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Paranasal sinus: bone flap technique

ISSN 2398-2977


  • The paranasal sinuses in the horse are commonly affected by a variety of disease processes, some of which require exploration or surgical treatment.
  • Bone flap techniques in the frontal and maxillary sinuses have been developed to allow maximum access to all parts of the paranasal sinuses for diagnosis and treatment of intrasinus disorders with superior cosmetic results.
  • Two main approaches:
    • Frontonasal flap: access to conchofrontal and caudal maxillary sinuses with additional steps for entry into rostral maxillary and ventral conchal sinuses. Most suitable for younger horses where risk of trauma to dental structures is high through a maxillary approach.
    • Maxillary sinus flap: most suitable for lesions of the rostral and caudal maxillary sinuses (especially in older horses) but by breaking down the bony plates beneath the infra-orbital canal/ventroconchal sinus and between the rostral and caudal maxillary sinuses access can be gained to other parts.


  • Exploration of paranasal sinuses.
  • Removal of tumors Respiratory: neoplasia, masses (paranasal sinus cyst, ethmoid hematoma), diseased cheek teeth, abnormal and infected mucosa.
  • Establish drainage into nasal cavity.


  • Greater access to all parts of the paranasal sinuses for visualization and surgical manipulation.
  • Flexible positioning and size.
  • Good cosmetic results.
  • The sinuses may be packed with hemostatic gauze if hemorrhage is excessive.
  • Frontonasal flap approach is superior to maxillary approach because of greater access, ease of generation and minimal hemorrhage.
  • Can be performed standing in horses that are docile and not head shy with sedation Anesthesia: standing chemical restraint and local anesthesia Anesthesia: local - overview.


Technical problems

  • Good quality radiographs or computed tomography (CT) Computed tomography of the skull is often necessary for surgical planning, especially in cases of facial distortion caused by masses or with dental pathology.
  • Requires specialized equipment such as an oscillating bone saw and/or osteotome and mallet.
  • Risk of hemorrhage is lessened if flap is performed in a standing animal or anesthetized animal can be placed into reverse Trendelenberg to elevate the head above the heart.
  • Establishing drainage through a nasal to ventral conchal fenestration is painful to the patient and may result in excessive hemorrhage.

Alternative techniques

  • Standing frontal flap sinus surgery technique Paranasal sinus: bone flap technique - standing surgery.
  • Trephination Head: trephination: gives limited access but is simple, inexpensive and can be carried out in the standing horse for biopsy, aspiration or irrigation; and under GA for selective repulsion of diseased teeth.
  • Sinuscopy (sinoscopy) Paranasal sinus: sinuscopy: exploration and collection of samples; lavage of paranasal sinuses.
  • Centesis Paranasal sinus: percutaneous centesis: collection of fluid; lavage of sinuses.
  • Minimally invasive procedures for removal of diseased cheek teeth such as lateral buccotomy may result in lower rates of complications, such as orosinus fistula.

Time required


  • Aseptic skin preparation: 10 min.
  • General anesthesia induction and maintenance: 20 min.


  • Preparation of flap, entry into sinuses and closure: 45-60 min.

Decision taking

Criteria for choosing test

  • Flaps are used where the paranasal sinuses require thorough exploration, establishment of drainage into the nasal cavity or removal of masses, eg maxillary (sinus) cysts, ethmoid hematoma lesions, neoplasms, teeth etc.

Risk assessment



Veterinarian expertise

  • Thorough knowledge of paranasal sinus and dental anatomy is critical for success.
  • Good aseptic technique.
  • Ability to assess hemorrhage and order a blood transfusion if needed.

Anesthetist expertise

  • Ability to competently anesthetize a horse under GA or sedate a horse if procedure done standing.
  • Ability to evaluate hypoperfusion resulting from blood loss including tachycardia, hypotension; ability to administer blood transfusion.

Nursing expertise

  • Assistance with a GA if required.
  • Knowledge of oscillating saw set-up if this is to be used.

Materials required

Minimum equipment

  • General surgery pack.
  • Trephine:
    • 50-57 mm bone trephine (Horsleys or Galt trephine) for the frontal flap - can use a smaller trephine used in overlapping circles (Olympic rings).This may → an excessive periosteal reaction or sequestration and worsen the cosmetic outcome. A bone flap using oscillating saw or mallet/osteotome is recommended for cosmesis.
    • A 10 mm trephine for the site of the Foley catheter in the caudal maxillary sinus.
  • Local anesthetic solution - 2% mepivacaine Mepivacaine.
  • Chambers mare catheter.
  • Sponge forceps.
  • Rongeurs.
  • Proper head stand if performing technique standing.

