Download The ethmoid bone: clinical imaging anatomy from an embryological

The ethmoid bone: clinical imaging anatomy from an
embryological point of view
Poster No.:
C-2208
Congress:
ECR 2013
Type:
Educational Exhibit
Authors:
T. Hiyama, M. Shiigai, T. Masumoto, M. Minami; Tsukuba, Ibaraki/
JP
Keywords:
Education and training, Congenital, Normal variants, Education,
CT, Head and neck, Anatomy
DOI:
10.1594/ecr2013/C-2208
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Page 1 of 74
Learning objectives
To explain imaging anatomy of the ethmoid bone from an embryological point of view.
This exhibit will be shown according to the next content list (Table 1).
Table 1: Table of contents.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
Images for this section:
Page 2 of 74
Table 1: Table of contents.
Page 3 of 74
Background
The ethmoid bone is centrally located in the paranasal sinuses, affecting drainage
pathways from the frontal and maxillary sinuses (ostiomeatal complex). It contains the
ethmoid air cells, which play an important role in olfactory sensation, humidification,
ventilation, and phonation.
The ethmoid bone consists of 4 parts: the perpendicular plate, cribriform plate, and 2
ethmoidal labyrinths (Fig 1). Because it forms the medial wall of the orbit and floor of the
anterior cranial fossa, inflammation or trauma, including endoscopic surgery, may invade
these adjacent structures. An understanding of the complex anatomy of the ethmoid
bone is therefore crucial for radiologic diagnosis of paranasal pathology and planning of
functional endoscopic sinus surgery.
Fig. 1: Ethmoid bone. The ethmoid bone is a cuboidal structure with some
prominences, forming the boundary of the orbit laterally and anterior cranial fossa
superiorly. It has 4 main parts: the perpendicular plate, cribriform plate, and 2
ethmoidal labyrinths.Other prominent structures include the uncinate process, middle
turbinate, superior turbinate, and crista galli.
References: Michael Schunke, ES. PROMETHEUS LernAtras der Anatomie. First
Japanease edition ed. 2009: Thieme.
This exhibit illustrates the radiological normal anatomy and variants of the ethmoid bone
from an embryological point of view, specifically addressing the 5 basal-lamellae concept
and migration of air cells.
Page 4 of 74
Images for this section:
Fig. 1: Ethmoid bone. The ethmoid bone is a cuboidal structure with some prominences,
forming the boundary of the orbit laterally and anterior cranial fossa superiorly. It has
4 main parts: the perpendicular plate, cribriform plate, and 2 ethmoidal labyrinths.Other
prominent structures include the uncinate process, middle turbinate, superior turbinate,
and crista galli.
Page 5 of 74
Imaging findings OR Procedure details
I. Embryology
A. Embryology
Ethmoturbinals, the origin of the basal lamellae, arise at the lateral wall of the nasal
cavity. Development continues up to the seventh month of the gestation with regression
thereafter until birth. Four to 5 ethmoturbinals eventually remain as the uncinate process,
ethmoid bulla, middle turbinate, superior turbinate, and supreme turbinate (Fig 2)[1]. The
ethmoturbinal is divided into an ascending portion, descending portion, and genu, which
is angle between ascending and descending portions. The nasal meatus is similarly
divided into the ascending and descending portions and the genu (Figs 3, 4)[2].
The ascending portion of the middle meatus (or recessus superior) develops into the
hiatus semilunaris and frontal sinus. The descending portion (or recessus inferior)
develops into infundibulum and the maxillary sinus (Fig 3)[3]. Development of the
ascending portion is rudimentary, except for the middle turbinate and middle meatus. The
ethmoid air cells develop from the descending portion.
Fig. 2: Lateral aspect of nasal cavity. This schematic diagram (a) shows 5
ethmoturbinals which develop into 1) the uncinate process, 2) ethmoid bulla, 3) middle
turbinate, 4) superior turbinate, and 5) supreme turbinate (b).
References: Howard Levine, MC. Sinus Surgery: Endoscopic and Microscopic
Approaches. 2004: Thieme. Michael Schunke, ES. PROMETHEUS LernAtras der
Anatomie. First Japanease edition ed. 2009: Thieme.
Page 6 of 74
Fig. 3: Coronal section of the nasal sinus, 12 weeks gestation. Ascending portion of
the middle meatus (*) develops into frontal recess and frontal sinus. The descending
portion (**) develops into infundibulum and maxillary sinus. (Uncinate process [UP],
ethmoid bulla [EB], middle turbinate [MT])
References: Mizukoshi, O. Clinical Otorhinolaryngology and Head and Neck Surgery.
