Frontal Sinus Stenting Techniques

Endoscopic surgery is now commonly used in the management of simple and complex pathologies of the frontal sinus. As experience with the endoscopic technique has grown, use of these procedures for frontal sinus surgery has increased. The goals of endoscopic frontal sinus surgery include disease eradication, implementation and maintenance of an adequate drainage and ventilation pathway, and the restoration of mucociliary function.

Frontal sinus pathology is particularly challenging to treat due to the narrow and complex anatomy of the frontal outflow tract (see the images below).

Anatomy of the lateral nasal wall, schematic: (1) Sphenoid sinus, (2) anterior cranial fossa, (3) anterior ethmoid cell, (4) frontal sinus, (5) agger nasi, (6) infundibulum, (7) posterior ethmoid cell

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Anatomy of the frontal recess. The frontal recess is an hour glass-shaped space (green shaded area) with the waist at the frontal ostium and its narrowest part that drains into the ethmoid infundibulum: (1) frontal sinus, (2) frontal ostium, (3) agger nasi cell, (4) bulla ethmoidalis, (5) anterior cranial fossa, (6) infundibulum

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Stenosis of the frontal recess or failure to establish a tract can lead to disease persistence and iatrogenic complications. Postoperative stenosis of the frontal sinus outflow due to formation of scar tissue, synechiae, or osteogenesis is the most common cause of frontal sinus surgery failure. ^[1]

Stenosis of the frontal recess is best prevented by avoiding unnecessary manipulation of the outflow tract and meticulous surgical technique. Without formal frontal ostium dissection, anterior ethmoidectomy with exposure of the frontal recess has been shown to result in resolution of frontal sinus disease. ^[2] The indications for a formal frontal sinusotomy should therefore be carefully determined. If frontal recess dissection is undertaken, meticulous tissue handling with avoidance of any mucosal trauma is key to a successful outcome. Routine frontal stenting is unnecessary (see image below).

3A: Intraoperative endoscopic view of the dissected frontal ostium after total anterior ethmoidectomy and Draf 2a frontal ostioplasty (70º endoscope view): (A) nasal beak, (B) frontal neo-ostium, (C) anterior skull base. Postoperative view of frontal ostium with a 70º endoscope. 3b: Well-healed, mucosalized frontal neo-ostium 3 months after Draf 2a (frontal ostioplasty). No stent was used in this case.

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The most common cause of restenosis of the frontal sinus outflow tract is iatrogenic (postoperative scarring, adhesions, and middle turbinate lateralization). Severe inflammatory pathology, obstructive polyposis, and nonsurgical trauma are other common causes.

The incidence of persistent frontal sinusitis with symptoms after endoscopic sinus surgery is 2-11% based on numerous studies, all with relatively short follow-up. ^[3] The necessity of longer follow-up after frontal sinus surgery to determine the true incidence of disease relapse was demonstrated by Neel et al. In their study, failure rate after modified Lynch procedure increased from 7% at 3.7 years to 30% at 7 years. ^[4] Frontal sinus stenting may help prevent failure of standard endoscopic treatment of frontal sinus disease by maintaining patency and structural integrity of the frontal sinus outflow tract while regeneration of the frontal neo-ostium mucosal lining takes place. ^[5] In many situations, such as after a drill-out procedure (modified Lothrop or Draf III) for neo-osteogenesis or tumor removal, the mucosal lining is absent or significantly violated. Stenting may be useful in such situations.

Surgically placed stents to maintain ventilation and drainage of the frontal sinuses have been used for over a century. The first frontal sinus stents were gold tubes used in 1905 by Ingals. ^[5] In 1921, Lynch first described his frontoethmoidectomy technique, of which a key component was 1-cm rubber tubing used to stent the frontal sinus. ^[6] Progress in both surgical instrumentation and new stent material has been made over subsequent years. Numerous options are now available for stenting in cases that have an anticipated high risk of surgical failure. Stents differ in terms of material, shape, and the techniques used to deploy them.

Despite the long history of frontal sinus stents, no universally accepted criteria exist for their use. Stenting may be considered in a patient who has failed standard ethmoidectomy or frontal sinusotomy, or in whom a high likelihood of failure to maintain a patent recess is expected.

Authors have advocated different criteria to stent the frontal recess. The size of the frontal sinus neo-ostium created after frontal sinusotomy has been used as a guide for sinus stenting by some authors. ^{[4, 5, 7]} However, as the natural size of the recess itself is small, stenting is likely unnecessary unless extensive mucosal disruption exists. In a study correlating frontal neo-ostium size to postoperative patency, Hosemann et al found the postoperative stenosis rate of a frontal neo-ostium less than 5 mm in diameter to be 33%, whereas the stenosis rate was 16% with an intra-operative neo-ostium diameter of greater than 5 mm. ^[8] Thus, for a neo-ostium size of less than 5 mm, stenting may be indicated.

