Failed FESS: Spectrum of CT findings in the Frontal Recess

PRESENTED BY:DR. HIMANSHU GUPTA

DNB JR 129.02.16

Anatomy of the FrontalRecess and Common Variants

• The Anatomic “TIGHT SPOTS”:

1. Frontal Recess2. Ethmoid infundibulum-middle meatus3. Spheniethmoidal recess

• These 3 areas are implicated as most common sites of obstruction leading to sinusitis.

FRONTAL RECESS:

• It can be conceptualized as an inverted funnel within the anterior ethmoid complex through which the frontal sinus drains.

• The tip or apex of the funnel lies at the frontal sinus ostium, which can be easily identified on sagittal CT images as a “waist” located at the level of the nasofrontal process, which demarcates the level of the floor of the frontal sinus.

• The frontal recess typically flares out inferiorly and posteriorly to form the wider opening of the funnel.

Normal frontal recess anatomy. Coronal (a) and sagittal (b) CT images show the right frontal recess (dotted red line), which is bounded anteriorly and laterally by an agger nasi cell (white arrow) and a type1 frontal cell (black arrow), medially by the middle turbinate, and posteriorly by the ethmoid bulla and bulla lamella. The nasofrontal process (arrowhead in b) forms the floor of the frontal sinus and demarcates the level of the frontal sinus ostium.

Boundaries of FRONTAL RECESS:

• Anteriorly: Agger nasi cells• Medially: Most anterior and superior portion of

middle turbinate.• Posteriorly: Ethmoid bulla, Bulla lamella,

Suprabullar cell.• Laterally: Lamina papyracea

• From the frontal recess, secretions drain to the middle meatus of the nasal cavity.

Frontal Recess cells:• The frontal recess may be pneumatized by various

anterior ethmoid cells, which are collectively known as frontal recess cells.

• The clinical relevance of frontal recess cells lies in their potential for causing frontal sinusitis by obstructing frontal sinus outflow at the level of the frontal recess.

• Any endoscopic surgical procedure aimed at clearing frontal recess obstruction must address these variant cells; failure to do so may result in surgical failure.

Frontal Recess Cells:

Anterior Group

1. Agger Nasi2. Frontal cells:

Type 1Type 2Type 3Type 4

Posterior Group

1. Supraorbital ethmoidal cell

2. Frontal bullar cell

3. Suprabullar cell

Medial Group

Inter-frontal sinus septal cells

Anterior : Agger Nasi cells• Agger nasi is a Latin term literally meaning “nasal

mound”.• At rhinoscopy, the agger nasi appears as an

eminence located on the lateral nasal wall at the leading edge of the middle turbinate.

• It represents the intranasal portion of the frontal process of the maxilla.

• Pneumatization of the agger nasi results in so called agger nasi cell.

• Agger nasi cells are considered the most anterior of all ethmoid cells.

Agger nasi cell : Coronal (a) and parasagittal (b) drawings show the location of theagger nasi cell (blue area), which forms part of the anterior and lateral boundaries of the frontal recess.

Anterior:Frontal cell Type 1 Type 1 frontal cells are most common type seen in

37% cases.

They are defined as single anterior ethmoid cells within the frontal recess sitting above the agger nasi cell.

These cells do not extend into the frontal sinus.

Type 1 frontal cell : Coronal (a) and parasagittal (b) drawings show a type 1 frontal cell (blue area) sitting atop an agger nasi cell anteriorly in the frontal recess.

Anterior:Frontal cell Type 2

• 2nd most common type of frontal cell seen in 19% of cases.

• These are defined as a tier of two or more anterior ethmoid cells sitting above the agger nasi cell.

• These cells do not extend into the frontal sinus.

Anterior:Frontal cell Type 3• Seen in 6-8% cases.

• Type 3 cells are defined as a single massive cell sitting above the agger nasi cell and pneumatizing into the frontal sinus.

Type 3 frontal cell : Coronal (a) and parasagittal (b) drawings show a type 3 frontal cell (blue area) sitting atop an agger nasi cell. The type 3 cell extends superiorly from the frontal recess through the frontal ostium and into the frontal sinus.

Anterior:Frontal cell Type 4• Rare variant. Seen only in 2.5% cases.

• It is unique among the frontal cells in that it does not abut the agger nasicell.

