Chapter 10
Frontal Sinusotomy—Draf IIb
Henry P. Barham, and Vijay R. Ramakrishnan
Introduction
- ▪ Endoscopic sinus and skull base surgery has become an effective part of the management of chronic rhinosinusitis (CRS) and tumors of the sinuses and anterior skull base. Technologic advances have been critical in advancing endoscopic surgical procedures, with the introduction of improved optics and lighting, advanced instrumentation, and image-guided surgical navigation. Hemostatic materials and devices have similarly evolved to assist in the management of the surgical field and postoperative cavity.
- ▪ The vast majority of inflammatory frontal disease can be treated with a well-performed Draf I or Draf IIa dissection. Common causes of continued disease after a complete Draf IIa dissection include membranous stenosis, middle turbinate lateralization, osteitis, neo-osteogenesis, and prominence of the nasofrontal beak.
- ▪ Extended endoscopic approaches offer improved exposure of the frontal sinus and may be preferred over external approaches in some cases. Table 10.1 describes the advantages of such endoscopic approaches. Extended frontal sinus approaches are also useful for the resection of benign and malignant tumors of the frontal sinus. The procedure has helped to expand endoscopic techniques to include recalcitrant frontal sinus disease, frontal sinus mucoceles, cerebrospinal fluid (CSF) leaks, frontoethmoid fractures, frontal sinus tumors, and endoscopic skull base surgery. The procedure also improves the postoperative delivery of topical irrigation and tumor surveillance.
- ▪ The Draf IIb procedure is an extension of the Draf IIa dissection in the medial direction, with partial removal of the anterior-superior middle turbinate and frontal sinus floor. As in basic frontal sinus surgery, it is critical to preserve mucosa and avoid exposed bone wherever possible. Ideally, complete Draf IIa dissection is performed before progressing to Draf IIb dissection.
- ▪ Patients undergoing extended frontal approach procedures often have challenging anatomy; the use of image guidance is preferred in these cases. The progression to Draf IIb dissection commits both the patient and the surgeon to more meticulous and prolonged postoperative care.
Anatomy
Frontal Sinus
- ▪ The reader is referred to Chapter 9 for discussion and illustration of the anatomy of the frontal recess, anterior ethmoid region, and accessory frontal cells. Given the high degree of variability in pneumatization of the sinus, certain basic relationships are important to understand. The frontal sinus is a pyramidal, funnel-shaped structure. It is divided in the midline by an intersinus septum and may contain an intersinus cell. The intersinus septum separates the paired sinuses and is a surgical target for maximal expansion of outflow.
- ▪ Extended frontal sinus approaches seek to remove the floor of the frontal sinus for maximal enlargement of the outflow pathway. Fig. 10.1 shows the dissection boundaries for the Draf classification of extended frontal sinus approaches. The nasofrontal beak is the variably thick bony projection at the junction of the nasal and frontal bones. If this structure is prominent, it may narrow frontal sinus outflow. The anterior limit of dissection is the periosteal layer of the superficial glabellar cutaneous tissue. Lateral boundaries of the frontal sinus floor consist of the medial orbital wall and orbital roof. These structures are generally left undisturbed during extended frontal sinus approaches.
TABLE 10.1
Anterior Fossa and Cribriform Plate
- ▪ The olfactory fossa is the lowest point in the floor of the anterior cranial base. The skull base slopes downward in a lateral to medial direction in the coronal plane and in an anterior to posterior direction in the sagittal plane. The degree of slope is highly variable and should be studied on preoperative images. The olfactory fossa contains an anterior projection into the frontal sinus that is most easily seen in axial view (Fig. 10.2). The distance from this projection to the anterior table of the frontal sinus is referred to as the anterior-posterior (A-P) diameter.
- ▪ The cribriform plate of the ethmoid bone may vary in depth and slope and is often asymmetric.
Middle Turbinate
- ▪ The middle turbinate is expected to insert into the lateral lamella of the cribriform plate. In many patients, the most anterior aspect of the middle turbinate lies anterior to the cribriform plate and may insert into the floor of the frontal sinus.
- ▪ The anterior aspect of the middle turbinate offers a reliable landmark to identify the locations of the frontal sinus and olfactory fossa (Fig. 10.3).
