Failed Endoscopic Sinus Surgery: Spectrum of CT Findings in the Frontal Recess. RSNA 2009

1. Failed FESS: Spectrum of CT
findings in the Frontal Recess
PRESENTED BY:
DR. HIMANSHU GUPTA
DNB JR 1
29.02.16

2. Anatomy of the Frontal
Recess and Common Variants
• The Anatomic “TIGHT SPOTS”:
1. Frontal Recess
2. Ethmoid infundibulum-middle meatus
3. Spheniethmoidal recess
• These 3 areas are implicated as most common sites of
obstruction leading to sinusitis.

3. 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.

4. 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.

5. 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.

6. 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.

7. Frontal Recess Cells:
Anterior Group
1. Agger Nasi
2. Frontal cells:
Type 1
Type 2
Type 3
Type 4
Posterior Group
1. Supraorbital
ethmoidal cell
2. Frontal bullar cell
3. Suprabullar cell
Medial Group
Inter-frontal sinus
septal cells

8. 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.

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

10. 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.

11. 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.

12. 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.

14. 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.

15. 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.

17. 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.

18. 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

19. 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

20. Posterior group of
Frontal 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.

21. 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.

22. Supraorbital ethmoid cell. (a) Coronal CT image obtained slightly posterior to the level of the
frontal 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.

23. 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.

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

25. 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.

26. Suprabullar cell : (a) Parasagittal drawing shows a suprabullar cell (blue area) situated
along 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.

27. Frontal Bullar cell Suprabullar cell

28.  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.

29. Common Endoscopic
Procedures Used in the
Frontal Recess

30.  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.

31.  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.

32. • 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

33. 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.

34. 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.

35. 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.

36. • 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.

37. 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.

38. 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 frontal
outflow 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.

39. CT Findings Associated with
FESS Failure in the Frontal
Recess

40. • 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.

41. 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 for
scar tissue to form.

42. 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.

43. 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.

44.  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.

45. 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 the
nasal septum; this appearance is a normal and often expected postsurgical finding.

46. Lateralized Middle
Turbinate 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

47. 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.

48. 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.

49.  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.

50. 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).

51. 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.