Sinoscopy in the standing horse
Sinoscopy is a minimally invasive diagnostic procedure that can be performed on the standing horse. The technique can allow good visualization and treatment of paranasal sinus disease and eliminate the need for more invasive procedures such as large bone flaps. Knowledge of the anatomy of the paranasal sinuses is the most important aspect of the procedure.
Paranasal sinus disorders include primary or secondary sinusitis, progressive ethmoid hematoma, sinus cysts and, more rarely, neoplasia. Due to the size and complex anatomy, these pathological processes can sometimes be present for weeks or months before clinical signs such as a runny nose or swelling of the face are evident.1 Treating chronic equine paranasal sinus disorders can be frustrating, but the long-term prognosis is usually excellent unless the diagnosis is neoplasia.2
Imaging of the paranasal sinuses is essential for diagnosis and surgical planning in affected horses. Radiography and computed tomography (CT) are the most commonly used. Sinoscopy is a simple and minimally invasive procedure compared to traditional paranasal sinus surgical approaches, potentially reducing the incidence of complications. It also provides a way to more accurately diagnose, and subsequently treat, certain underlying conditions. Sinoscopy has been reported as the most useful diagnostic tool compared to radiography and endoscopy in horses with sinus pathology. It allowed an exact diagnosis in 70% of patients, against endoscopy in 20% and radiography in 36%. Changes including thickening or inflammation of the sinus lining, lesions occupying space, exudate, associated dental abscesses, and fungal lesions can be diagnosed using this modality.1
The horse has 6 paired paranasal sinuses (frontal, rostral maxilla, caudal maxilla, sphenopalatine and the dorsal and ventral conch sinuses) which communicate with each other and with the nasal passage directly or indirectly. The frontal sinus and the maxillary caudal sinus communicate by the frontomaxillary orifice; the sphenopalatine and the caudal maxillary sinus communicate through the sphenopalatine orifice; and the rostral maxilla and ventral conch sinus communicate via the conchomaxillary opening. A thorough understanding of spatial structural relationships is crucial for successful surgery in the region.3
Sinoscopy can be performed under standing sedation using a sterile flexible arthroscope or fiberscope or a video endoscope via a conchofrontal or rostral maxillary trephine opening. The trepanation site is prepared for surgery and desensitized by subcutaneous injection of local anesthetics. Sinoscopy gates are made in the frontal or maxillary bone after skin incisions, using a 9.5 mm to 15 mm Galt trephine. Initial irrigation or aspiration may be necessary to improve visualization if the sinus compartments are filled with exudate. The skin incision is closed with staples or skin sutures after the sinoscopy is complete.
Sinus compartments that can be visualized directly through a conchofrontal trephine portal include the frontal, caudal maxilla, and dorsal conch sinuses. The ethmoid turbinates, the frontomaxillary opening and the nasomaxillary opening are also visible. Structures observed in the maxillary caudal sinus include the infraorbital canal, the apices of the 10th and 11th maxillary jaw teeth, the maxillary septum, and the entrance to the sphenopalatine sinus.4 The same structures can be seen through an opening of the maxillary rostral trephine, but the entrance to the sphenopalatine sinus may not be accessible.
The maxillary rostral sinus and the ventral conch sinus are frequent sites of infection caused by apical dental infection or inspected exudate, respectively. However, these sinuses are not directly accessible from the trephine holes in the conchofrontal or caudal maxillary sinuses (Figure 1). The maxillary rostral sinus can be examined independently by a maxillary bone trepanation placed rostrally. However, this is generally not recommended in young horses to avoid iatrogenic damage to the reserve crowns of the ninth and tenth maxillary teeth. The ventral conch sinus and the rostral maxillary sinus can both be assessed by a gate in the conchofrontal or caudal maxillary sinuses after fenestration of the maxillary cartilaginous septal bulla (formerly called ventral conch bulla). The maxillary septal bulla is desensitized with topical local anesthetics and fenestrated with endoscopic guidance using a Ferris-Smith arthroscopic gouge forceps, alligator clip or diode laser through the same gate as the endoscope (Figure 2). If the fenestration of the bubble causes bleeding that interferes with observation, the sinuscopy should be repeated after 24 to 48 hours. It is possible to wash all the compartments after windowing the bubble.4
- Tremaine WH, Dixon PM. A long-term study of 277 cases of equine nasosinus disease. Part 1: details of horses, historical, clinical and auxiliary diagnostic results. Equine Vet J. 2001; 33 (3): 274-282. doi: 10.2746 / 042516401776249615
- Dixon PM, Parkin TD, Collins N, et al. Equine paranasal sinus disease: a long-term study of 200 cases (1997-2009): treatments and long-term treatment outcomes. Equine Vet J. 2012; 44 (3): 272-276. doi: 10.1111 / j.2042-3306.2011.00427.x
- Tatarniuk DM, Bell C, Carmalt JL. A description of the relationship between the nasomaxillary opening and the paranasal sinus system of horses. Veterinarian J. 2010; 186 (2): 216-220. doi: 10.1016 / j.tvjl.2009.07.023
- Perkins JD, Windley Z, Dixon PM, Smith M, Barakzai SZ. Sinoscopic treatment of maxillary and ventral rostral concal sinusitis in 60 horses. Veterinary surgeon. 2009; 38 (5): 613-619. doi: 10.1111 / j.1532-950X.2009.00556.x