Ideal equipment

  • Oscillating bone saw or hammer and sharp osteotome.
  • Periosteal elevator(s) or wide (25-30 mm wide) osteotome.
  • Steinmann pins 2-3 mm.
  • Pin chuck.
  • Head torch.
  • Surgical table that may elevate the patient in reverse Trendelenberg position.
  • Intra-operative radiograph equipment.
  • Negative pressure canister and sterile suctioning tubing.

Minimum consumables

  • 2/0 absorbable suture material, eg polyglactin 910 (Vicryl ), polydioxanone.
  • 2/0 or 0 non-absorbable suture material, eg polypropylene or skin staples.
  • Sterile bandage.
  • 1% povidone-iodine solution Povidone-iodine.

Ideal consumables

  • Cotton wound packing material.
  • Sterile containers and formalin-filled containers for culture and histopathology, respectively.



Dietary preparation

  • Standard dietary modification (withhold feed 6-8 h prior to and 90 min post-operative).

Site preparation


  • Standard aseptic preparation (clean with povidone-iodine and saline, shave, swab and drape).
Do not use chlorhexidine or alcohol near the cornea.

Local anesthesia for standing cases

  • Infuse the planned incision line subcutaneously with 2% mepivacaine Mepivacaine or 2% lidocaine Lidocaine.
  • Create a small hole in the concho-frontal sinus midway between the medial canthus of the eye and the dorsal midline with a Steinman pin in a hand-held chuck. Instill 35-50 ml of chosen anesthetic into the sinuses via the hole.

Other preparation

  • Crossmatching the patient with suitable blood donors and, preferably before surgery, collect up to 8 l whole blood - store in citrate in a cool environment.




Step 1 – Identify anatomical landmarks

Frontonasal flap

  • A variety of flap types exist but all are centered between the dorsal midline and the dorsal-orbital rim on the affected sinus side.
  • Caudal edge of flap is at right angles to the dorsal midline and midway between the supra-orbital foramen and the medial canthus of the eye.
  • The lateral edge is roughly parallel to the midline and 2-2.5 cm medial to the medial canthus of the eye for 4-5 cm before angling medially to avoid the nasolacrimal duct (courses medial canthus of eye towards naso-incisive notch).
  • The rostral edge is at right angles to the dorsal midline, two thirds of the distance between the medial canthus of the eye and the infraorbital foramen, approximately 9-10 cm from the caudal edge.
  • Alternatives include a triangulated flap, or a small rectangular flap made underneath a curvilinear skin incision based at the level of the eye.
Make sure not to transect the nasolacrimal duct when making the bone flap.This flap makes an entrance into the frontal sinus but allows access to the caudal maxillary sinus and the bulla of the rostral maxillary sinus/ventral conchal sinus. 

Maxillary sinus flap

  • Centered over maxillary sinus above facial crest and rostral to eye.
  • The caudal border is at right angles to the facial crest and 0.5-1 cm in front of the medial canthus of the eye if caudal maxillary sinus to be explored.
  • The ventral border is 0.5 cm above and parallel with the facial crest if a dorsally-hinged flap is required.
  • The rostral border is from the end of the facial crest and parallel with the caudal border - if rostral maxillary sinus is to be explored.
  • If the flap is to be ventrally hinged just above the facial crest, the dorsal margin is on a line from the infraorbital canal to the medial canthus, to avoid the line of the nasolacrimal duct.

Step 2 - Skin incision

  • Incise skin to overlap the desired bone incision by 5 mm and to conform to a similar shape with rounded corners.
  • The incision should be robust enough to incise skin, subcutaneous tissues, and periosteum.
  • Small vessels may need to be ligated with 2-0 absorbable suture prior to bone flap creation.
If the procedure is to be done standing, perform local infiltration of the skin and subcutaneous tissues using 2% mepivacaine. The sinus may also need to be infused with local anesthetic prior to manipulation of intrasinus contents.


Core procedure

Step 1 - Cut bone

  • Cut bone to create a 3-sided flap:

Either with oscillating bone saw (flush bone with saline during bone saw use).
Or using a sharp osteotome and hammer.

The start points or changes in angles can be defined by puncturing the bone using a small Steinmann pin or drill bit in a handchuck, and the bone cut between these points.

Take care to avoid the nasolacrimal duct.