Vol. 6A. 1989.
Page 7 of 74
Fig. 4: Ascending and descending portions of the middle turbinate, lateral aspect
of nasal cavity, and coronal section. Ethmoturbinal is divided into lamina basilaris
(red dotted line) and lamina recurvata (blue line). The lamina basilaris forms part
of the lateral wall attachment. The lamina recurvata is more medial with a curled
configuration. The lamina basilaris separates the draining pathway. The genu is the
angle between the ascending and descending portions (yellow line). The other portion
of ethmoturbinals show similar development.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
B. The 5 basal-lamellae concept
Seydel divided the ethmoturbinals into "Basallamelle" and "Einrollungen", which are
named as the lamina basilaris (basal lamellae) and lamina recurvata by Killian,
respectively (Fig 4)[4]. The lamina basilaris forms part of the attachment of the
ethmoturbinals to the lateral wall of the nasal cavity. The lamina recurvata is a medially
protruding structure with a rolling configuration. The uncinate process and ethmoid bulla
are mainly derived from the basal lamella and lamina recurvata does not develop well [1].
In addition to the middle and superior turbinates, the uncinate process and ethmoid bulla
are derived from the ethmoturbinals, leading Killian to establish the concept of at least 4
basal lamellae, 5 if the supreme turbinate is included [5]. The basal lamellae demarcate
the anatomical pathways of sinus drainage.
C. Ethmoid anatomy from an embryological point of view
Ethmoid air cells can grow in any direction and invade adjacent bones [6]. This migration
of ethmoid cells, in addition to the 5 basal-lamellae concept, is the key to understanding
ethmoid anatomy.
The first basal lamella develops into the uncinate process and the agger nasi cells,
derived from pneumatization of the anterior portion of the first basal lamella. The second
basal lamella is also pneumatized and is called the ethmoid bulla. The frontal recess
and ethmoid infundibulum open into the middle meatus between the uncinate process
(the first basal lamella) and ethmoid bulla (the second basal lamella). The embryology
of the ostiomeatal complex explains its anatomy. The frontal sinus and maxillary sinus
originate from the ascending and descending portions of nasal meatus, which continue
to the middle meatus between the first and second basal lamellae (Fig 3). The ethmoid
bulla drains into the hiatus semilunaris superior located between the second and third
basal lamellae. The third basal lamella divides ethmoid air cells into anterior and posterior
ethmoid cells, and the fourth basal lamella separates posterior ethmoid air cells into
posterior and postreme cells (Fig 5).
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Fig. 5: Ethmoid anatomy: The 5 basal-lamellae concept. The basal lamellae (blue
arrows) separate the draining pathways (red arrows). The frontal and maxillary sinuses
drain into the middle meatus via the frontal recess and hiatus semilunaris between
the first (agger nasi cells and uncinate process) and second (ethmoid bulla) basal
lamellae. The hiatus semilunaris superior opens between the second and third lamellae
(middle turbinate). The third basal lamella separates the anterior and posterior ethmoid
cells. The fourth basal lamella (superior turbinate) divides the posterior and postreme
meatus.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
Pneumatization around the ethmoid bulla is called the suprabullar cells, frontal bullar
cells, and sinus lateralis (suprabullar recess and retrobullar recess). The infraorbital, or
Haller, cells and supraorbital ethmoid cells represent invasive pneumatization of the floor
or roof of orbit respectively. Anterior ethmoid cells may invade the interfrontal sinus septa
and crista galli, and posterior air cells may extend to the turbinate (concha bullosa) or
above the sphenoid sinus (Onodi cells) (Fig 6).
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The ethmoid air cells are classified into intramural and extramural based on migration into
or out of the ethmoid bone. Extramural cells contain Haller cells, frontal cells, supraorbital
ethmoid cells, interfrontal sinus septal cell, and Onodi cells [6, 7].
Fig. 6: Migration of ethmoid cells. Agger nasi cells (AN) and ethmoid bulla (EB)
are derived from pneumatization of the first and second basal lamellae. Agger nasi
cells are the most anterior air cells and can invade uncinate process. The frontal
cells, located above the agger nasi cells, form the anterior wall of the frontal recess.
