities: a supernumerary tooth (S) is visible at position 212. Small arrows delineate periodontal pocketing of feed material and opacification of the associated caudal and rostral maxillary sinuses (compare with normal right side). In this instance, removal of the tooth was necessary to resolve sinusitis and periodontal disease, but this is not always the case. Such supplemental teeth, which resemble normal teeth, must be differentiated from connate teeth, in which the tooth is composed of multiple tooth elements arising from a single alveolus. The latter are more difficult to extract and may not need extraction. Computed tomography helps to clearly define the disease process and to establish a clear dental origin for the presenting signs before extraction is considered.
of the walls of the chambers, and enamel breech between infundibulum and pulp in the case of extensive infundibular caries or cemental hypoplasia (see Figure 50-2). Resolution of sinusitis relies on definitive identification and treatment of all underlying pathology. In the case of
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dental sinusitis, current best practice in the absence of good evidence for dental preservation of infected cheek teeth is dental extraction. Oral extraction techniques enable this to be completed in the standing patient without recourse to approaches through the sinus. Wide sinus exposures, such as flap osteotomies or large trephine holes, are no longer considered necessary for dental extraction, except in very rare cases of extreme displacement and in intractable patients who do not allow work in the standing position through the mouth. One of the most important advantages of oral extraction is retention of an intact alveolar bone plate, negating the need for a watertight seal of the alveolus, as would be the case after tooth repulsion when there is a real risk for orosinus fistula formation. After oral extraction, the alveolus should be packed with gauze dressing impregnated with a dilute povidone-iodine solution for the first few days. The goal is to retain the initial alveolar hematoma within the socket and to protect the socket during the initial inflammatory phase of healing. Packing is not required beyond the first 5 days. Granulation of the alveolus can be promoted by applying very strong iodine or other irritant agents to the socket; however, this is considered unnecessary and may even promote sequestration of the alveolar wall. In nonsinusitis cases, fracture of the tooth during extraction may not necessitate complete fragment retrieval, but in cases with more extensive and apical pathology and in those with sinusitis, dental remnants are often sufficient to incite ongoing clinical signs and must be retrieved (Figure 50-4). A variety of oral and minimally invasive approaches exist to achieve this, including mini-buccotomy with screw extraction and mini-trephine and repulsion with a Steinmann pin, both of which can be performed in a standing sedated horse. Alongside dental extraction, the sinuses most often require lavage,
and this can most easily be achieved through a sinoscopic approach as described earlier. This helps to confirm the diagnosis of dental pathology and allows adequate drainage to be ensured. It is performed before dental extraction in the same sedative episode in most cases. Systemic antimicrobials and antiinflammatories should be used in the first 5 days after extraction, particularly in more involved cases in which surgical trauma is substantial. Orosinus fistulae are a substantial risk after dental repulsion, in contrast to oral extraction, in which the alveolar bone plate remains intact. Sequestration of the alveolar wall or dental remnants can result in delayed healing, or the dental plug may be lost prematurely before the alveolus has healed, resulting in contamination of the sinus with feed material. The hallmark clinical signs are sudden recurrence of severe nasal discharge, often with feed material evident at the external nares. Management should be directed at achieving an accurate and complete diagnosis of the underlying pathology. Sequestration of bone or tooth must be ruled out. When available, CT provides a more complete understanding of the causes of fistula formation and enables more definitive treatment, often using minimally invasive approaches (see Figure 50-4). In the absence of such a complete diagnosis, an empirical approach is to perform maxillary flap sinusotomy to provide wide exposure to the affected alveolus for sequestrectomy and debridement. The socket is packed with dental impression material or equivalent from the oral side to create a seal. Thorough lavage and confirmation of adequate drainage from an often severely inflamed sinus are also critical. If conservative approaches fail or in the case of large mature defects, muscle transposition can be performed by a variety of approaches. The risk for fistulation is increased if two adjacent teeth require extraction. The teeth can be removed
CMS VCS RMS RMS
Figure 50-4 A single large and multiple small tooth fragments (large arrows) within the 109 and 209 alveoli, respectively. The fragments were left after the teeth were incompletely extracted through the oral cavity, and led to chronic bilateral sinusitis. Imaging enabled complete and accurate diagnosis and precise surgical planning. The right-sided fragment was removed through the mouth and the left-sided fragments by a combination of frontal sinoscopy and rostral maxillary sinus trephination. Before the advent of CT, this horse may have been treated by bilateral maxillary flap sinusotomy, but with accurate imaging, a minimally invasive approach is possible. This reduces morbidity and yields an improved cosmetic outcome and faster return to work. Notice the incomplete healing of the alveolar bone plate that resulted from dental sequestration (small arrows) on the transverse section.
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simultaneously if extracted orally, but simultaneous repulsion of more than one tooth should be avoided because the large defect cannot be packed securely. In this instance, the first alveolus should be allowed to heal and fill for approximately 4 to 6 weeks before the second tooth is repulsed.
Sinus Trauma Inherent to the configuration of the equine paranasal sinuses is the risk for fracture from trauma. Often related to a kick or running into an immovable object or fieldmate, depression fractures of the frontal sinus and nasal cavity are common. In these instances it is imperative to avoid general anesthesia in the first 24 to 48 hours so that the neurologic status of the horse can be monitored and treatment provided as required. Computed tomography provides the most complete diagnosis and is recommended in the acute period if it is possible to perform with the horse standing; however, general anesthesia for CT should be avoided. Accurate imaging often allows minimally invasive reconstruction in the standing position under sedation and regional anesthesia. When fractures consist of large interdigitating fragments with intact periosteum, they have intrinsic structural stability when elevated and replaced, even without implants or with only minimal cerclage wire support. This offers substantial advantages over open reduction and internal fixation, which often necessitates general anesthesia with the attendant risks for fracture disruption in recovery. More complex injuries may result in complete loss of periosteal attachments and necessitate removal rather than replacement. Freeform casts can be used for acute external coaptation for transport and for compression to avoid emphysema, as well as in the postoperative period to protect the repair.