Additional indications for frontal sinus stenting include the presence of osteitic bone, purulence, or granulation indicating severe inflammatory disease. The presence of vasculitides or granulomatous disease, previous surgical failure, excessive removal or destabilization of the middle turbinate predisposing to lateralization, traumatic fracture of the frontal sinus outflow tract, ^[9] and the presence of extensively denuded or circumferentially exposed bone around the neo-ostium perimeter ^[5] are other proposed indications.

In the case of stripped mucosa surrounding the frontal neo-ostium, stents have also been used to hold a mucosal graft in place. Dubin and Kuhn described endoscopic resection of 12 frontal sinus osteomas with preservation of the natural frontal sinus outflow. They stented all cases with greater than 40% denuded frontal recess mucosa. ^[10] Some authors have also advocated using soft silastic stents in uninjured frontal recesses to assist with postoperative debridement. ^[10] The stents are removed 2-3 weeks after surgery. During removal, the adherent clots and crusts caught within the stents are reported to be more easily removed.

Frontal sinus stenting can therefore be a valuable technique to maintain an adequate ventilation and drainage pathway. In select cases, this minimally invasive procedure is a reasonable alternative to more extensive and aggressive frontal recess surgeries such as the endoscopic-modified Lothrop procedure, osteoplastic flap, or frontal obliteration. ^[5]

Relative indications for frontal sinus stenting are as follows:

• Circumferentially exposed bone (after modified Lothrop for tumor resection or extensive mucosal denudation)

• Traumatic fracture of outflow tract

• Restenosis after surgery

• Frontal neo-ostium smaller than 5 mm

• Middle turbinate destabilization

• Recalcitrant inflammatory disease (purulence, granulation, osteitic bone, polypoid obstruction, granulomatous disease)

Contraindications

No absolute contraindications exist to placement of a frontal recess stent. The key to prevention of frontal recess stenosis is meticulous mucosal preservation. Routine stenting of the frontal recess is unnecessary. Manipulation and trauma of the frontal recess during frontal stent placement and any inflammatory reaction caused by the stent itself may lead to scarring and poor healing of the recess. Concern also exists for the formation of biofilms, which are known to perpetuate an inflammatory tissue response. Stenting should only be used for limited indications for a well-defined period of time.

Best Practices

Several methods of frontal sinus stent placement exist, including both endonasal and external approaches. Endoscopic insertion is always preferable and is most commonly used. Endoscopic frontal sinusotomy should be conducted by surgeons experienced in recognizing anatomic variations, especially in the face of disease, bleeding, or distorted anatomy. An array of angled telescopes (30º, 45º, and 70º), as well as frontal instruments of various angles and lengths, are necessary for frontal recess dissection and stent placement. Computer-assisted image guidance systems are extremely helpful, and may be essential for complicated or revision cases. ^[7]

Procedure Planning

Surgical planning requires careful preoperative assessment including a thorough endoscopic examination and CT evaluation to aid in assessing the bony boundaries of the frontal recess, as well as soft-tissue anatomy. A high-definition, fine cut (1-2 mm) CT scan is recommended. The dimensions of the widest frontal recess in all 3 planes (axial, coronal, and sagittal) should be studied. The boundaries of the frontal recess are limited as follows:

• Medial - Middle turbinate

• Lateral - Lamina papyracea

• Anterior - Agger nasi

• Posterior - Bulla ethmoidalis

A narrow dimension in any plane should be noted preoperatively and stenting used as deemed necessary.

Complication Prevention

Frontal sinus stents are generally well tolerated, and the complication rate is low. Nonetheless, some concern exists that stents can serve as a potential nidus for recurrent infections (see the image below).

Frontal stents encased in crusting (A) and granulation (B). (Images courtesy of Timothy L. Smith, MD.)

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In a study by Perloff and Palmer, evidence of bacterial biofilms was found ubiquitously on silastic frontal sinus stents removed from six patients at 1-4 weeks following endoscopic sinus surgery. ^[11] The clinical significance of this finding in predisposing to recurrent infection, however, is unknown.

Stents can also serve as a source of iatrogenic obstruction of the frontal sinus outflow tract when they are trimmed too short, in which case granulation tissue can form across the stent, embedding it in place. A stent that is too long may cause crusting at the distal end, which can lead to nasal congestion and an unpleasant odor. ^[9] Avoidance of these complications requires proper trimming of the stent after insertion. Stents should be trimmed approximately to the level of the inferior border of the middle turbinate.

Toxic shock syndrome (TSS) is a rare life-threatening risk following frontal sinus stenting. ^[12] Vigilance for symptoms of TSS such as high fever, hypotension, diffuse macular erythroderma, mucosal hyperemia, mental status changes, and desquamation is required. TSS onset can occur several weeks postoperatively, as in Chadwell’s case, ^[12] in which symptoms developed on postoperative day 18 after the patient had completed a 7-day course of cephalexin. ^[12] Antibiotic prophylaxis has been relatively unsuccessful in the prevention of TSS, which is related to toxin-producing Staphylococcus aureus.

A potential for stent migration and accidental aspiration also exists. During stent removal, a theoretical risk of stent breakage can leave remnants in areas of the sinus with limited or difficult access.