Additional anterior ethmoid cells are located around the ethmoid bulla (suprabullar
recess, suprabullar cells, frontal bullar cells, and retrobullar recess) or orbital wall
(supraorbital ethmoid cells, and Haller cells). Anterior ethmoid cells can extend to
interfrontal sinus septa and crista galli. Posteriorly, they may extend to the turbinate
(concha bullosa) or above the sphenoid sinus (Onodi cells). (Air cells around agger
nasi cells [blue], ethmoid bulla [red], posterior air cells [yellow])
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
II. Bone anatomy and variants
A. Bone anatomy and variants derived from the 5 basal lamellae
1. Uncinate process and agger nasi cells
a) Uncinate process
The uncinate process is derived from the first basal lamella. It forms the boundaries of
the hiatus semilunaris and the ethmoid infundibulum. The uncinate process has many
anatomical variants, some of which may obstruct the ethmoid infundibulum:
Page 10 of 74
•
•
•
Medially bent uncinate process may cause obstruction because of contact
with the middle turbinate (Fig 7).
Elongated or enlarged uncinate process (Fig 8)
Pneumatized uncinate process believed to represent an extension of agger
nasi cells (Fig 9) [8].
Fig. 7: Medially bent uncinate process. The uncinate process is bent
medially, contacting the middle turbinate and occluding the infundibulum
(red arrow). Mucus drains through the accessory foramen (yellow arrow). In
this case, mucosal thickening is caused by dental caries (blue arrow).
References: Department of Radiology, University of Tsukuba - Tsukuba,
Ibaraki/JP
Page 11 of 74
Fig. 8: Elongated or enlarged uncinate processes. This patient presented
with left maxillary sinusitis. An elongated or enlarged uncinate process (red
arrow in b) was found after cleaning of the nasal cavity.
References: Department of Radiology, University of Tsukuba - Tsukuba,
Ibaraki/JP
Fig. 9: Pneumatized uncinate process. Pneumatized uncinate process (red
arrow) is believed to represent extension of agger nasi cells. In this case, the
agger nasi cell extends to the uncinate process (yellow arrow, c).
References: Department of Radiology, University of Tsukuba - Tsukuba,
Ibaraki/JP
Attachment variants
Page 12 of 74
Attachment of the uncinate process is important for surgery and sinus pathology, as it
allows determination of whether the frontal sinus drains into or laterally to the ethmoid
infundibulum.
The uncinate process may be attached to:
•
•
•
Lamina papyracea or agger nasi (lamina terminalis). The frontal recess
opens directly into middle meatus. The lamina terminalis is the blind pouch
between the uncinate process and lamina papyracea (Figs 10a,b)[9].
Skull base or middle turbinate. The frontal recess drains into the ethmoid
infundibulum (Figs 10c, d, 11)[9].
Orbital floor or inferior aspect of the lamina papyracea (silent sinus
syndrome, atelectatic uncinate process). This variant is associated
with hypoplastic, ipsilateral maxillary sinus secondary to closure of the
infundibulum. Enophthalmos may result from the inferior retraction of the
orbital wall [8].
Page 13 of 74
Fig. 10: Four different attachments of the uncinate process. When the
uncinate process attaches to ethmoid bulla or lamina papyracea (red arrows,
a and b), the frontal recess opens directly into middle meatus. When the
attachment is at the skull base or middle turbinate (red arrows, c and d), the
frontal recess opens into the ethmoid infundibulum. Yellow dotted line shows
drainage pathway. (Lamina terminalis (*))
References: Department of Radiology, University of Tsukuba - Tsukuba,
Ibaraki/JP
Page 14 of 74
Fig. 11: Uncinate process attachment to the middle turbinate (red arrows).
Anterior to posterior coronal CT images of the same patient as Fig 10d. In
this condition, frontal recess opens into the ethmoid infundibulum.(yellow
dots).
References: Department of Radiology, University of Tsukuba - Tsukuba,
Ibaraki/JP
b) Agger nasi cells
The agger nasi cells, from the Latin agger meaning small mound, are the most anterior
air cells (Fig 12). They are derived from pneumatization of the anterior part of the first
basal lamella [8]. The agger nasi cells are located anterior to the uncinate process and
Page 15 of 74
posteromedial to the lacrimal sac (Fig 12d) and may invade the lacrimal bone. The agger
nasi is an important surgical landmark.
Fig. 12: Agger nasi cells. Agger nasi cells (green arrows) are the most anterior of
the ethmoid cells. The agger nasi cells drain to the middle nasal meatus (orange
arrows).The agger nasi cells are located posteromedial to the lacrimal sac and are the
anatomical landmark for this sac during surgery.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
2. Ethmoid bulla
Page 16 of 74
The ethmoid bulla is derived from pneumatization of the second basal lamella (Fig 13).