Indications and Contraindications for Extended Frontal Sinus Surgery
- ▪ Indications for extended frontal sinus surgery include
- – failed prior frontal surgery, often associated with neo-osteogenesis or lateralized middle turbinate remnant (Fig. 10.4)
- – mucocele (Fig. 10.5)
- – frontal sinus unobliteration
- – need for surgical access (treatment of type 3 or type 4 frontal cell, intersinus septal cell)
- – benign or malignant tumor
- – repair of CSF leak or encephalocele
- – select trauma cases
- ▪ Relative contraindications for extended frontal sinus surgery include
Preoperative Considerations
- ▪ The disease process, radiologic findings, and goals of surgery should be reviewed thoroughly before making the decision as to which approach is most favorable.
Fig. 10.2 Sagittal magnetic resonance image (A) and axial computed tomographic scan (B) showing the location of the olfactory fossa (asterisk). The surgeon should recognize the olfactory fossa as the lowest point in the floor of the anterior cranial base (A) and be aware of its anterior projection into the frontal sinus (B). 
Fig. 10.3 (A) Coronal computed tomographic scan illustrating that the vertical portion of the middle turbinate is the medial boundary of the frontal recess (black oval). (B) Endoscopic image showing the middle turbinate (MT) attachment at the lateral lamella (LL) of the cribriform, which corresponds to the oval area in (A). ESB, Ethmoid skull base; FS, frontal sinus ostium. 
Fig. 10.4 (A) Triplanar computed tomographic (CT) image guidance display and intraoperative endoscopic view for a patient who underwent prior sinus surgery with partial middle turbinate resection. A lateralized middle turbinate remnant with associated osteitis was identified as the cause of his frontal sinus obstruction. (B) Sagittal CT scan for a patient who underwent six prior sinus surgeries, most recently with placement of a frontal sinus stent. The stent was located in a supraorbital ethmoid cell with significant surrounding neo-osteogenesis. - ▪ The risks of surgery, including CSF leak, orbital injury, hemorrhage, smell dysfunction, and possible recurrence of disease, should be discussed fully with the patient well in advance of surgery.
- ▪ The possible need for adjunctive open approaches should be entertained and discussed.
- ▪ Postoperative care expectations should be agreed upon, including follow-up, débridement, and medication regimens.
- ▪ Preoperative medical treatment with agents such as antibiotics and systemic corticosteroids may be necessary to optimize intraoperative hemostasis and visualization.
Radiologic Considerations
- ▪ Thoroughly review fine-cut computed tomographic (CT) scans in the coronal, axial, and sagittal planes. Actively scrolling through the scans on a computer workstation is helpful to create a three-dimensional understanding of the anatomy.
- ▪ Examine the A-P dimension in both axial and sagittal planes. Smaller dimensions indicate a more technically challenging surgery and ultimately a smaller sinusotomy, which may yield a worse long-term prognosis.
- ▪ It is often quoted that a minimum A-P dimension of 10 mm is required, but in reality there need only be enough room for the drill to fit comfortably without the back end of the bur violating the cribriform plate or posterior table of the sinus (Fig. 10.6).
- ▪ Assess the thickness of the nasofrontal beak because this can be drilled out to increase the A-P dimension.
- ▪ Identify the middle turbinate or middle turbinate remnant. This will serve as a surgical landmark. Its anterior insertion is helpful to note preoperatively, as is the presence of lateralization, osteitis, or neo-osteogenesis.
- ▪ Establish the location of the anterior ethmoid artery and note its presence within the skull base or hanging in a mesentery. If the anterior ethmoid artery is in a mesentery, bipolar cautery may be used early in the procedure to prevent risk of inadvertent injury.
- ▪ Look for the presence of a skull base defect. It is not uncommon for a mucocele or postobstructive tumor secretions to demineralize the anterior and/or posterior table of the frontal sinus. Posterior table dehiscence warrants more careful introduction of instruments (Fig. 10.7).
- ▪ In the case of a tumor or CSF leak or encephalocele, determine the presence, location, and size of the potential skull base defect to decide on the optimal surgical approach. Magnetic resonance imaging (MRI) aids in the diagnosis of mucocele, tumor, and CSF leak or encephalocele. It may also be helpful in postoperative examination of patients who have previously undergone fat obliteration, although findings are highly variable in this population. MRI is helpful to distinguish tumor from inspissated secretions and to identify the location and size of a skull base defect.
- ▪ If far lateral dissection is expected, an adjunctive open approach, such as a trephine or osteoplastic flap, may be anticipated.
Instrumentation
- ▪ Overall instrumentation and setup are similar to that described in Chapter 9.
