Surgery of the nasal planum in the dog

ANATOMY

The nasal planum (NP), or nose pad, is the most rostral portion of the outer surface of the nose. It is pigmented, hairless and with a vertical incisure on the medial sagittal plane extending from the ventromedial angle of the nares to the upper lip, the philtrum.

Anatomically, the nasal planum differs from other cutaneous tissues: the many keratinocyte layers are covered with a thick, lamellar stratum corneum that makes it compact and protects it from external insults. The nasal cavities, extending from the nares to the choanae, are split longitudinally by the nasal septum into two nasal fossae; the nasal concha originates from the lateral and dorsal walls of the nasal cavity while the air passages form the nasal meatuses. Externally, the PN is supported by a cartilaginous and symmetrical scaffold: the dorsal lateral nasal cartilages support and shape the wings of the nares (ala nasi), while the ventral lateral nasal cartilages, continuous with the cartilage of the septum, form the floor and side wall of the nasal vestibule.

The cartilages of the external nose are supported by several ligaments: the dorsal nasal ligament connects the dorsal midline of the nasal bone to the dorsal lateral nasal cartilage, while two pairs of lateral nasal ligaments provide lateral support. The muscles of the lips, nose and muzzle, inserted into the cartilage scaffold, allow a minimal movement of the nose. The levator nasolabialis extends from the dorsal midline of the muzzle, at the level of the frontal and maxillary bones, and inserts into the upper lip and nose. Thin and flat, this muscle is located just under the skin and raises and widens the nostrils, assisted by the levator labii superioris  and the levator anguli oris muscles, while the orbicularis oris muscle distends the nose ventrally, allowing the dog to sniff downwards. The above muscles are innervated by the facial nerve.^1,2,3

PHYSIOLOGY

At rest, dogs breathe through the nose: the inspired air is warmed and humidified by the rostral portions of the nasal mucosa, while the mucosa itself is cooled by this interaction. During physical exercise, or in case of high ambient temperature, the dilation of the blood vessels that make up the rich vasculature of the nasal mucosa increases the heat and moisture exchange. With intense physical exercise, or extreme temperatures, dogs breathe with their mouth open, in order to accentuate evaporative cooling by means of a larger oral mucosa surface area.^4.5 The caudodorsal portions of the nasal mucosa are instead mostly responsible for olfaction. Dogs, in particular, tend to sniff rapidly instead of inhaling normally: it is believed that the inflow of fractionated, high-velocity air causes turbulence in the nasal cavity, directing the air into the dorsal meatus and generating a constant flow of new smells.^5,6 Having no hair follicles or glands, in dogs the wet appearance of the nasal planum is guaranteed by continuous licking, by the secretions of the lateral nasal glands and, to a lesser extent, by the secretions of the accessory medial nasal glands. The presence of IgA in such extremely serous secretions is suggestive of a possible defensive function.^1,2,5,7

DIAGNOSTICAPPROACH

CLINICAL HISTORYANDGENERAL PHYSICAL EXAMINATION

The canine PN is subject to many disorders, the aetiology of which may be immune-mediated, infectious, metabolic, endocrine, neoplastic or environmental (Table 1).¹⁰

Table 1. Diseases of the nasal planum of different aetiology.

Since many of these disorders are characterized by the presence of macroscopically similar lesions, a bioptic examination is necessary to establish a definitive diagnosis. In the course of the disease, the PN can vary in appearance, acquiring different shapes, texture and colour;⁹ dogs are typically taken to the Vet in view of the presence of neoformations, ulcers, nasal discharge, sneezing, stertorous breathing (inspiratory snoring) or depigmentation. Clinically, in one or both nares the air-flow can be from reduced to absent, with obstruction of the nasal passage caused by the presence of a mass or of fluid;⁸ in case of enlarged regional lymph nodes an aspiration biopsy must be included in the diagnostic workup.⁹

When the above clinical conditions are present the differential diagnoses must include: cancer (adenocarcinoma, squamous cell carcinoma, lymphoma, etc.); stenotic nares; inflammatory polyps; fungal, viral or bacterial infections; foreign bodies; dental disease and idiopathic rhinosinusitis.¹

IMAGING TECHNIQUES

In the dog, radiographic examinations, computed tomography (CT) and magnetic resonance imaging (MRI) are commonly used in the assessment of potential PN diseases, as well as  to identify the eventual lysis of surrounding bones (palatine and maxillary bones) in case of particularly advanced neoplastic diseases.³ Thanks to cross-sectional images these methods can in fact provide more detailed information on the complex architecture of the nose, they assist in the surgical planning and help in devising a possible radiation therapy in case of malignancy^1,3 (Fig.1).