It lacks a distinct posterior wall and therefore is not a separate cell but rather a bony
lamella with an air space behind it [10]. The ethmoid bulla is the largest and most
consistent anterior ethmoid cell, and constitutes a reliable anatomical landmark. The
degree of pneumatization is variable. Giant ethmoid bulla may cause obstruction of the
ostiomeatal complex. The term torus lateralis designates the second basal lamella that
is not pneumatized (Fig 14)[11].
Fig. 13: Ethmoid bulla. The ethmoid bulla (EB) is located in the anterior air cells and
is usually the largest cell. EB is formed by pneumatization of the second basal lamella.
(Agger nasi cell [AN], uncinate process [UP], sinus lateralis [SL], frontal recess [FR])
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
Page 17 of 74
Fig. 14: Torus lateralis. The torus lateralis (green arrows) represents an ethmoid bulla
without pnenumatization. (Agger nasi cell [AN])
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
3. Middle turbinate
The middle turbinate, derived from the third lamella, separates the ethmoid cells into
the anterior and posterior ethmoid cells. The anterior ethmoid cells drain into the middle
meatus, while the posterior ethmoid cells drain into the superior meatus. The insertion
of the middle turbinate can be divided into 3 parts. The first or vertical part lies in the
anterior one-third of the middle turbinate, oriented in the sagittal plane. In this part, the
middle turbinate attaches to the cribriform plate. The second or oblique part attaches to
the basal lamella or lamina papyracea. The third or horizontal part lies horizontally in the
posterior one-third of the middle turbinate. In this part, the middle turbinate attaches to
the perpendicular plate of the palatine bone (Fig 15). These attachments provide stability
to the middle turbinate. The middle turbinate has many variants.
•
•
•
Concha bullosa:
This aerated turbinate may be the site of inflammatory processes ranging
from simple mucosal thickening to a mucocele (Fig 16)[12].
Paradoxical middle turbinate:
A paradoxical middle turbinate is formed by the inverse curling of the middle
turbinate. This variant is not associated with sinus pathology (Fig 17a)[13].
Turbinate sinus:
A curved middle turbinate may curl upon itself to form an internal concavity,
called a turbinate sinus (Fig 17b).
Other variants include medial and lateral displacement, lateral bending, L-shaped
configuration, and sagittal transverse clefts [14].
Page 18 of 74
Fig. 15: Attachment of the middle turbinate. The insertion of the middle turbinate
can be divided into 3 parts. The first or vertical part attaches to the cribriform plate.
The second or oblique part attaches to the basal lamella or lamina papyracea. The
third or horizontal part attaches to the perpendicular plate of the palatine bone. These
attachments help to stabilize the middle turbinate.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
Page 19 of 74
Fig. 16: Concha bullosa. Concha bullosa of the middle turbinate in 2 different patients.
Concha bullosa in patient 1 showing pneumatization of the middle turbinate (a, b).
Concha bullosa may be the site of inflammatory disease ranging from simple mucosal
thickening to mucocele (c, d).
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
Page 20 of 74
Fig. 17: Paradoxical middle turbinate (a) and turbinate sinus (b). Paradoxical middle
turbinate is formed by the inverse curling of middle turbinate and direct lateral convexity
of the bone toward the lateral sinus wall. Turbinate sinus (red arrows, b) is formed by
the concavity of the curled segment.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
4. Superior turbinate
The superior turbinate is derived from the fourth lamella. Concha bullosa may coexist
and cause headache (Fig 18) [15].
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Fig. 18: Concha bullosa of the superior turbinate. Concha bullosa may occur in the
superior turbinate, a structure derived from the fourth lamella. This variant may cause
headache.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
5. Supreme turbinate
The supreme turbinate is usually rudimentary.
B. Bone anatomy and variants derived from other important structures
1. Ethmoid roof
Page 22 of 74
The ethmoid roof protects the anterior cranial fossa during surgery. It consists of fovea,
crista galli, lateral lamella, and cribriform plate (Fig 19). Foveal angle, measured between
the fovea and the lamina papyracea, is an index for determining the risk of operation
(Fig 20a, b). A low-sloping fovea predisposes to a risk of anterior cranial penetration.
Asymmetry of the ethmoid roof also increases the risk of penetration into the anterior
cranial fossa (Fig 20c).
