Paranasal sinus: bone flap technique - standing surgery in Horses (Equis) | Vetlexicon
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Paranasal sinus: bone flap technique – standing surgery

ISSN 2398-2977

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  • Standing sinus surgery offers an alternative to sinus surgery under general anesthesia Paranasal sinus: bone flap technique:
  • A thorough knowledge of the relevant anatomy is essential.
  • The procedure can be used for diagnostic and therapeutic reasons.
  • The most commonly treated conditions are primary sinus empyema, sinus cysts, mass debulking, and progressive ethmoid hematomas.


  • The procedure can be used for diagnostic and therapeutic reasons.
  • The most commonly treated conditions are primary sinus empyema, sinus cysts, mass debulking, and progressive ethmoid hematomas.


  • No risk of general anesthesia.
  • Better orientation of the anatomy with less engorgement from recumbency.
  • No cost of general anesthesia.
  • Less blood loss than in a recumbent horse.
  • Less engorgement of anatomical structures.


  • Requires a thorough knowledge of the anatomy of the head and the sinuses:
    • Inadequate anatomical knowledge can result in severe hemorrhage necessitating a GA and tamponade packing of the sinuses.
    • Inadequate knowledge of the procedure can → damage of the nasolacrimal duct or infra-orbital canal.
  • Not recommended for sinonasal fenestration or for dental repulsion Teeth: repulsion.

Technical problems

  • Trephines of a suitable size can be difficult to obtain and to sharpen:
    • Bone flap creation with an oscillating saw/mallet and osteotome results in a more cosmetic outcome.
  • The horse must be kept quiet on a proper headstand.
  • Certain sinus conditions, such as sinusitis or neoplasia, may increase hyperalgesia and render the patient reactive.
  • Good quality radiographs Head: radiography 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.

Alternative techniques

  • Sinus surgery under general anesthesia Paranasal sinus: bone flap technique:
    • Usually reserved for procedures such as neoplasia removal or tooth removal.
  • Standing and surgery under GA can be performed in which the bone flap is preserved and replaced:
    • The flap can either be cut on three sides and bent backwards at the fourth side or cut on all four sides.
    • The flap can be replaced, and the periosteum sutured with absorbable suture material before subcutaneous and skin closure.
    • The flap can be replaced using stainless steel wires passed through small drill holes:
      • This procedure requires some extra time and equipment and does not necessarily improve the cosmetic outcome over flap replacement and periosteal suturing.

Time required


  • 15 min for sedation, clipping and prepping.


  • Depends on the pathology.
  • 20 min to 1 h.

Decision taking

Criteria for choosing test

  • Applicable to most causes of sinus pathology but not recommended for tumor removal, dental repulsion or sinonasal fenestration.

Risk assessment

  • Examination of patient to ensure safe sedation.
  • Patient must be reasonably tractable.



Veterinarian expertise

  • Requires a thorough knowledge of the anatomy of the head and the sinuses.
  • Requires a thorough understanding of the procedure.
  • Requires knowledge of local anesthesia, including some dental blocks (maxillary nerve block or infraorbital nerve block)

Anesthetist expertise

  • Knowledge of sedation of horses.
  • Must be prepared to anesthetize horse if unchecked hemorrhage occurs.

Nursing expertise

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

Other involvement

  • A competent horse handler to hold the horse on a headstand is critical.

Materials required

Minimum equipment

  • General surgery pack.
  • Trephine:
    • 50-57 mm bone trephine (Horsleys or Galt trephine) for the frontal flap Trephine: skull 02can use a smaller trephine used in overlapping circles (Olympic rings).

This may → an excessive periosteal reaction Paranasal sinus: standing bone flap technique 14 - lateral radiographor 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.
  • Chambers mare catheter.
  • Sponge forceps.
  • Rongeurs.
  • Proper head stand.

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 light.
  • Intra-operative radiograph equipment.
  • Negative pressure canister and sterile suctioning tubing.
  • Sterile nasogastric tube and pump for lavage OR pressure bag and solution set.

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.
  • Sterile gauze.
  • Local anesthetic solution - 2% mepivacaine Mepivacaine.
  • Needles and syringe for local anesthesia.
  • 1% povidone-iodine solution Povidone-iodine or other sterile scrub.
  • Sterile saline.