A radical resection should not be performed without a prior full understanding of the extent of the disease.^1,26

LABORATORY TESTS

Endonasal tumours do not usually cause clinical manifestations at the level of the PN. Cytological sampling of a PN neoformation can be performed by direct imprint (after cleaning of the part to avoid incurring in falsely negative results), by needle aspiration or by impression from a bioptic sample. The cytological examination should only be considered as a preliminary test; in most cases a biopsy with histological examination is in fact necessary.^1,3

NEOPLASTIC CONDITIONS OF THENASAL PLANUM

In the dog, PN tumours are quite rare; squamous cell carcinoma (SCC) is the most common form, characterized by the possible involvement of also the mucosa of the nares.^12,13,14 Animals that are poorly pigmented and exposed to solar UV radiation are at risk of actinic dermatitis, which may evolve into SCC (Fig.2).

The potentially curative treatment of choice is surgery but, due to the aggressiveness of SCC, which tends to invade the adjacent soft tissues and bones, exeresis of the PN may have to be associated with the concomitant resection of the incisive bone and of part of the nasal and maxillary bones. PN SCC responds well to radiation therapy (RT), used as the sole initial treatment, but in most cases it is followed by an early relapse.¹² In the presence of small, superficial tumours, without caudal extension, a partial excision of the PN is possible.¹

Other tumours reported in literature are:  lymphoma,¹⁵ fibrosarcoma,^16,17 malignant histiocytosis,¹⁸ malignant melanoma,¹⁹ lymphomatoid granulomatosis,¹⁹ basal cell carcinoma,¹⁹ fibroma,¹³ mast cell tumour,²⁰ haemangioma, haemangiosarcoma,²³ eosinophilic granuloma²² and papilloma virus lesions.^24,25

RESECTIONOF THE NASALPLANUMANDRECONSTRUCTION

SURGICAL PLANNING

In the presence of SCC the complete surgical removal of the PN may be potentially curative, but it may indeed be difficult to obtain clean, non-infiltrated margins. To avoid tumour infiltration of the margins the incisive bone must often be removed, even in the absence of radiographic evidence of bone invasion. In view of the significant aesthetic alterations associated with nosectomy, i.e. the radical surgical excision of the PN, before surgery adequate communication with the owners is essential. In order to reduce intra-operative surgical pain, emergency blocks  of the infraorbital n. - which emerges bilaterally at the level of the infraorbital foramen - may be performed. Being the anatomical area densely vascularized, intraoperative bleeding can be significant; for this reason, in addition to an appropriate fluid therapy during surgery it is also recommended to have blood products available for use in the perioperative period.

SURGICAL TECHNIQUE

Acomplete resection of the PN and of the underlying incisive bone is performed using a pneumatic oscillating saw, after dissection of the soft tissues around the circumference of the nose pad. During the procedure it is necessary to control the bleeding resulting from the dorsal and lateral nasal arteries and from the greater palatine arteries.

Although in the dogthe combined resection of the PN and of the incisive bone is relatively easy to perform, the greatest problems are encountered in the subsequent reconstruction phase. Different skin reconstruction techniques are available, however the complications described are not infrequent.^1,26

A) A first technique uses a continuous purse-string suture all around the resection line so as to limit the opening and to allow a subsequent healing by second intention: apart from the resulting unnatural look, this technique may result in a full or partial obstruction of the external nares.