- ▪ In extended frontal approaches, certain equipment is particularly important:
- – 45- and 70-degree endoscopes
- – Punches, such as a 45-degree mushroom punch for thinner bone and a Hosemann punch for the thicker bone of the frontal recess
- – Angled irrigating drills: 70-degree diamond drills are the safest and most useful; however, cutting burs may be used for extensive bone removal. Extreme care must be taken with cutting burs, because misplacement or skipping of the bur can have quick untoward effects on both the orbit and dura.
- ▪ Image guidance is a surgical tool that is widely accepted by the endoscopic surgeon and used in the majority of frontal sinus surgeries. The use of image guidance can help identify critical structures and distorted anatomic landmarks, increasing the surgeon’s confidence and ability to perform a more complete dissection. Image-guided placement of limited external frontal sinusotomy allows access to and management of frontal sinus pathology that is beyond endoscopic reach while avoiding the need for an osteoplastic flap.
- ▪ Mini-trephination set: if difficulty in identification of the frontal sinus ostium is anticipated, fluorescein irrigation through a mini-trephination may be helpful.
- ▪ Materials for CSF leak repair according to the surgeon’s preferred method: these should be available in case a leak is encountered intraoperatively.
Surgical Procedure
Preparation
- ▪ The patient’s airway is maintained by either an endotracheal tube or laryngeal mask, which is taped to the lower left commissure in an effort to allow unimpeded hand mobility for a right-handed surgeon.
- ▪ The patient is prepared topically with 1% ropivacaine and 1:2000 adrenaline-soaked neurosurgical cottonoids placed within the inferior meatus and over the anterior head of the inferior turbinate.
- ▪ Endoscopically, the mucosa is injected with 1% ropivacaine and 1:100,000 adrenaline at the middle turbinate, lateral wall anterior to the middle turbinate, and septum near the anterior ethmoid artery or swell body.
- ▪ The patient’s head is placed in the neutral anatomic position, and the operative bed is placed in 15- to 20-degree reverse Trendelenburg with total intravenous anesthesia.
Surgical Technique
Step 1: Anterior Ethmoid and Frontal Recess Dissection
Step 2: Localization of the Anterior Ethmoid Arteries
- ▪ Identify the location of the anterior ethmoid arteries at the skull base. This will be the posterior boundary of the frontal dissection on each side. Attempt to directly visualize and follow the skull base anterior to the artery. This may require opening the supraorbital ethmoid cell(s) and connecting these cells to the frontal ostium if this has not already been done. If this area has been completely replaced by neo-osteogenesis, then stop and attempt to perform this dissection on the contralateral side. Do not hesitate to cauterize the artery if there is a concern it will impede later dissection. It is far better to cauterize early than to injure it later in the dissection (Fig. 10.8).
Fig. 10.8 View of the left frontal recess through a 70-degree endoscope. The frontal sinus (FS) is anterior to the supraorbital cell (SO), and the artery is seen behind a smaller second supraorbital cell (asterisk). The artery heads anteriorly as it courses from the orbit into the lateral cribriform.
Step 3: Enlargement of the Frontal Sinus Ostium
- ▪ Identify and enlarge the frontal sinus ostium and imagine the horseshoe shape of the floor of the frontal sinus. Mentally trace the path under direct visualization and confirm this with the image guidance probe.
- ▪ If the frontal outflow is substantially narrowed, such as in the case of significant neo-osteogenesis, mini-trephination with fluorescein irrigation may be considered to help direct the endoscopic dissection at this point.
Step 4: Partial Resection of the Anterior Middle Turbinate
- ▪ Partially resect the anterior middle turbinate. Carry out the resection unilaterally for the Draf IIb approach. The most inferior portion of the middle turbinate can be preserved for potential maintenance of function.
- ▪ Use curved endoscopic scissors to make a superior cut just below the anterior attachment at the skull base toward the level of the anterior ethmoid artery. Make a second cut from the inferior aspect of the turbinate and angle it to meet the first cut. Scissor cuts are generally made conservatively and then refined with through-cutting instruments (Figs. 10.9 and 10.10).
Step 5: Initial Frontal Recess Floor Removal
- ▪ Using a 45-degree mushroom punch and more robust punches, such as the Hosemann and/or Bachert variety, punch out the floor of the sinus in an anterior to medial direction. The thickness of the bone will determine the amount of bone removal performed with a punch (Fig. 10.11).
Step 6: Further Bone Removal
- ▪ If required for a larger ostium, use a 70-degree diamond drill to gradually expand the ostium in an anterior to medial direction. It is safer to drill anteriorly first to thin out the nasofrontal beak (Fig. 10.12).