Progressive Ethmoidal Hematoma Progressive ethmoidal hematomas (PEHs) are nonneoplastic, progressive, locally destructive masses most commonly originating in the ethmoidal labyrinth. They develop in mature horses and are mostly unilateral, and the purported etiology is trauma with repeated bleeding within the submucosa. The hematomas can enlarge to the point at which they disrupt local architecture and protrude through the various openings within the sinuses (Figure 50-5). They can cause difficult breathing by compression of the nasal cavity, displacement of the turbinates, or directly growing into the nasal cavity. External facial distortion is rare because the masses usually protrude from the nose before this happens. The most common presenting complaint is recurrent, scant, intermittent epistaxis. Other signs may be seen depending on the size and location but may include exercise intolerance or difficult breathing. Diagnosis is usually straightforward, involving radiographic assessment of sinus opacification and recognition of the characteristic greenish brown mass on rhinoscopy. Occasionally, early PEHs may not be readily visible within the ethmoidal labyrinth on endoscopy, but active bleeding can be traced and a presumptive diagnosis made. Computed tomography can be helpful in both early and more advanced cases to determine the full extent of the lesion. In particular, CT increases the margin of safety when treatment with formaldehyde is being considered, because the integrity of the cribriform plate and infraorbital canal can be ascertained before injection, thereby avoiding catastrophic neurologic consequences. Routine conservative treatment of PEH involves direct transendoscopic injection of formalin (4% formaldehyde) through the fibrous submucosal capsule. This can be repeated at 2- to 4-week intervals until the mass is gone. With large
PEH
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Figure 50-5 Large progressive ethmoid hematoma originating in the ethmoid labyrinth, protruding into the nasopharynx, and partially obstructing the nasal cavity. The base of this mass was accessed sinoscopically through a frontal trephine and a window in the medial wall of the dorsal conchal sinus. The mass was injected with formalin and resected 24 hours later under rhinoscopic and sinoscopic guidance.
masses that occlude the nasal cavity, a sinoscopic approach can be made to the base of the lesion and formalin injected there, followed 24 hours later by maceration and suction of the hemorrhagic internal contents and finally removal of the outer sac (see Figure 50-5). The mass must be injected with formalin until it swells and some backleaking of fluid occurs around the injection needle. Excessive leakage of formalin into the surrounding sinus cavity must be avoided, and thorough lavage of any leaked fluid is essential. Hematomas can also be resected surgically or by use of transendoscopic laser ablation, and it is recommended that this be performed in the standing patient to minimize hemorrhage. It is wise to have a cross-matched or universal donor available when resecting a mass with its base in the ethmoid labyrinth, particularly when resection is through bone flap osteotomy under general anesthesia. Reported recurrence rates after surgical resection are as high as 44%, and debulking can be followed up with local formalin treatment of any regrowth.
Sinus Cysts Sinus cysts are expansile, fluid-filled, space-occupying lesions that often cause distortion of the external and internal bony anatomy of the paranasal sinuses. The etiology of this condition remains unclear, and it has been described in horses of all ages, from neonates to mature horses. With the advent of complete imaging studies of the sinuses, sinus cysts are being identified more commonly as a secondary lesion alongside other conditions such as dental disease, suggesting a possible traumatic or inflammatory etiology. Fluid accumulation secondary to cyst distortion of internal anatomy often results in mucoid or mucopurulent nasal discharge. The radiographic finding of a rounded soft tissue opacity within the sinuses, occasionally with dystrophic mineralization evident in the lining, is strongly suggestive of a sinus cyst. Computed tomography can confirm a soft tissue opacification, and comparison of Hounsfield units with surrounding soft tissues, as
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X
Figure 50-6 Suture periostitis. Transverse (A) and three-dimensional reconstruction (B) of the horse in Figure 50-5, 6 weeks after right-sided surgery for PEH. Notice the circular defect of the previous frontal trephine (X) lying directly on the frontonasal suture line. Two weeks after surgery, the horse developed a dramatic soft tissue and bony reaction over the bridge of the nose between the eyes and around the left eye, and also had some discomfort when eating. The horse was treated with phenylbutazone for 6 weeks, after which the swelling and pain resolved almost completely. The temptation to intervene surgically in such cases should be resisted as long as a septic process can be ruled out. Completely avoiding the suture line when placing an osteotomy is impossible in many instances, but smaller osteotomies make this easier.
X
A well as the uniform appearance of the internal architecture of the mass, suggests a cyst. Sinocentesis yields a strawcolored proteinaceous fluid. Definitive treatment is surgical resection, and depending on surgeon preference, lesion size and location, and sensitivity of available imaging techniques, this can be completed through a combination of frontal and maxillary sinoscopy portals or flap osteotomies. Ideally, the lining must be removed to minimize the likelihood of recurrence, but this can be particularly difficult in cases with extension into the sphenopalatine sinuses.
Neoplasia Despite advances in imaging, earlier recognition of suggestive clinical signs, and advances in treatment options, neoplasia remains one of the most intractable conditions of the equine nasal cavity and paranasal sinuses. Although neo plasia of the paranasal sinuses is rare, squamous cell carci noma is the most commonly diagnosed type, with spindle cell sarcoma, mastocytoma, hemangiosarcoma, angiosarcoma, lymphosarcoma, osteoma, osteochondroma, fibroma, and fibrosarcoma all reported. Clinical signs are nonspecific and vague, similar to those of other, less urgent conditions, often resulting in delayed presentation and slow definitive diagnosis. An accurate diagnosis is best achieved through endoscopy, careful imaging, and biopsy by a trephine approach as described for sinoscopy. It is imperative that a representative tissue sample be obtained from the body of the mass, rather than simply a sample of overlying thickened, reactive sinus mucosa. Benign lesions, such as some tumors of bone and dental origin, can be resected with the trephine or osteoplastic flap approaches with reasonable prognoses, but more aggressive lesions, such as carcinomas and sarcomas, can only be treated palliatively, and there is often rapid progression to intolerable clinical signs such as exophthalmos and persistent epistaxis.
Frontal Exostosis Frontonasal exostosis or suture periostitis refers to the hard, painless, or occasionally painful swellings overlying the suture lines between the frontal and nasal bones, or the nasal and lacrimal bones (see Color Plate 50-2). These swellings
B can arise spontaneously or as a result of trauma to the suture lines, including surgical approaches that breech them, such as frontonasal sinusotomy flaps or large frontal trephines (Figure 50-6). When spontaneous, the etiology of these swellings is unknown. Computed tomography has demonstrated marked periosteal and endosteal reactions with apparent fragmentation and lysis of the surrounding bone. In postsurgical cases, septic processes must be ruled out, but in the absence of identifiable bone infection or sequestration, the temptation to intervene surgically should be resisted. When evident, pain and soft tissue swelling decline rapidly within weeks with judicious use of antiinflammatories. In contrast, surgical intervention may superimpose infection on an aseptic process and compound the condition. The firm swelling may resolve rapidly, slowly over the course of several years, or may remain.