Ideal consumables

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



Dietary preparation

  • Standard dietary modification (muzzle for 60 min after last dose of sedation).

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.
  • It may be useful to 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

  • Useful to place an intravenous catheter for multiple sedation doses.
  • If hemorrhage is expected, cross-matching the patient to a readily available blood donor may be useful.


  • Headcollar.
  • Assistant to apply counter pressure against the trephining procedure.



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 - Local infiltration

  • 2% mepivacaine Mepivacaine.
  • Frontal flap site: 20 ml injected SQ over the area for the flap.

Often the local can be injected via one or two needle sites as the local anesthetic dissects between the skin and the bone allowing it to spread.

Core procedure

Bone flap
Step 1 – 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.

Step 2 - 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 allows accurate repositioning of the flap and mitigates flap depression into the 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.

Step 3 - 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).

Maxillary sinus flap

  • Elevate flap as above.

Step 4 - 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.

Step 1 - Incision

  • The trephine is used to make an impression in the area of skin infiltrated with local anesthetic .
  • A semi-elliptical shaped, laterally based skin flap is made:
    • Flaps can be made medially based, but this makes bilateral flap surgery difficult.
    • The incision is made through the skin, SQ and periosteum in one incision.
  • The flap is elevated from the underlying bone in one layer .
The skin flap must be at least 10 mm wider than the proposed trephine hole in the bone to allow closure of the skin which is supported by underlying bone. 

Step 2 - Trephining

  • A trephine hole is made through the bone and the bone flap is discarded   Head: trephination.
  • Local anesthetic is then sprayed into the interior of the sinuses.

Sinus exploration

Frontonasal flap/trephine

  • The frontonasal flap allows inspection of the frontal and caudal maxillary sinus.
  • Sinuscopy Paranasal sinus: sinuscopy with flexible endoscope may be helpful if a trephine procedure was performed .
  • The bulla of the rostral maxillary sinus is evident in the rostral aspect of the flap:
    • The bulla is a part bone/part membranous structure which separates the caudal maxillary sinus from the rostral maxillary sinus/ventral conchal sinus.
    • The bulla can be removed with rongeurs - this then uncovers the rostral maxillary sinus and the rostral extent of the infra-orbital canal.
    • Medial to the infra-orbital canal is the ventral conchal sinus.
  • The sinuses should be explored and any abnormalities identified:
    • Intrasinus masses, eg sinus cysts or progressive ethmoidal hematomas Ethmoid: hematoma should be removed.

Maxillary flap/trephine

  • The maxillary flap allows for inspection of the caudal and rostral maxillary sinuses.
Take care to avoid damage to tooth roots within the maxillary sinuses, especially in younger horses.
  • The bony septum between the two may be broken down to facilitate better communication between all sinuses.
  • The bony septum ventral to the infraorbital canal may be broken down to access the ventral conchal sinus.

Sinus 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 l 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).
  • 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 draining tracts and a nidus for infection.If packing was placed exiting out the corner of the flap, the flap may be temporarily closed with skin staples and packing removed and sinus re-explored 24-48 h later.

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

  • Monitor the incision.


Antimicrobial therapy

Other medication

Wound Protection

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

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.



  • 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 Paranasal sinus: standing bone flap technique 09 - sequestrum removalParanasal sinus: standing bone flap technique 13 - abscessParanasal sinus: standing bone flap technique 15 - sinus cyst removal.
  • 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.


  • Depends on the underlying pathology but generally good for resolution and very good for a diagnosis.

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Barakzai S Z & Dixon P M (2014) Standing equine sinus surgery. Vet Clin 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.
  • 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.
  • Quinn G C, Kidd J A & Lane J G (2005) Modified frontonasal sinus flap surgery in standing horses: surgical findings and outcomes of 60 cases. Equine Vet J 37 (2), 138-142 PubMed.
  • Schumacher J & Perkins J (2005) Surgery of the paranasal sinuses performed with the horse standing. Clin Tech Equine Pract 4 (2), 188-194 VetMedResource.

Other sources of information

  • Nickels F A (2012) Chapter 43 - Nasal Passages and Paranasal Sinuses. In: Equine Surgery. 4th edn. Eds: Auer J A & Stick J A. W B Saunders, USA. 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.