B) An improvement of the technique has been achieved by suturing the skin to the nasal mucosa, allowing primary healing of the wound and a reduction in both the formation of granulation tissue and in healing time. However, in both cases, the nasal turbinates remain visible and the margins of the nasal opening are only covered by exposed scar or granulation tissue; in addition, the epithelium of the muco-cutaneous junction is so thin as to be easily abraded, with the consequent formation of small chronic ulcers. Consequently, these techniques do not allow an optimal healing, as they are based on healing by second intention or on the presence of a very fragile scar tissue exposed to underlying hard structures such as cartilage or bone. These issues, combined with normal dog behaviour – i.e. the use of the nose to explore the environment - can determine a difficult recovery, possible infections, chronic ulcers and excessive scar tissue formation with subsequent stenosis of the nasal orifice.

C) A new reconstruction technique, described by Gallegos et al. (2007), makes use of the advancement and rotation of two muco-cutaneousbuccal flaps. Once the resection of the PN has been performed, in combination with a bilateral rostral maxillectomy of the incisive bone (Fig. 3-A-B-C-D), the remaining labial flaps are carefully assessed, as their size and shape vary depending on the amount of tissue removed and on the nasal conformation of the patient. The hairless pigmented margin of the upper lip is then advanced rostrodorsally in order to cover the nasal turbinates, thus creating a facsimile of the nose. The remains of the alar fold are removed, in order to open the rostral orifice of the nasal cavity (Fig. 3-E), while the exposed portion of the nasal septum is covered with the adjacent mucosa using a continuous suture pattern.

The lips are then rotated dorsally,  bringing their apexes on the dorsal midline (Fig. 3b, F-G), while the vestibular mucosa is sutured to the ipsilateral nasal mucosa all around the circumference of the newly created nasal opening (Fig. 3b, H). To separate the nasal cavity from the oral one, two symmetrical diverging incisions are performed on the labial mucosa, which are then sutured together. These incisions extend dorsolaterally from the sagittal midline of the nasal orifice until the dorsal margin of the lip, terminating where the new philtrum will be created (Fig. 3, I-L-M). Ideally, the correct positioning of the new philtrum should be such as to allow the creation of a sufficiently patent new nasal orifice which should allow an adequate air flow.

In agreement with published literature, the Author confirms  good wound healing by first intention following direct mucosal apposition, an excellent soft tissue cover of the exposed nasal concha and, ultimately, a good final aesthetic result, with the creation of an acceptable facsimile of the nose pad (Video 1). This technique has several functional advantages: it provides for the separation of the nasal cavity from the oral one and uses the lips for the nasal reconstruction, thus placing at the level of the mucocutaneous junction a tissue which is physically more robust and suitable compared to the previously used techniques. Of even greater impact is the possibility of performing the reconstruction via primary apposition of the mucosa, allowing wound healing by first intention at the level of the nasal orifice and of the mouth. With this three-dimensional reconstruction, the soft tissues form a resistant barrier against infection and facilitate healing by covering the rigid structures of the nasal bones, as well as of the cartilage and septal residues, thus protecting the turbinates from environmental traumas (Figs. 4 and 5). The use of the hairless pigmented lip margin not only apparently reduces the postoperative complication rate, but also improves the long term duration of the skin plasty compared to previous reconstruction techniques. In addition, before Gallegos et al. (2007) only minimal attention was being paid to the final cosmetic result, with consequent frequently poor final aesthetic results which, in our experience, may determine a psychological barrier in both veterinarians and owners against a surgical intervention which is instead potentially curative.

The reported postoperative complications are relatively common and include dehiscence, postoperative stenosis and bleeding. In addition, some technical modifications may become necessary depending on the individual patient and the extent of the excision; this said, the description provided may serve as a model for the surgical approach.

The creation of a patent nasal orifice can be difficult, as the labial flaps tend to collapse, acquiring a more closed position; however, this complication may be prevented thanks to careful skin trimming and suturing. In addition, traction sutures can be placed in the deep tissue of the buccal flaps at 10 and 2 o’clock of the nasal opening, anchored to the maxillary periosteum. If the tumour does not involve the floor of the nasal cavity it may not be necessary to remove the rostral aspect of the incisive bone. In such cases, however, the nasal reconstruction can be more difficult because of the greater distance that the labial flaps must cover in order to cover the incisor teeth.

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