Suggested Readings Perkins JD, Bennett C, Windley Z, et al. Comparison of sinoscopic techniques for examining the rostral maxillary and ventral conchal sinuses of horses. Vet Surg 2009;38:607-612. Perkins JD, Windley Z, Dixon PM, et al. Sinoscopic treatment of rostral maxillary and ventral conchal sinusitis in 60 horses. Vet Surg 2009;38:613-619. Schumacher J, Crossland LE. Removal of inspissated purulent exudate from the ventral conchal sinus of three standing horses. J Am Vet Med Assoc 1994;205:1312-1314. Schumacher J, Dutton DM, Murphy DJ, et al. Paranasal sinus surgery through a frontonasal flap in sedated, standing horses. Vet Surg 2000;29:173-177. Schumacher J, Honnas C, Smith B. Paranasal sinusitis complicated by inspissated exudate in the ventral conchal sinus. Vet Surg 1987;16:373-377. Schumacher J, Moll HD, Schumacher J, et al. A simple method to remove an epidermal inclusion cyst from the false nostril of horses. Equine Pract 1997;19:11-13. Tremaine WH, Clarke CJ, Dixon PM. Histopathological findings in equine sinonasal disorders. Equine Vet J 1999;31: 296-303. Witte TH, Perkins JD. Early diagnosis may hold the key to the successful treatment of nasal and paranasal sinus neoplasia in the horse. Equine Vet Educ 2011;23:441-447.
C H A P T E R
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THOMAS H. WITTE
CLINICALLY RELEVANT ANATOMY AND PHYSIOLOGY
The rostral extent of the nasal cavities, the external nares, is supported by cartilage and muscle. This makes them mobile and flexible, allowing for sealing of the nasal cavity during swimming and widening at maximal exercise, but also allowing for pathologic collapse when there is neuromuscular dysfunction. The clinically significant landmarks of this region include the nasolacrimal ostium at the ventral aspect at the mucocutaneous junction, which is easily cannulated there, and the nasal diverticula, or false nostrils. These blindending, hair-lined pockets are closely associated with the lateral aspect of the external nares, from which they are separated by the alar cartilages. Continuing caudally, the midline cartilaginous nasal septum divides the nasal cavity into left and right halves. These cavities are further subdivided by the dorsal and ventral turbinates into the dorsal, middle, ventral, and common meatus (Figure 50-1). The turbinates are scrolled bones that project into the nasal cavity from the lateral wall. The internal space within each scroll is divided into rostral and caudal cavities. The rostral components are termed recesses and are less clinically significant than the caudal components, which form the dorsal and ventral conchal sinuses and communicate with the frontal and rostral maxillary sinuses, respectively. The submucosa of the nasal cavity is highly vascular, in keeping with the function of warming and humidifying inspired air. Because the nasal cavity is encased in rigid bone, any space-occupying lesion here will have a marked impact on airflow and hence athletic performance. Simple vascular congestion caused by iatrogenic jugular thrombophlebitis or loss of sympathetic tone in Horner’s syndrome can be performance limiting and, if left undetected, will limit the success of other upper respiratory tract interventions. The caudal extent of the nasal cavity is bounded dorsally by the middle turbinate, which is surrounded on its caudal aspect by the fine, highly vascular cartilaginous ethmoturbinate scrolls, collectively termed the ethmoidal labyrinth. The increased surface area provided by the labyrinth is lined with olfactory epithelium and with sensory neurons whose axons converge to form the olfactory nerve (cranial nerve [CN] I). Although the integrity of the cribriform plate caudal to the ethmoid is crucial when considering treatment options in this area, it cannot be examined endoscopically in the normal horse. The paranasal sinuses lie lateral and dorsal to the nasal cavity, and although they are made up of six paired chambers, they can be considered as two functional compartments: rostral and caudal. The two compartments drain separately to the middle meatus through the rostral and caudal maxillary sinuses and a common aperture. The nasomaxillary aperture cannot be seen directly with standard endoscopic techniques and equipment, and under normal
circumstances, the paranasal sinuses cannot be accessed directly through the nose. Endoscopic evidence of sinus disease is therefore often limited to fluid egress at the drainage angle of dorsal and ventral turbinates in the dorsal nasopharynx, rostral to the middle turbinate. The caudal paranasal compartment consists of frontal, dorsal conchal, caudal maxillary, and sphenopalatine sinuses. The rostral compartment, which is separated from the caudal compartment by the oblique, curved maxillary septum and its dorsal continuation as the bulla of the ventral conchal sinus, consists of rostral maxillary and ventral conchal sinuses. The rostral maxillary and ventral conchal sinuses communicate over the infraorbital canal and are separated ventrally by the septum that supports this structure, or the maxillary cheek teeth, depending on the age of the horse (see Figure 50-1). The caudal outpouching of the ventral conchal sinus is known as the bulla of the ventral conchal sinus and represents a key surgical landmark. The channel for drainage from both the caudal and rostral sinus compartments into the middle meatus is closely associated with this structure. The conjoined sphenoidal and palatine sinuses (known as the sphenopalatine sinus) extend under the ethmoid and the base of the skull (see Color Plate 50-1). Any space-occupying lesion in this area can cause compression of the optic nerves, brain, and pituitary gland, resulting in unusual presenting complaints. Health of the paranasal sinuses in any species relies on adequate ventilation through the natural ostia and on mucociliary transport provided by ciliated columnar epithelium. The mucociliary escalator works toward the natural drainage channels from the rostral and caudal maxillary sinuses, maintaining a continuous protective mucus layer flowing out of the sinuses. This flow is aided by gravity when the head is down, but continues against gravity at other times. The narrow drainage channels are easily obstructed and distorted by primary disease processes, and the resultant impaired drainage must be recognized and addressed. Surgical interventions should be planned carefully with the goal of maintaining or restoring normal mucociliary clearance from the dependent sinuses, rather than creating new drainage ostia in a separate location. Termed functional sinus surgery in humans, this approach aims to be mucosa sparing when possible. The evolution of endoscopic techniques has contributed to the revolution in surgery of the paranasal sinuses. The relationship between the cheek teeth and the paranasal sinuses is clinically significant. Part of the upper Triadan 08 tooth and the entire root system of the 09 are usually associated with the floor of the rostral maxillary sinus, whereas the roots of the 10 and 11 are associated with the floor of the caudal maxillary sinus (see Color Plate 50-1). Periapical disease of these teeth commonly results in secondary sinusitis, compared with periapical disease of the more
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FS DCS MM VCS RMS
110
The nares should be dry and free from crusting, except for a small volume of tears evident at the nasolacrimal ostium. Airflow should be tested at the external nares; subtle differences may be more obvious after temporary occlusion of airflow or by the use of strands of cotton to detect airflow. Horses with restricted airflow at any level of the respiratory tract may dilate their nostrils bilaterally. The nostrils should remain mobile and tactile and respond to internal and external palpation. Deformation of the facial contour over the paranasal sinuses indicates pressure buildup within the sinuses and most commonly points to a space-occupying lesion such as a cyst or neoplasia. Severe secondary sinusitis cannot, however, be ruled out as a cause of facial distortion because complete occlusion of drainage can result in sufficient pressure to cause distortion. Although percussion of the sinuses for fluid- or soft tissue–induced dullness and palpation of the lymph nodes should form part of any routine physical examination of the head, the findings are often equivocal and difficult to interpret definitively.