- ▪ Bone removal in the anterior to medial direction can be performed with improved visualization of the skull base and intersinus septum. As bone is thinned with the drill, reintroduce punches. The serial use of punches aids in both speed and safety.
- ▪ When a prominent nasofrontal beak or severe neo-osteogenesis is present, a cutting bur may be used carefully to facilitate removal of thick bone. However, the frontal sinus proper and skull base should be definitively visualized before the introduction of the bur.
- ▪ In the Draf IIb procedure, removal of the anterior middle turbinate and ipsilateral frontal sinus floor completes the procedure.
Step 7: Cavity Optimization
- ▪ Optimize the cavity for postoperative success. Clear any purulence, bone chips, or bone dust.
- ▪ Using a bipolar cautery, cauterize the midline soft tissue just anterior to the cribriform; then, cut the edges of the middle turbinates and nasal septum.
- ▪ Medialize the middle turbinate remnants using a transseptal absorbable suture. Consider the need for dressings, such as a temporary silicone elastomer (Silastic) roll.
- ▪ If a stent is used postoperatively, thin, pliable Silastic appears more favorable for wound healing than other more rigid types of stents.
Pearls and Potential Pitfalls
Pearls
- ▪ If maxillary, sphenoid, and ethmoid surgeries are required, these procedures are performed before the frontal dissection.
- ▪ Appropriate visualization is mandatory at all times. 0- and 30-degree endoscopes are used early, when working on the anterior ethmoid and turbinates; 45- or 70-degree endoscopes are used when working within the frontal recess and frontal sinus.
- ▪ Image guidance is frequently used in these cases but is never solely relied upon. When image guidance is used, registration accuracy must be repeatedly checked on fixed landmarks.
- ▪ The working instrument is generally introduced underneath the endoscope. However, when dissecting anteriorly, it may be helpful to work with the endoscope underneath the instrument. Alternatively, the thick bone of the anterior agger nasi region leading to the nasofrontal beak can be removed to facilitate a more direct approach.
Potential Pitfalls
- ▪ Inattention to the location of the posterior surface of the drill can potentially lead to skull base penetration.
- ▪ Excessive removal of mucosa prolongs recovery and increases the potential for stenosis.
- ▪ Irregular postoperative follow-up and/or lack of meticulous medical care and débridement will certainly lead to stenosis. The neo-ostium is still maturing for up to 1 year after surgery and potentially longer if there is ongoing disease.
Postoperative Considerations
Complications
Postoperative Management
- ▪ Postoperative medical management and appropriate surgical technique are equally important in ensuring long-term patency after extended frontal surgery.
- ▪ The following medications are administered postoperatively.
- – Oral steroids are dosed and tapered according to extent of disease at surgery, endoscopic appearance in the postoperative phase, and any patient-specific factors.
- – Oral antibiotics: culture-directed therapy is preferred.
- – Irrigants: gentle saline rinses or sprays are started early.
- – Topical steroids: topical agents are started once oral steroid therapy is completed.
- – For improved frontal sinus penetration, nebulized therapy or steroid drops administered using appropriate head positioning maneuvers should be considered.
- ▪ Nasal packing is not necessary. If stents are used, there should be a rationale for their placement and duration of use. Biofilm colonization of stents has been shown at 3 weeks and likely occurs substantially sooner. Common practice is to use Silastic stents for 2 weeks, as described in Chapter 9.
- ▪ Patients should be given appropriate instructions upon discharge. Activity restrictions are similar to those for routine sinus surgeries. Patients should be counseled to recognize symptoms and signs of intracranial and orbital complications.
- ▪ Patients should receive regular follow-up with débridement as needed. This can require weekly endoscopic examinations in the clinic setting until the cavity is stable. The exact course should be tailored to the degree of disease and the endoscopic appearance of the cavity.
- ▪ Débridement may consist of the suctioning of mucus and blood clots, removal of thick fibrinous debris, early takedown of scar bands or circumferential stenosis, irrigation, direct instillation of topical steroids, or treatment of circumferential stenosis with a mushroom punch or balloon in the office.
Frontal Sinus Rescue Procedure
- ▪ The frontal sinus rescue procedure can be used to treat frontal sinus obstruction secondary to prior surgery that resulted in lateralization of a partially resected middle turbinate. In this procedure, a medially based mucosal flap is elevated from the middle turbinate stump and preserved. A Draf IIb procedure is performed, and the mucosal flap is advanced over the denuded bone. Thus, a frontal sinus rescue procedure is a Draf IIb frontal sinusotomy with an advancement flap (Fig. 10.13).