  • Cutting the bone at a 45° angle to allow accurate repositioning of the flap and will mitigate risk of bone depressing into sinus.
  • Maxillary sinus flap - elevate the origins of the levator labii maxillaris and levator nasolabialis muscles from the most rostral end of the flap before cutting bone.
  • Large branches of the angular artery of the eye and associated veins require elevation and preservation or if necessary, ligation and cutting.
Take care to avoid damage to tooth roots within the maxillary sinuses, especially in younger horses.

Step 2 - Elevate flap

Frontonasal flap

  • Cut small bony attachments between underside of flap and floor of frontal sinus with a wide bladed osteotome.
  • Place wide periosteal elevators and/or osteotomes under the rostral and caudal ends of the flap.
  • Prise flap open, fracturing it along the hinge line (hinge consists of skin, fascia, periosteum and incomplete bone fracture):
    • Sponge forceps with gauze protecting the skin side may aid in fracturing the flap wholly.Take care to prise the flap open, as fracturing the flap into more than one piece may result in difficulty closing.

Maxillary sinus flap

  • Elevate flap as above.

Step 3 - Sinus access

Frontonasal flap

  • Access is allowed into the conchofrontal sinus and caudal maxillary sinus.
  • Break down the bulla of the ventral conchal sinus and the rostral edge of the frontomaxillary opening to allow access to the rostral maxillary sinus and ventral conchal sinus.

Maxillary sinus flap

  • Transect the septum that divides the maxillary sinus using an osteotome.
  • Break down the sagittal bony plate beneath the infra-orbital canal to allow access to the ventral conchal sinus.
Take care to avoid damage to the infraorbital canal and nerve.

Step 4 – Lavage and establishing drainage

  • High-pressure irrigation with isotonic fluid with the aid of a sterile nasogastric tube and pump or through a solution set and 1 liter bag placed in a pressure bag allows for removal of inspissated pus and debris in the sinuses.
  • Can be performed with a garden hose with warm water or a proprietary garden sprayer.
  • Also allows assessment of the patency of sinonasal drainage through the nasomaxillary aperture.
  • If the ventral conchal bulla was broken down during a frontonasal bone flap, then better drainage may be achieved by fenestrating the rostral portion of the ventral conchal sinus Paranasal sinus: drainage ostia - enlargement:
    • Have an assistant use a Chamber’s catheter threaded with large gauge suture to fenestrate the rostral portion of the ventral conchal sinus by traveling up the ipsilateral nostril.
    • Tie sterile packing to suture once the chambers catheter can be visualized through the flap.
    • The packing may be sutured to the ipsilateral false nostril and removed 24-48 h later.
Hemorrhage after establishing this fenestration is usually marked. Furthermore, ensure the patient is well sedated prior to this step, as fenestration is uncomfortable for the patient.Pre-measure the Chamber’s catheter against the horse’s head to gauge depth of placement; injury to the ethmoids by passing the Chamber’s catheter too caudally will result in frank hemorrhage.


Step 1 - Control hemorrhage

  • Control hemorrhage (usually profuse) by packing sinuses with gauze bandage soaked in 1% dilute povidone iodine saline (or occasionally 1:10,000 epinephrine Epinephrine).

Risk cardiac arrhythmias under halothane anesthesia when using epinephrine Epinephrine.

  • Fold bandage into sinus and draw free end:

​​Either through nasal passage and suture/tie to false nostril if a fenestration was made through the ventral conchal sinus prior to packing the frontal sinus.
Or bring through the side of the head via a separate trephine hole or a corner removed from the bone flap to be removed 24-48 h later prior to permanent flap closure.

Step 2 - Repair bone flap 

  • Bend flap back down into position:

Either repair bone flap by suturing periosteum and fascia with simple continuous and interrupted absorbable sutures (2-0 or 0).
Or thread 2 polyglactin 910 or 25G stainless steel wire through small holes (2 mm) drilled in the flap and adjacent parent bone making simple interrupted sutures Surgery: suture patterns - basic patterns.

Wiring of bony portion of flap does not necessarily result in a more cosmetic outcome and may result in suture sinus formation.

Step 3 - Close subcutis

Step 4 - Close skin 

  • Close skin using non-absorbable simple interrupted sutures or skin staples.
  • Cover operative site with a stent bandage or an elastic adhesive bandage for 4-7 days.

Step 5 - Alternative method

  • Incise periosteum on 3 sides (beneath the skin incision).
  • Elevate the periosteum, subcutaneous tissues and skin in a single flap.
  • Cut 4 sides of exposed bone, elevate and discard.
  • Post-operatively: suture periosteal and subcutaneous tissues in one layer and skin separately.