Endoscopy
Figure 50-1 Transverse computed tomogram of the nasal cavity and paranasal sinuses at the level of tooth 110. FS and DCS, frontal and dorsal conchal sinuses, respectively, often referred to as the combined conchofrontal sinus; MM, middle meatus; RMS, rostral maxillary sinus; VCS, ventral conchal sinus. Curved arrow indicates drainage channel from the rostral maxillary sinus; notice the relationship to the ventral turbinate and floor of the frontal sinus. A circle of bone encompasses the infraorbital canal; notice its relationship to the RMS, VCS, and maxillary cheek teeth.
rostral teeth (06 to 08), in which facial swelling or external draining tracts are more common. The proximity of the teeth makes trephination of the maxillary sinuses difficult and often unrewarding, particularly in the young horse when the reserve crowns are large and the sinus cavities small. The precise relationship between the apices of the cheek teeth and the respective sinuses cannot be predicted on the basis of plain radiographs: disease of the 08 and 09 teeth can result in sinusitis of the caudal compartment if there is rostral extension of the caudal maxillary sinus and obliquity of the maxillary septum, whereas apical disease of the 10 and 11 teeth can result in sinusitis of the rostral compartments when there is caudal extension of the ventral conchal sinus. Attempting to predict which tooth is infected based on which sinuses are diseased should be avoided.
EXAMINATION
Historical Findings Horses with sinonasal disease can have clinical signs ranging from subtle poor performance, epiphora, or head shaking to the more common nasal discharge, facial swelling, and difficult breathing. Because many horses are not presented until the signs are obvious, disease can be at an advanced stage by the time the horse is first evaluated. Understanding the progression historically can be vital to establishing a valid differential diagnosis list and ensuring that appropriate diagnostic tests are undertaken. In particular, changes in the volume, odor, timing, nature, duration, and laterality of discharge over time can be extremely informative.
Physical Examination The head should be evaluated from both sides and in front for symmetry and swellings as well as for pain on palpation.
Endoscopic examination for nasal and paranasal sinus disease may include rhinoscopy, dentoscopy, and sinoscopy. Rhinoscopy can be performed with a standard flexible endoscope. A videoendoscope allows documentation of findings for serial evaluations and can be particularly helpful in treatment of mass lesions. In the presence of active discharge from the nose, rhinoscopy will confirm the source of the drainage. Routine rhinoscopy should include careful evaluation of the nasopharynx, ethmoidal labyrinth, drainage angle between dorsal and ventral turbinates, and mucosa of the dorsal, ventral, and middle meatus. Dentoscopy or examination of the dental occlusal surfaces with a mirror should be undertaken in any horse with unilateral nasal discharge of unknown etiology and must involve a thorough assessment of the periodontium. Careful documentation of findings enables serial monitoring and helps in client communication. Sinoscopy has become less critical as a diagnostic modality for paranasal sinus disease with the advent and availability of standing computed tomography (CT), although it remains a key tool therapeutically and a cornerstone of the diagnostic process if CT is unavailable. Several approaches to each of the sinus compartments have been described, but the most universal appears to be creation of a frontal sinus portal of an appropriate size to allow a flexible endoscope to be inserted, with or without space to pass an instrument alongside depending on surgeon preference (see Color Plate 50-1). Primary approaches to the maxillary sinuses pose the risk for iatrogenic damage to the cheek teeth and are less useful in gleaning an overview of the global disease state, although they may still be very useful therapeutically when they can be placed under sinoscopic guidance or with the benefit of CT. Sinoscopy is performed in the standing sedated horse, making orientation easier and preventing loss of visibility in the presence of bleeding. Suction should be available if possible. A Galt trephine is used to cut a circular disk of bone from the bone plate. Frequent lavage of the site will prevent the buildup of bone dust subcutaneously and minimize postoperative reaction. A 2.5-cm-diameter trephine appears to be the optimal size because this allows an instrument to be passed alongside the endoscope, avoiding the necessity for a second portal, while not being too large for a good cosmetic outcome. Creating two separate 1-cm trephine holes for the endoscope and instrument is also suitable. The frontonasal suture line should be avoided when possible (see Color Plate 50-2). In general, this suture line runs between the medial
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canthi of the eyes, and placing a trephine or other osteotomy across this line, which becomes more likely with increasing osteotomy size, results in more or less severe suture periostitis. The standard approach to the frontal sinus, caudal to and midway along a line drawn perpendicular to the midline at the level of the medial canthus of the eye, allows the caudal maxillary and conchofrontal sinuses to be explored directly without risk for damage to the intrasinus component of the ethmoid during the approach. Damage to the latter results in profuse hemorrhage, making accurate diagnosis and intervention more difficult. From the frontal sinus, the endoscope can be passed freely through the large frontomaxillary aperture into the caudal maxillary sinus (see Color Plate 50-1). The ventral conchal bulla, the caudal outpouching of the ventral conchal sinus, lies beneath the rostral margin of the frontomaxillary aperture. This cartilaginous bulla, which varies among horses in shape and size and can appear to be absent in horses with chronic deformation of the intrasinus anatomy, can be resected to give access to the rostral maxillary and ventral conchal sinuses. The ventral conchal sinus is often the site of mucus inspissation in cases of chronic sinusitis, and this condition can be confirmed and treated by this approach. When necessary, the frontal portal can be supplemented with a maxillary trephine, which can safely be created under endoscopic guidance and transillumination. Postoperative lavage tubes can be placed through the frontal sinus portal, allowing adequate lavage without creating any further trephines. The pressure of postoperative lavage fluid must be carefully controlled to avoid subcutaneous accumulation of fluid, especially with larger osteotomies.
