Discussion
This report documents an optional combined frontonasal maxillary bone flap technique for the removal of large expansive hematoma from the paranasal sinuses. PEH can lead to progressive nasal obstruction and is generally unresponsive to conservative therapy (Schumacher et al 1998), for this reason radical excision is the treatment of choice (Greet 1992) with the main objective of a complete removal of the mass and the destruction of its origin (Auer et al 2019). In addition, laser surgery, chemical ablation with 4% formaldehyde solution, cryosurgery has been used in conjunction to achieve this objective (Schumacher et al 1998, Rush and Mair 2004). The choice of treatment modality dependents on the size, position, and accessibility of the lesion (Rush and Mair 2004, Auer et al 2019). Large and expansile lesions are best approached via frontal or maxillary bone flap techniques, gaining access to the origin of the lesion (Freeman et al 1990, Auer et al 2019). This surgical technique can be performed with the horse standing or under general anesthesia and exposing the nasal passages, maxillary, and frontal sinuses (Auer et al 2019).
In this case, due to the expansive nature of the hematoma and the suspected destruction of the infraorbital canal and nasolacrimal duct observed on CT scan an en bloc sinus flap was performed.
Radiographs have been shown to be a poor diagnostic imaging tool to evaluate the sphenopalatine sinus due to the superimposition of multiple anatomical structures over this axially located structure (Tucker et al 2010). In addition, endoscopy has a limitation on the visualization of the complete anatomic margins of the mass (Textor et al 2012). CT provides important anatomic information, superior lesion localization, extension and facilitates the effective treatment of horses with PEH (Tucker et al 2010, Textor et al 2012). In this case, CT examination provided extremely valuable diagnostic imaging information which allowed for detailed surgical planning and decision making for the removal of this PEH. Textor et al reported an impact of the treatment decision in 60% of the patients presented in the study after CT results (Textor et al 2012).
Surgical exploration of the paranasal sinuses is limited by the surrounding anatomical structures. The nasolacrimal duct and infraorbital nerve and canal delimitate the opening of the maxillary sinuses (Auer et al 2019). Following CT findings, it was decided to perform a complete en bloc fronto-nasal maxillary flap. This technique creates a larger opening into the sinus compartments, which allows for increased visualization and provides a comfortable space for instrument maneuverability. The expansive hematoma was successfully removed, and no complications were experienced replacing the flap into the original position.
Intra-operative hemorrhage is the most frequent and expected complication after surgical excision of PEH due to the damage of the normal nasal, sinusoidal and ethmoturbinates by the hematoma or iatrogenic during surgical removal (Freeman et al 1990, Schumacher et al, 1998 Auer et al 2019), however, no excessive hemorrhage was experienced during or after surgical removal. Also, complications associated with the damage of the nasolacrimal duct and the infraorbital nerve are rare in horses and usually linked to obstruction, trauma and compression of the duct or the canal (Roberts 2009, Robinson et al 2016). Epiphora is an expected consequence of the nasolacrimal duct obstruction, which may create chronic moist dermatitis, fly dermatitis or infectious keratoconjunctivitis (Robinson et al 2016), furthermore, head shaking, and facial pain behave have been correlated with injuries of the infraorbital nerve in horses. In this case, no post-operative complications previously reported were noted. In addition, pneumonia has been reported as a potential complication of permanent tracheostomy in adult horses (Chesen and Rakestraw 2008), also, Freeman et al reported a case that developed pleuritis and pneumonia 3 days post-operative after the removal of an osteoma through a large fronto-nasal bone flap. In this case the suspected primary source of infection was the aspiration of the sinus discharge and devitalized-necrotic tissue post-operatively, standing surgery, necessitating prolonged head elevation in conjunction with the temporay tracheostomy opening likely played a role in the development of bilateral pleuropneumonia. Furthermore, no deficits were observed.
Prognosis for PEH is unfavorable without treatment because the lesion is progressive and eventually causes obstruction and dyspnea (Rush and Mair 2004, Auer et al 2019). Lesion recurrence rates have been reported to be between 13- 45% within 18 months of surgical intervention. The recurrence after routine surgical removal is relatively high with a 43% chance of lesion recurrence (Rush and Mair 2004, Auer et al 2019). However, success rates have been shown to be greater when all lesions identified on CT were treated, and there is no involvement of the sphenopalatine sinus (Textor 2012, Auer et al 2019). In this case, the PEH had reoccurred 3 months post-operatively. The recurrent lesion was smaller and hadn’t shown any signs of progression, for this reason the owner elected monitoring for further progression and recheck endoscopic appointments.
In conclusion, a complete frontonasal maxillary bone flap can be performed safely in horses. Understanding that sedation and local anesthesia for the treatment and removal of large sinus masses, increases the rate of complication which has been previously reported in the literature. The major limitation is the requirement for a CT scan to obtain detailed imaging of the head to determine the integrity of the nasolacrimal and infraorbital canal. No neurologic or ophthalmic complications developed in this case post-operative.