• These are isolated air cells located within the frontal sinus, bordered anteriorly by the anterior frontal sinus table, with their posterior walls representing free partitions in the frontal sinus.

Type 4 frontal cell. (a, b) Coronal (a) and parasagittal (b) drawings show a type 4 frontal cell (blue area) situated entirely within the right frontal sinus and bordered by the anterior frontal sinus wall. The type 4 cell does not abut the agger nasi cell. (c, d) Coronal (c) and sagittal (d) CT images show an opacified type 4 frontal cell (arrow) in the frontal sinus

Type 4 frontal cell. (a, b) Coronal (a) and parasagittal (b) drawings show a type 4 frontal cell (blue area) situated entirely within the right frontal sinus and bordered by the anterior frontal sinus wall. The type 4 cell does not abut the agger nasi cell. (c, d) Coronal (c) and sagittal (d) CT images show an opacified type 4 frontal cell (arrow) in the frontal sinus

Posterior group ofFrontal recess cells

• All of the cells in this group are located along the posterior wall of the frontal recess and are bordered posteriorly or superiorly by the anterior skull base.

Posterior:Supraorbital Ethmoid cells• They extend superiorly and laterally over the orbit

from the frontal recess.

• These cells represent pneumatization of the orbital plate of the frontal bone posterior to the frontal recess orbit from the frontal recess and the frontal sinus.

• They typically drain into the lateral aspect of the frontal recess.

• Present in 15% of the individuals.

Supraorbital ethmoid cell. (a) Coronal CT image obtained slightly posterior to the level of thefrontal recess shows a supraorbital ethmoid cell (arrow) extending over the left orbit. The opening of this ethmoid cell is closely related anatomically to the canal for the anterior ethmoid artery (arrowheads). In this case, it would be difficult to distinguish this cell from posterior pneumatization of the frontal sinus on the basis of coronal images alone. (b) Axial CT image shows the supraorbital ethmoid cell (arrow), which is clearly differentiated from the frontal sinus (*) by a discrete bony septum.

Posterior:Frontal bullar cells These cells represent pneumatization of the

anterior skull base in the posterior frontal recess with extension into the true frontal sinuns.

These cells lie above the ethmoid bulla and, when present, define a portion of the posterior boundary of the frontal recess and frontal sinus.

Frontal bullar cell : Parasagittal drawing shows a frontal bullar cell (blue area), which is situated along the posterior boundaryof the frontal recess and pneumatizes into the frontal sinus.

Posterior:Suprabullar cell Suprabullar cells are nearly identical to frontal

bullar cells, with the only distinguishing feature being that suprabullar cells lie entirely below the level of the frontal sinus ostium and do not extend into the frontal sinus.

Like frontal bullar cells, suprabullar cells sit above the ethmoid bulla and form a portion of the posterior wall of the frontal recess.

Suprabullar cell : (a) Parasagittal drawing shows a suprabullar cell (blue area) situatedalong the posterior boundary of the frontal recess. (b) Sagittal CT image obtained through the frontal recess shows a large suprabullar cell (arrow) sitting above the ethmoid bulla (*) and situated along the posterior aspect of the frontal recess. The cell is bordered superiorly by the skull base; however, unlike a frontal bullar cell, the suprabullar cell does not extend above the level of the frontal ostium into the frontal sinus.

Frontal Bullar cell Suprabullar cell

During endoscopic frontal sinusotomy, both suprabullar and frontal bullar cells can be mistaken for the skull base; thus, failure to recognize their presence preoperatively can result in incomplete surgical dissection.

Common Endoscopic Procedures Used in the Frontal Recess

The frontal sinus is the most difficult of the four paranasal sinuses to treat endoscopically owing to its location and complex anatomy.

Serious complications can occur because of the proximity of the frontal recess to the anterior ethmoid artery, orbit, and anterior cranial fossa.

In addition, the region of the frontal recess is extremely susceptible to postoperative scarring, resulting in frontal recess stenosis.

For these reasons, surgical dissection in the region of the frontal recess is often avoided initially, and primary surgery for anterior ethmoid sinus disease (which may or may not involve the frontal sinus) is generally directed at the anterior ostiomeatal complex.

Tyically, these surgeries consist of a combination of uncinectomy, anterior ethmoidectomy, and middle meatal antrostomy, which is generally sufficient to clear disease in the frontal sinus and frontal recess.

Septoplasty may also be performed.