DIAGNOSTIC IMAGING
Standard lateral and oblique radiographic views of the paranasal sinuses provide a useful baseline, although more specialized views, including intraoral and open-mouth radiographs, are necessary to gain a more complete understanding of the underlying pathology. A dorsoventral view is particularly useful to identify opacification of the ventral conchal sinus or deviation of the nasal septum. Internal dental architecture can also be visualized if the mandibular and maxillary arcades can be offset. Numerous other special projections have been described for imaging the cheek teeth without superimposition and are based on an understanding of the curvature of the dental arcade and the caudal-to-rostral narrowing evident when one carefully examines the equine skull. The ideal projection to isolate the maxillary cheek teeth is thus taken 15 degrees caudal to the straight lateral and 30 degrees dorsal to the horizontal axis. Nuclear scintigraphy can be helpful in determining the clinical significance of a radiographic finding or, more often, can create a suspicion of dental or sinus origin for spurious or vague presenting signs. Lateral and dorsoventral scintigraphic views of the head are easy to acquire and, depending on signalment and history, may form part of any full-body bone scan performed for poor performance. Ultimately, in difficult, refractory, or recurrent cases, referral for CT may be considered necessary, in particular where this modality is available for the standing horse. This technique is considered the gold standard for complete evaluation of intrasinus space-occupying lesions, particularly when neoplasia is suspected, and for the definitive detection of dental pathology. Computed tomography offers advantages in surgical planning, enabling the examiner to identify the relationship between diseased areas and important structures such as the infraorbital nerve, nasolacrimal duct, and cribriform plate. This information allows the application of advanced, minimally invasive, and functional
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endoscopic techniques for the treatment of the full range of sinus diseases.
DISEASES OF THE NASAL CAVITY Epidermal Inclusion Cysts
The term atheroma is sometimes inappropriately used to describe the variably sized soft, fluctuant swellings found within the nasal diverticulum in horses around the age of 2 years. These swellings are epidermal inclusion cysts that enlarge continuously from exfoliation of squamous cells from their lining. Most commonly these lesions do not threaten the lumen of the airway because they bulge laterally, and their significance is rarely anything more than cosmetic. Diagnosis is based on the pathognomonic location and gross appearance of the lesion, and aspiration yields a gray, odorless, greasy fluid. The masses can be removed intact through an external skin incision, and injection of formalin has been reported, but the most predictable cosmetic outcome is achieved by incising and removing the cyst lining with a ventriculectomy burr placed through the external nares.
Alar Fold Collapse Alar fold collapse causes an abnormal upper respiratory tract noise that must be differentiated from laryngeal and pharyngeal dysfunction. The noise may be heard at rest or may only be elicited by intense exercise, and has variously been described as a muffled rattling or vibrating noise heard during both inspiration and expiration. Horses may be presented for evaluation primarily because of the noise or because of poor performance. Dynamic respiratory endoscopy can be useful in ruling out other causes of abnormal upper respiratory tract noise and poor performance, but definitive diagnosis necessitates temporary retraction of the alar folds with sutures. By use of a twitch and local anesthesia, suture material is placed through each alar fold and tied dorsally over the nasal bones, occluding the nasal diverticula. Absence of noise after suture placement and recurrence with suture removal provides a definitive diagnosis and justifies surgical resection of the alar folds. Surgery can be performed with the horse anesthetized and positioned in dorsal or lateral recumbency, or with the horse standing. The procedure can be performed through an intact nostril, but some surgeons prefer to incise the lateral alae of the nostrils to expose the alar folds more completely and to ensure complete resection of all associated tissue.
Wounds of the External Nares When left to heal by second intention, wounds of the external nares can deform the contour, flexibility, and function of the nostril. To preserve function and cosmesis, careful reconstruction can be undertaken with a three-layer closure after debridement, when necessary. Only rarely, in the presence of severe contamination or maceration of tissue, must such injuries be left to heal by second intention or, preferably, be closed with delayed primary closure.
Lateral Deviation of the Nose Congenital lateral deviation of the nose, so-called wry nose, has an unknown etiology. Intrauterine factors have been purported to contribute, and a genetic predisposition seems likely, with Arab horses overrepresented. Commonly affecting the maxillary, nasal, and incisive bones and the nasal septum, the deviation has a profound effect on respiration. The effect on the foal’s ability to suckle is less predictable, but when suckling is affected, a concomitant cleft palate must be ruled out. Surgical correction of wry nose through
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multiple osteotomies is a technical challenge but can in rare cases result in an athletic career. Preservation of such animals as breeding stock should be questioned, but they may be suitable for pleasure riding.
Imperforate Buccopharyngeal Septum An imperforate buccopharyngeal septum, also known as choanal atresia, can result in a range of clinical signs, from apparent stillbirth in foals to abnormal respiratory noise during exercise in adults. The buccopharyngeal septum separates the nasal cavity from the nasopharynx in the developing embryo, and its remnant may be unilateral or bilateral, complete or incomplete, and membranous or bony, which explains the diversity of clinical signs. In the neonate, inspiratory stridor and bulging of the guttural pouches may be evident, and temporary tracheostomy may be required to stabilize the patient. Inability to advance a nasogastric tube beyond the nasal passage may alert the clinician to the airway obstruction, and definitive diagnosis is achieved endoscopically or by contrast radiography. Resection has been attempted through a variety of approaches, from endoscope-guided approaches through the nose for membranous obstructions to facial bone osteotomies for bony obstructions. The latter must be performed with caution in the growing animal because growth will almost certainly be impaired after interference with the suture lines, and deformity will result. Maintaining patency after fenestration presents one of the largest challenges, and repeated procedures are necessary in many cases.
Mycotic Rhinitis Infection of the nasal and paranasal mucosa by normally saprophytic fungi such as Aspergillus fumigatus and Pseudallescheria boydii commonly occurs secondary to previous damage such as traumatic injury or surgery. However, cases in which a primary underlying cause cannot be identified are not unusual. Stabled horses that are exposed to moldy hay and straw are likely to be predisposed to mycotic rhinitis. Typical presenting signs include unilateral malodorous mucopurulent nasal discharge. Intermittent mild epistaxis is occasionally seen. Definitive diagnosis is usually straightforward, based on the characteristic appearance of the plaques; however, cytologic examination and fungal culture of the plaques are still recommended, and these appear to yield superior results to those obtained with collection and culture of the exudate. Treatment involves resolution of primary disease, removal of fungal plaques, and topical application of antifungals. Drugs effective against Aspergillus spp include itraconazole, fluconazole, enilconazole, miconazole, ketoconazole, natamycin, clotrimazole, and amphotericin. These may be administered in powder or liquid form, although availability may vary. Administration of the powder form of medication offers advantages with regard to duration of contact, but application can be more challenging.
DISEASES OF THE PARANASAL SINUSES
Diseases of the paranasal sinuses can be thought of as primary infections, secondary infections, and space-occupying lesions, with overlap existing between the categories.