The lateral lamella is one of the critical structures for surgery. The depth of the olfactory
pit was classified by Kero as follows (Fig 21) [16]:
Type 1: 1-3 mm
Type 2: 4-7 mm
Type 3: 8-16 mm
The cribriform plate and lateral lamella are thin structures that are easily broken.
Dehiscence or congenital defect may also occur, associated with spontaneous
cerebrospinal fluid rhinorrhea (Fig 22) [17].
Fig. 19: Ethmoid roof. The ethmoid roof consists of fovea, crista galli, lateral lamella,
and cribriform plate. Cribriform plate is a thin structure that may be dehiscent or
defective.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
Page 23 of 74
Fig. 20: Foveal angle (a, b) and asymmetry of the ethmoid roof (c). Foveal angle is the
angle between the fovea and lamina papyracea. A low sloping fovea predisposes to
anterior cranial penetration during surgery. Differences in height between the right and
left fovea are also significant for surgery. The ethmoid roof is lower and high sloping on
the right side (arrow)
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
Page 24 of 74
Fig. 21: Kero's classification: Type 1 (a), Type 2 (b), and Type3 (c). Kero's
classification is based on the depth of the olfactory pit. In the type 3 in particular,
the ethmoid roof is significantly higher than the anterior cranial fossa, increasing the
surgical risk.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
Page 25 of 74
Fig. 22: Spontaneous cerebral fluid leakage from the left cribriform plate. Cribriform
plate calcification is obscure on the left side (a). STIR sequences show fluid continuous
to the subarachnoid space (red arrow, b).
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
2. Lamina papyracea
The lamina papyracea is a thin structure in which dehiscence may be seen, most often at
the insertion of the basal lamella (Fig 23)[18]. Associated bulging of the orbital contents
poses a risk for surgery.
Fig. 23: Dehiscence of the lamina papyracea with medial herniation of orbital fat. Bony
dehiscence occurs most often at the insertion of the basal lamella.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
Page 26 of 74
3. Ethmoid foramen
Injury to the anterior ethmoidal artery during endoscopic procedures may cause
intracranial or orbital hematoma, and preoperative assessment of this artery is essential
to avoid complications. The ethmoid artery runs through the ethmoid foramen. The
ethmoid foramen may be located using the medial notch of the orbit and anterior
ethmoidal sulcus as a landmark on the CT images (Fig 24)[19]. Injury to the posterior
ethmoid artery, located 10-12 mm behind anterior ethmoid foramen, is less common.
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Fig. 24: Anterior and posterior ethmoid foramina. The medial notch of the orbit is a
useful landmark for identifying the ethmoid foramen. The posterior ethmoid artery is
located 10-12 mm behind anterior ethmoid foramen.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
III. Air cell anatomy and variants
The ethmoid sinuses arise from the endochondral bone. This origin results in remarkably
thin bony contours with irregular and morphologically unique borders [6]. Pneumatization
is variable, limited only by the presence of hard bone.
A. Anterior ethmoid air cells
1. Intramural cells
a) Sinus lateralis (the lateral sinus of Grunwald, suprabullar recess, and retrobullar
recess)
The sinus lateralis, also called the suprabullar or retrobullar recesses, is located superior
and posterior to the ethmoid bulla (Fig 25). The sinus lateralis can extend dorsally, far
posterior and inferior between the ethmoid bulla and the basal lamella of the middle
turbinate, opening into a space known as the hiatus semilunaris superior. The ethmoid
bulla usually opens into a well-pneumatized sinus lateralis. If the ethmoid bulla does not
extend to the skull base, the sinus lateralis may continue anteriorly into the frontal recess
(Fig 25c)[20]. The suprabullar and retrobullar recesses can also be approached medially
and inferiorly through the hiatus semilunaris superior.
Page 28 of 74
Fig. 25: Sinus lateralis (the lateral sinus of Grunwald, suprabullar recess, and
retrobullar recess). The sinus lateralis(retrobullar recess, red dotted line, b-d) is the
space between the ethmoid bulla (EB) and the third basal lamella (yellow dotted line).
When ethmoid bulla dose not extend to the roof, the sinus lateralis continues to frontal
recess (suprabullar recess, blue dotted line, c). The ethmoid bulla opens posteriorly
into lateral recess (** in b). (Agger nasi cell [AN],suprabullar cell [*])
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
b) Suprabullar cells and frontal bullar cells
The suprabullar and frontal bullar cells are located above the ethmoid bulla (Figs 26, 27).