Immediate Aftercare


  • Monitor for recovery from sedation.
  • Remove food and water until horse is no longer sedated.
  • Monitor for adequate airflow through contralateral nostril.
  • Monitor for blood loss if hemorrhage was severe Blood: hemorrhage - acute/chronic.

Fluid requirements

General Care

  • Upper respiratory tract (URT) obstruction may occur - a tracheotomy tube should be to hand or fitted as required Trachea: tracheotomy.

Insert a smaller tracheostomy tube, eg 20 gauge in a 450 kg horse up contralateral nostril during later stages of recovery.


Antimicrobial therapy

Other medication

  • Twice daily lavage with physiologic saline of some cases may be necessary via a needle trephine opening: paranasal sinus percutaneous centesis Paranasal sinus: percutaneous centesis for several days.
  • Close trephine hole after final lavage.
  • Ensure tetanus prophylaxis Tetanus toxoid.

Wound protection

  • Stall rest for 2 weeks to ensure no injury to flap occurs, resulting in flap depression.

Special precautions

  • URT obstruction - nasal passages - tracheotomy tube may be required Trachea: tracheotomy.
  • Excessive hemorrhage - blood transfusions may be required.

Potential complications

  • Profuse hemorrhage Paranasal sinus: bone flap technique - hemorrhage.
  • Particularly likely during fenestration from the sinuses to the nasal passages via the ventral conchal sinus.
  • Incisional dehiscence.

Long term Aftercare

Follow up

  • Suture and staple removal 10-14 days after surgery.
  • It is common to irrigate sinuses daily for up to 10-14 days post-operatively (particularly with septic and destructive intra-sinus lesions) via either a nasal or trephine placed catheter or tube (away from bone flap site).
  • Mucopurulent fluid may drain from sinuses and down nasal passages initially but should cease in 10-14 days in normal cases.



  • Wire or non-absorbable sutures in bone can cause permanent subcutaneous nodules and/or act as a nidus for infection → draining tracts from skin sutures - resolve with suture removal and local lavage/cleaning.
  • Incisional dehiscence - surgical incision is often grossly contaminated, eg due to removal of pus/debris from the sinuses.
  • Fistula formation: can be minimized by ensuring that the skin incision overlies bone.
  • Abscess formation.
  • Cosmetic outcome:
    • Poor cosmetic outcome - occurs infrequently with good surgical technique.
    • Cosmetic outcome from the frontal flap is considered good to excellent in the majority of cases.
    • Some horses show a slight concavity from the frontal flap.
    • The caudal maxillary trephine site usually leaves a small indentation scar.
Damage to infraorbital nerve may cause permanent headshaking and must be avoided at all costs.

Reasons for treatment failure

  • Inadequate debridement/removal of underlying disease process.


  • Healing of bone flaps is usually excellent despite extensive sinus infection.
  • Depends on underlying disease process.

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Barakzai S Z & Dixon P M (2014) Standing equine sinus surgery. Vet Clin North Am Equine Pract 30 (1), 45-62 PubMed.
  • Dixon P M & O'Leary J M (2012) A review of equine paranasal sinusitis: medical and surgical treatments. Equine Vet Ed 24 (3), 143-158 WileyOnline.
  • Dixon P M, Parkin T D, Collins N et al (2012) Equine paranasal sinus disease: a long-term study of 200 cases (1997–2009): treatments and long-term results of treatments. Equine Vet J 44 (3), 272-276 PubMed.
  • Tatarniuk D M, Bell C & Carmalt J L (2010) A description of the relationship between the nasomaxillary aperture and the paranasal sinus system of horses. Vet J 186 (2), 216-220 PubMed.

Other sources of information

  • Beard W (2014) Frontonasal and Maxillary Sinusotomy Performed Under General Anesthesia. In: Advances in Equine Upper Respiratory Surgery. Ed: Hawkins J. Wiley. pp 177-183 WileyOnline.
  • Nickels F A (2012) Chapter 43 - Nasal Passages and Paranasal Sinuses. In: Equine Surgery. 4th edn. Eds: Auer J A & Stick J A. Equine Surgery (Fourth Edition). W B Saunders. pp 557-568.
  • Tremaine W H & Freeman D E (2007) Disorders of the Paranasal Sinuses. In: Equine respiratory medicine and surgery. Saunders Elsevier, USA. pp 403-404.