Infectious Sinusitis Primary infections of the sinus commonly follow more generalized infections of the upper respiratory tract. The most common bacterial isolates are members of the streptococcal family, particularly Streptococcus equi subsp equi and zooepidemicus. Primary sinusitis can affect any age group and
generally involves all sinus cavities. If treated promptly and effectively, the medium- to long-term consequences are negligible; however, if the process becomes chronic with mucus inspissation in the ventral conchal sinus, the condition may only be successfully treated by surgery. The diagnosis of primary sinusitis is often made presumptively after endoscopic confirmation of the sinus as the source of an active nasal discharge. Horizontal fluid lines within the sinuses on lateral and oblique radiographs can help further localize the disease process. In the worst cases, with long-standing disease and inadequate drainage, opacification may be extensive, making differentiation from space-occupying lesions difficult. Sinocentesis may be helpful and can be combined with sinus lavage (see Color Plate 50-2). Simple sinocentesis can be performed with a 14-gauge needle tapped through the bone with a mallet, or a dog urinary catheter may be inserted through a hole created with a small Steinmann pin and Jacob’s chuck. The results of cytologic examination and culture may aid in ruling out underlying pathology. Culture of a single bacterial species indicates that the sinusitis is most likely caused by primary bacterial infection. When multiple bacteria are identified or plant material is seen macroscopically or microscopically, periapical dental infection or an orosinus fistula should be suspected. In acute cases of primary sinusitis, empirical treatment with broad-spectrum antimicrobials and antiinflammatories may be effective alone or in combination with simple sinus lavage. During lavage, the clinician should assess the patency of the drainage channel and thereby the likelihood of response to conservative management. After treatment, it may be unclear whether the disease has resolved or the clinical signs have merely been suppressed. Recurrence of signs should prompt further investigation for an underlying primary cause or inspissation. In more chronic cases in which fluid is inspissated or drainage has been impaired, sinoscopy should be performed through a frontal sinus portal as described to remove inspissated material and enlarge the drainage channel if necessary (Figure 50-2). The author routinely resects the bulla of the ventral conchal sinus in all cases to allow direct lavage of both caudal and rostral spaces from a single frontal portal postoperatively. This also allows access to inspissated material in the ventral conchal sinus. Resection of the bulla will enhance drainage to the middle meatus, and in cases in which drainage is severely impaired, dissection can be continued medially and ventrally to remove the dorsal margin of the free wall of the ventral turbinate and enlarge the ostium. In line with a mucosa-sparing functional approach, this is preferred to the creation of artificial drainage at a separate location, such as ventrally within the ventral conchal sinus. The latter approach is more traumatic, is more likely to result in excessive scar tissue, and does not reestablish mucociliary clearance through the normal apertures. It is also more difficult to perform in the standing horse without inducing substantial hemorrhage and the need for postoperative tamponade. Even in chronic cases with severe distortion, enlargement of natural drainage is possible and preferred.
Chronic Sinusitis The most common cause of secondary infections of the sinuses is dental disease, with one half of all sinusitis cases originating from apical infections of the maxillary cheek teeth, diastemata with severe periodontal disease, idiopathic dental fractures, and displaced or supernumerary cheek teeth (Figure 50-3).
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SPS CMS
RMS VCS VCS
108
A
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Figure 50-2 Inspissated material in the ventral conchal sinus (VCS), associated with pulpitis and periapical disease of tooth 108. Notice the presence of gas (black) within the pulp chambers of 108 (A), indicative of pulpitis, and widening of the alveolar space, indicative of periapical disease. Although the primary disease process is in the rostral compartment, opacification of the caudal maxillary (CMS) and sphenopalatine (SPS) sinuses can be seen resulting from occlusion of drainage from the caudal compartments secondary to distortion of drainage anatomy around the bulla of the ventral conchal sinus. The nature of the fluid was anticipated from CT findings and was confirmed on sinoscopic evaluation. The VCS was filled with inspissated material and the CMS and SPS with nonseptic sinus fluid. This case highlights the importance of reestablishing drainage from all sinus compartments, particularly when the internal architecture is distorted.
B
Horses with sinusitis originating from periapical infection of the cheek teeth often have a protracted history of uni lateral nasal discharge. Some response to antimicrobial administration may be seen, but malodorous mucopurulent unilateral nasal discharge returns when treatment is discontinued. A foul odor is a common feature of this condition, but is by no means pathognomonic for periapical tooth infection because it can occur with any disease process in which tissue necrosis is a feature. The caudal cheek teeth (08 to 11) are most often implicated in sinusitis, whereas apical disease of the rostral teeth (06 to 08) most commonly results in facial swelling or draining tracts. This general rule is not fail-safe, however, and presenting signs will depend on the rostral-caudal extension of the individual sinus compartments. Extension of periapical disease and hence drainage directly into the nasal cavity is also possible. Rhinoscopic findings do not help differentiate primary from secondary sinusitis. An oral cavity examination should be completed in all cases of sinusitis that do not respond to initial conservative management. However, the presence or absence of occlusal surface findings does not always confirm or rule out a dental etiology. Extreme care must therefore be taken to ensure that radical and irreversible treatments such as dental extraction are only undertaken when a tooth can be definitively identified as the cause of sinus disease. Radiographs can provide additional clues, in particular periapical osteolysis surrounded by a zone of sclerosis, blunting of tooth roots, and loss of definition of the lamina dura denta, but radiographic changes are notoriously insensitive. A variety of oblique, open-mouth, and intraoral views can be used to image the internal architecture of the teeth and help reach a more definitive diagnosis. Scintigraphy is more sen sitive for identifying an active process but has also been superseded by CT. Computed tomography is now routinely performed in the sedated, standing horse, enabling the entire process of diagnosis and treatment to be completed without the need for general anesthesia. Computed tomography allows assessment of periapical changes to the lamina dura denta and surrounding bone, as well as abnormalities of the internal anatomy of the tooth, such as pulpitis with gas accumulation, widening of the pulp chambers, irregularity
S 211 210 209 208 207 206
Figure 50-3 Developmental dental abnormalities: a supernumerary tooth (S) is visible at position 212. Small arrows delineate periodontal pocketing of feed material and opacification of the associated caudal and rostral maxillary sinuses (compare with normal right side). In this instance, removal of the tooth was necessary to resolve sinusitis and periodontal disease, but this is not always the case. Such supplemental teeth, which resemble normal teeth, must be differentiated from connate teeth, in which the tooth is composed of multiple tooth elements arising from a single alveolus. The latter are more difficult to extract and may not need extraction. Computed tomography helps to clearly define the disease process and to establish a clear dental origin for the presenting signs before extraction is considered.