• Most endoscopic procedures directed at the frontal sinus are revision surgeries performed in patients who have already undergone failed ostiomeatal complex surgery.

• A number of endoscopic frontal sinus drainage procedures have been developed, most of which are variations on the classification system of Draf.

• The endoscopic frontal recess approaches:• 1. Draf type I frontal sinusotomy (least invasive)• 2. Draf type II procedure• 3. Modified Lothrop procedure (Draf type III procedure).

Frontal sinus drainage procedures

Draf Type I procedure:

Endoscopic frontal recess approach (Draf type I procedure). Coronal (a) and parasagittal (b) drawings show the area of resection in green. This surgery consists of removal of obstructing structures, including anterosuperior ethmoid cells (agger nasi cell and any obstructing frontal recess cells) and the uncinate process. The dissection does not extend above the frontal ostium, hence the nasofrontal beak (best seen on the sagittal image) remains.

Draf Type II procedure:

Extended frontal sinusotomy (Draf type II procedure). (a, b) Coronal (a) and parasagittal (b) drawings show the area of resection in green. This procedure can be difficult to distinguish from the less invasive endoscopic frontal recess approach (Draf type I surgery) at postoperative CT. Unlike the Draf type I procedure, Draf type II surgery includes resection of the frontal sinus floor and may extend into the frontal sinus, resulting in a less pronounced or absent nasofrontal beak on sagittal images. The posterior ethmoid cells have also been resected.

Coronal (c) and sagittal (d) CT images show the typical postoperative appearance after an extended frontal sinusotomy.The posterior ethmoid cells have also been resected.

• In addition to removing those structures typically removed in a Draf type I surgery, the Draf type II procedure also involves enlarging the frontal sinus ostium by removing any frontal recess cells protruding into the frontal sinus or by resecting the frontal sinus floor between the lamina papyracea and nasal septum, including the anterior portion of the middle turbinate.

• At postoperative imaging, it can be difficult to distinguish this procedure from a Draf type I surgery. Sagittal reformatted images can be helpful in this regard, as they will demonstrate a more extensive ethmoid resection and removal of the frontal sinus floor (the nasofrontal beak) after Draf type II surgery.

Modified Lothrop Procedure(Draf Type III procedure)• occasionally referred to as a Median drainage procedure.

• consist of contiguous bilateral enlargement of frontal sinus drainage. This is achieved by removal of the frontal sinus floor on both sides and removal of adjacent parts of the inferior inter–frontal sinus septum, superior nasal septum, and anterior middle turbinates.

• These procedures are performed for the most severe cases of recalcitrant frontal sinus disease, as an alternative to frontal sinus obliteration.

Modified Lothrop procedure (Draf type III procedure) : (a) Coronal drawing shows the area of resection in green. This procedure consists of contiguous bilateral enlargement of the frontaloutflow tract, a result achieved by removal of the frontal sinus floors and adjacent parts of the inferior inter–frontal sinus septum, superior nasal septum, and anterior middle turbinates. (b) Coronal CT image obtained at the level of the frontal recess shows these findings in addition to a defect of the superior nasal septum. This defect should not be mistaken for an unintended surgical septal perforation.

CT Findings Associated with FESS Failure in the Frontal Recess

• Most cases of recurrent frontal sinusitis after FESS can be attributed to stenosis of the frontal recess.

• The relatively common causes of frontal recess stenosis are:1. inadequate removal of the agger nasi and frontal recess cells, (most common reason for restenosis)2. retained superior portion of the uncinate process,3. lateralization of the middle turbinate,4. osteoneogenesis secondary to chronic inflammation or mucosal stripping,5. scarring or inflammatory mucosal thickening,6. recurrent polyposis.

Residual Frontal Recess Cells

Retained frontal recess cells. Postoperative coronal (a) and sagittal (b) CT images obtained through the left frontal recess show complete opacification of the frontal sinus and frontal recess. There are remnant opacified frontal recess cells, including an agger nasi cell (*) and a tier of type 2 frontal cells (arrows), which narrow the frontal ostium and frontal recess.Not only do residual air cells obstruct the frontal recess, but they also serve as platforms forscar tissue to form.

Retained Uncinate Process The uncinate process has a variable relationship to the

frontal recess, and its superior insertion dictates the direction of frontal recess drainage into the middle meatus.