of the walls of the chambers, and enamel breech between infundibulum and pulp in the case of extensive infundibular caries or cemental hypoplasia (see Figure 50-2). Resolution of sinusitis relies on definitive identification and treatment of all underlying pathology. In the case of
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dental sinusitis, current best practice in the absence of good evidence for dental preservation of infected cheek teeth is dental extraction. Oral extraction techniques enable this to be completed in the standing patient without recourse to approaches through the sinus. Wide sinus exposures, such as flap osteotomies or large trephine holes, are no longer considered necessary for dental extraction, except in very rare cases of extreme displacement and in intractable patients who do not allow work in the standing position through the mouth. One of the most important advantages of oral extraction is retention of an intact alveolar bone plate, negating the need for a watertight seal of the alveolus, as would be the case after tooth repulsion when there is a real risk for orosinus fistula formation. After oral extraction, the alveolus should be packed with gauze dressing impregnated with a dilute povidone-iodine solution for the first few days. The goal is to retain the initial alveolar hematoma within the socket and to protect the socket during the initial inflammatory phase of healing. Packing is not required beyond the first 5 days. Granulation of the alveolus can be promoted by applying very strong iodine or other irritant agents to the socket; however, this is considered unnecessary and may even promote sequestration of the alveolar wall. In nonsinusitis cases, fracture of the tooth during extraction may not necessitate complete fragment retrieval, but in cases with more extensive and apical pathology and in those with sinusitis, dental remnants are often sufficient to incite ongoing clinical signs and must be retrieved (Figure 50-4). A variety of oral and minimally invasive approaches exist to achieve this, including mini-buccotomy with screw extraction and mini-trephine and repulsion with a Steinmann pin, both of which can be performed in a standing sedated horse. Alongside dental extraction, the sinuses most often require lavage,
and this can most easily be achieved through a sinoscopic approach as described earlier. This helps to confirm the diagnosis of dental pathology and allows adequate drainage to be ensured. It is performed before dental extraction in the same sedative episode in most cases. Systemic antimicrobials and antiinflammatories should be used in the first 5 days after extraction, particularly in more involved cases in which surgical trauma is substantial. Orosinus fistulae are a substantial risk after dental repulsion, in contrast to oral extraction, in which the alveolar bone plate remains intact. Sequestration of the alveolar wall or dental remnants can result in delayed healing, or the dental plug may be lost prematurely before the alveolus has healed, resulting in contamination of the sinus with feed material. The hallmark clinical signs are sudden recurrence of severe nasal discharge, often with feed material evident at the external nares. Management should be directed at achieving an accurate and complete diagnosis of the underlying pathology. Sequestration of bone or tooth must be ruled out. When available, CT provides a more complete understanding of the causes of fistula formation and enables more definitive treatment, often using minimally invasive approaches (see Figure 50-4). In the absence of such a complete diagnosis, an empirical approach is to perform maxillary flap sinusotomy to provide wide exposure to the affected alveolus for sequestrectomy and debridement. The socket is packed with dental impression material or equivalent from the oral side to create a seal. Thorough lavage and confirmation of adequate drainage from an often severely inflamed sinus are also critical. If conservative approaches fail or in the case of large mature defects, muscle transposition can be performed by a variety of approaches. The risk for fistulation is increased if two adjacent teeth require extraction. The teeth can be removed
CMS VCS RMS RMS
Figure 50-4 A single large and multiple small tooth fragments (large arrows) within the 109 and 209 alveoli, respectively. The fragments were left after the teeth were incompletely extracted through the oral cavity, and led to chronic bilateral sinusitis. Imaging enabled complete and accurate diagnosis and precise surgical planning. The right-sided fragment was removed through the mouth and the left-sided fragments by a combination of frontal sinoscopy and rostral maxillary sinus trephination. Before the advent of CT, this horse may have been treated by bilateral maxillary flap sinusotomy, but with accurate imaging, a minimally invasive approach is possible. This reduces morbidity and yields an improved cosmetic outcome and faster return to work. Notice the incomplete healing of the alveolar bone plate that resulted from dental sequestration (small arrows) on the transverse section.
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50 Diseases of the Nasal Cavity and Paranasal Sinuses
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simultaneously if extracted orally, but simultaneous repulsion of more than one tooth should be avoided because the large defect cannot be packed securely. In this instance, the first alveolus should be allowed to heal and fill for approximately 4 to 6 weeks before the second tooth is repulsed.
Sinus Trauma Inherent to the configuration of the equine paranasal sinuses is the risk for fracture from trauma. Often related to a kick or running into an immovable object or fieldmate, depression fractures of the frontal sinus and nasal cavity are common. In these instances it is imperative to avoid general anesthesia in the first 24 to 48 hours so that the neurologic status of the horse can be monitored and treatment provided as required. Computed tomography provides the most complete diagnosis and is recommended in the acute period if it is possible to perform with the horse standing; however, general anesthesia for CT should be avoided. Accurate imaging often allows minimally invasive reconstruction in the standing position under sedation and regional anesthesia. When fractures consist of large interdigitating fragments with intact periosteum, they have intrinsic structural stability when elevated and replaced, even without implants or with only minimal cerclage wire support. This offers substantial advantages over open reduction and internal fixation, which often necessitates general anesthesia with the attendant risks for fracture disruption in recovery. More complex injuries may result in complete loss of periosteal attachments and necessitate removal rather than replacement. Freeform casts can be used for acute external coaptation for transport and for compression to avoid emphysema, as well as in the postoperative period to protect the repair.
Progressive Ethmoidal Hematoma Progressive ethmoidal hematomas (PEHs) are nonneoplastic, progressive, locally destructive masses most commonly originating in the ethmoidal labyrinth. They develop in mature horses and are mostly unilateral, and the purported etiology is trauma with repeated bleeding within the submucosa. The hematomas can enlarge to the point at which they disrupt local architecture and protrude through the various openings within the sinuses (Figure 50-5). They can cause difficult breathing by compression of the nasal cavity, displacement of the turbinates, or directly growing into the nasal cavity. External facial distortion is rare because the masses usually protrude from the nose before this happens. The most common presenting complaint is recurrent, scant, intermittent epistaxis. Other signs may be seen depending on the size and location but may include exercise intolerance or difficult breathing. Diagnosis is usually straightforward, involving radiographic assessment of sinus opacification and recognition of the characteristic greenish brown mass on rhinoscopy. Occasionally, early PEHs may not be readily visible within the ethmoidal labyrinth on endoscopy, but active bleeding can be traced and a presumptive diagnosis made. Computed tomography can be helpful in both early and more advanced cases to determine the full extent of the lesion. In particular, CT increases the margin of safety when treatment with formaldehyde is being considered, because the integrity of the cribriform plate and infraorbital canal can be ascertained before injection, thereby avoiding catastrophic neurologic consequences. Routine conservative treatment of PEH involves direct transendoscopic injection of formalin (4% formaldehyde) through the fibrous submucosal capsule. This can be repeated at 2- to 4-week intervals until the mass is gone. With large
PEH
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Figure 50-5 Large progressive ethmoid hematoma originating in the ethmoid labyrinth, protruding into the nasopharynx, and partially obstructing the nasal cavity. The base of this mass was accessed sinoscopically through a frontal trephine and a window in the medial wall of the dorsal conchal sinus. The mass was injected with formalin and resected 24 hours later under rhinoscopic and sinoscopic guidance.
masses that occlude the nasal cavity, a sinoscopic approach can be made to the base of the lesion and formalin injected there, followed 24 hours later by maceration and suction of the hemorrhagic internal contents and finally removal of the outer sac (see Figure 50-5). The mass must be injected with formalin until it swells and some backleaking of fluid occurs around the injection needle. Excessive leakage of formalin into the surrounding sinus cavity must be avoided, and thorough lavage of any leaked fluid is essential. Hematomas can also be resected surgically or by use of transendoscopic laser ablation, and it is recommended that this be performed in the standing patient to minimize hemorrhage. It is wise to have a cross-matched or universal donor available when resecting a mass with its base in the ethmoid labyrinth, particularly when resection is through bone flap osteotomy under general anesthesia. Reported recurrence rates after surgical resection are as high as 44%, and debulking can be followed up with local formalin treatment of any regrowth.
Sinus Cysts Sinus cysts are expansile, fluid-filled, space-occupying lesions that often cause distortion of the external and internal bony anatomy of the paranasal sinuses. The etiology of this condition remains unclear, and it has been described in horses of all ages, from neonates to mature horses. With the advent of complete imaging studies of the sinuses, sinus cysts are being identified more commonly as a secondary lesion alongside other conditions such as dental disease, suggesting a possible traumatic or inflammatory etiology. Fluid accumulation secondary to cyst distortion of internal anatomy often results in mucoid or mucopurulent nasal discharge. The radiographic finding of a rounded soft tissue opacity within the sinuses, occasionally with dystrophic mineralization evident in the lining, is strongly suggestive of a sinus cyst. Computed tomography can confirm a soft tissue opacification, and comparison of Hounsfield units with surrounding soft tissues, as
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X
Figure 50-6 Suture periostitis. Transverse (A) and three-dimensional reconstruction (B) of the horse in Figure 50-5, 6 weeks after right-sided surgery for PEH. Notice the circular defect of the previous frontal trephine (X) lying directly on the frontonasal suture line. Two weeks after surgery, the horse developed a dramatic soft tissue and bony reaction over the bridge of the nose between the eyes and around the left eye, and also had some discomfort when eating. The horse was treated with phenylbutazone for 6 weeks, after which the swelling and pain resolved almost completely. The temptation to intervene surgically in such cases should be resisted as long as a septic process can be ruled out. Completely avoiding the suture line when placing an osteotomy is impossible in many instances, but smaller osteotomies make this easier.
X
A well as the uniform appearance of the internal architecture of the mass, suggests a cyst. Sinocentesis yields a strawcolored proteinaceous fluid. Definitive treatment is surgical resection, and depending on surgeon preference, lesion size and location, and sensitivity of available imaging techniques, this can be completed through a combination of frontal and maxillary sinoscopy portals or flap osteotomies. Ideally, the lining must be removed to minimize the likelihood of recurrence, but this can be particularly difficult in cases with extension into the sphenopalatine sinuses.
Neoplasia Despite advances in imaging, earlier recognition of suggestive clinical signs, and advances in treatment options, neoplasia remains one of the most intractable conditions of the equine nasal cavity and paranasal sinuses. Although neo plasia of the paranasal sinuses is rare, squamous cell carci noma is the most commonly diagnosed type, with spindle cell sarcoma, mastocytoma, hemangiosarcoma, angiosarcoma, lymphosarcoma, osteoma, osteochondroma, fibroma, and fibrosarcoma all reported. Clinical signs are nonspecific and vague, similar to those of other, less urgent conditions, often resulting in delayed presentation and slow definitive diagnosis. An accurate diagnosis is best achieved through endoscopy, careful imaging, and biopsy by a trephine approach as described for sinoscopy. It is imperative that a representative tissue sample be obtained from the body of the mass, rather than simply a sample of overlying thickened, reactive sinus mucosa. Benign lesions, such as some tumors of bone and dental origin, can be resected with the trephine or osteoplastic flap approaches with reasonable prognoses, but more aggressive lesions, such as carcinomas and sarcomas, can only be treated palliatively, and there is often rapid progression to intolerable clinical signs such as exophthalmos and persistent epistaxis.
Frontal Exostosis Frontonasal exostosis or suture periostitis refers to the hard, painless, or occasionally painful swellings overlying the suture lines between the frontal and nasal bones, or the nasal and lacrimal bones (see Color Plate 50-2). These swellings
B can arise spontaneously or as a result of trauma to the suture lines, including surgical approaches that breech them, such as frontonasal sinusotomy flaps or large frontal trephines (Figure 50-6). When spontaneous, the etiology of these swellings is unknown. Computed tomography has demonstrated marked periosteal and endosteal reactions with apparent fragmentation and lysis of the surrounding bone. In postsurgical cases, septic processes must be ruled out, but in the absence of identifiable bone infection or sequestration, the temptation to intervene surgically should be resisted. When evident, pain and soft tissue swelling decline rapidly within weeks with judicious use of antiinflammatories. In contrast, surgical intervention may superimpose infection on an aseptic process and compound the condition. The firm swelling may resolve rapidly, slowly over the course of several years, or may remain.
Suggested Readings Perkins JD, Bennett C, Windley Z, et al. Comparison of sinoscopic techniques for examining the rostral maxillary and ventral conchal sinuses of horses. Vet Surg 2009;38:607-612. Perkins JD, Windley Z, Dixon PM, et al. Sinoscopic treatment of rostral maxillary and ventral conchal sinusitis in 60 horses. Vet Surg 2009;38:613-619. Schumacher J, Crossland LE. Removal of inspissated purulent exudate from the ventral conchal sinus of three standing horses. J Am Vet Med Assoc 1994;205:1312-1314. Schumacher J, Dutton DM, Murphy DJ, et al. Paranasal sinus surgery through a frontonasal flap in sedated, standing horses. Vet Surg 2000;29:173-177. Schumacher J, Honnas C, Smith B. Paranasal sinusitis complicated by inspissated exudate in the ventral conchal sinus. Vet Surg 1987;16:373-377. Schumacher J, Moll HD, Schumacher J, et al. A simple method to remove an epidermal inclusion cyst from the false nostril of horses. Equine Pract 1997;19:11-13. Tremaine WH, Clarke CJ, Dixon PM. Histopathological findings in equine sinonasal disorders. Equine Vet J 1999;31: 296-303. Witte TH, Perkins JD. Early diagnosis may hold the key to the successful treatment of nasal and paranasal sinus neoplasia in the horse. Equine Vet Educ 2011;23:441-447.