When the uncinate process attaches to the lamina papyracea or the agger nasi, its anterior portion forms the lateral wall of the frontal recess, funneling frontal recess drainage directly into the middle meatus.

In these cases, the ethmoid infundibulum terminates in a blind-ending recess known as the recessus terminalis.

On the other hand, when the uncinate process attaches to the skull base or the middle turbinate, it serves as the medial wall of the frontal recess, directing secretions into the ethmoid infundibulum prior to passage into the middle meatus.

Effect of the superior attachment of the uncinate process on frontal recess drainage. Large arrow = superior aspect of the frontal recess. (a) Coronal CT image shows the uncinate process (small arrows) attached to the lamina papyracea. As a result, the ethmoid infundibulum terminates in a blind recess known as the recessus terminalis (*). In this case, frontal recess drainage (dashed red line) passes directly into the middle meatus. (b) Coronal CT image from another patient shows the uncinate process (small arrows) attached to the skull base at the junction of the cribriform plate and lateral lamella. Therefore, frontal recess drainage (dashed red line) is directed into the ethmoid infundibulum.

In patients who have not undergone surgery, one of the most common causes of obstruction at the level of the frontal recess is a medially displaced uncinate process. This occurs when disease in the recessus terminalis displaces the uncinate process medially so that it lies close to or even against the middle turbinate.

It is not uncommon for surgeons to ignore the superior attachment of the uncinate process (17), and retained uncinate processes have been reported in 37% of patients undergoing revision FESS.

if a medialized uncinate process is left behind during FESS, then the frontal recess will have a tendency to restenose postoperatively.

Retained uncinate process. Postoperativecoronal CT image obtained through the frontal recess shows a remnant uncinate process (arrow) on the left. The uncinate process is attached to thelamina papyracea and forms a recessus terminalis(*), which is opacified. The frontal recess is opacified at the level of the recessus terminalis. Also note the medialized left middle turbinate adherent to thenasal septum; this appearance is a normal and often expected postsurgical finding.

Lateralized MiddleTurbinate Remnant

In patients who have undergone middle turbinate manipulations, including partial middle turbinate resection, the amputated anterior stump may lateralize and obstruct the frontal recess.

Nonetheless, rather than resecting a middle turbinate that has become “floppy” as a result of surgical manipulation, some surgeons choose to medialize the middle turbinate by creating small abrasions on the medial aspect of the middle turbinate and on the adjacent nasal septum (a process known as “Bolgerization”), effectively causing an adhesion between the two structures

Lateralized middle turbinate remnant. Postoperative coronal (a) and axial (b) CT images show a lateralized middle turbinate remnant (arrow). The middle turbinate remnant is adherent to the lamina papyracea, narrowing and obstructing the frontal recess.

Osteoneogenesis

Osteoneogenesis. Postoperative coronal (a) and axial (b) CT images show thickening of remnant ethmoid septa (arrows), an appearance indicative of osteoneogenesis. There is associated mucosal thickening, which may represent inflamed edematous mucosa, scar tissue, or secretions, causing sinus opacification.

In normal individuals, the bony septa of the ethmoid sinuses have an average thickness of approximately 0.5 mm, with the upper limit of normal being about 1 mm.

In addition, the middle turbinate measured at its midpoint on axial images averages 1.5 mm in thickness, with a normal upper limit of 2.5 mm.

At CT, osteoneogenesis appears as thickening of the ethmoid septa or sinus walls and is often accompanied by scarring or mucosal edema.

Recurrent Polyposis

Recurrent polyposis. Postoperative coronal (a) and sagittal (b) CT images show near-complete opacification of the frontal sinuses and polypoid soft tissue completely opacifying the frontal recess, findings consistent with recurrent polyposis. Note the convex soft-tissue borders formed by the polyps (arrows in b).

Conclusion• The emergence of FESS in the treatment of chronic sinusitis

has significantly expanded the role of CT evaluation of the paranasal sinuses.

• CT is an invaluable adjunct to diagnostic nasal endoscopy in identifying various causes of frontal recess obstruction after FESS.

In addition, a working knowledge of the most common causes of surgical failure in the frontal recess, which include remnant frontal recess cells, a retained uncinate process, middle turbinate lateralization, osteoneogenesis, scarring or inflammatory mucosal thickening, and recurrent polyposis, will ensure that these entities are not overlooked during revision surgery.