The suprabullar cells do not protrude into the frontal sinus, in contrast to the frontal bullar
cells, which extend to the frontal sinus. The frontal recess may be narrow between the
agger nasi and suprabullar or frontal bullar cells. The suprabullar and frontal cells are
equivalent to the suprabullar recess, which appears as a cleft above the ethmoid bulla
Page 29 of 74
during endoscopy. The prevalence of suprabullar and frontal cells is approximately 8%
and 10%, respectively [21].
Fig. 26: Suprabullar and frontal bullar cells. Suprabullar cells (Fig a, b *) do not extend
to the frontal sinus in contrast to frontal bullar cells (Fig c, d **). The frontal recess may
be narrow between the agger nasi cells (AN) and suprabullar or frontal bullar cells (b).
(Ethmoid bulla [EB])
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
Page 30 of 74
Fig. 27: Inflammation of the frontal bullar cells. Frontal bullar cells are opacified (*).
The frontal sinus is clear because the frontal recess is not involved.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
c) Pneumatization of the crista galli
Pneumatization of the crista galli may communicate with the frontal recess (Fig 28).
Obstruction of ostium causes chronic sinusitis or mucocele formation within the crista
galli [22]. Recognition of this variant is important to avoid extension into anterior cranial
fossa during surgery.
Page 31 of 74
Fig. 28: Pneumatization of the crista galli. Anterior ethmoid cells extending to the crista
galli.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
2. Extramural cells
a) Haller cells#infraorbital cells#
Page 32 of 74
Haller cells, first identified by Haller in 1765, extend to the medial roof of the
maxillary sinus, inserted between the lamina papyracea and the uncinate process
below the ethmoid bulla (Fig 29). Haller cells may contribute to the narrowing of the
infundibulum[23].
Fig. 29: Haller cells. Haller cells (red arrow) are located at the medial floor of
the maxillary sinus below the ethmoid bulla (EB). When small, they may be
similar appearance to the infraorbital canal (c, d). Due to their location next to the
infundibulum, Haller cells may obstruct sinus drainage. (Uncinate process [*] posterior
ethmoid cell [PC] Infraorbital canal [yellow arrow])
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
Page 33 of 74
b) Frontal cells
Frontal cells are anterior ethmoid cells located above the agger nasi cells that may
obstruct the frontal recess. Bent and Kuhn classify frontal cells into 4 different types (Fig
30)[21, 24].
Type 1: Single cell, not extending into the frontal sinus (24.2%)
Type 2: Two or more cells, sometimes extending to the inferior
frontal sinus (4.2%)
Type 3: Single cell, extending into the frontal sinus (3.1%)
Type 4: Isolated cells located in the frontal sinus (0.0%)
Fig. 30: Frontal cells: Type 1 (a, b), Type 2 (c, d), and Type 3 (e, f). Frontal cells (*)
are located above the agger nasi cells (AN). Frontal cells form the anterior wall of
the drainage pathway from the frontal sinus (yellow dotted line), and encroach on the
frontal recess or frontal sinus.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
c) Supraorbital ethmoid cell
Page 34 of 74
The supraorbital ethmoid cell extends behind the frontal sinus through the orbital plate of
the frontal bone (Fig 31). It simulates a septated frontal sinus (Fig 32). The supraorbital
ethmoid cell can compromise frontal sinus drainage. During endoscopic surgery, it may
be mistaken for the frontal sinus.
Fig. 31: Supraorbital ethmoid cells. The supraorbital ethmoid cell (*) extend to the
orbital plate of the frontal bone. The anterior ethmoid foramen (red arrows) is easily
identified by pneumatization of the supraorbital ethmoid cell.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
Page 35 of 74
Fig. 32: Mucocele of the supraorbital ethmoid cell. Left ethmoid mucocele (*) is bulging
into orbital fossa. On the axial slices of the CT (b, c), supraorbital cell (*) are easily
mistaken for frontal sinus (**). In this case frontal sinus and frontal recess (yellow
dotted line and red arrow) are intact.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
d) Interfrontal sinus septal cell
The interfrontal sinus septal cell is located in the interfrontal septa (Fig 33). This variant
may cause inflammation and mucocele [14].
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Fig. 33: Interfrontal sinus septal cell. The interfrontal sinus septal cell (*) is located
between the frontal sinuses. This cell drains into frontal recess (red dotted line).
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
B. Posterior ethmoid air cells
1. Intramural cells
a) Posterior, postreme ethmoid cells
Posterior and postreme ethmoid cells drain into the superior meatus and may extend
above the maxillary sinus (Fig 34). The fourth basal lamella divides the posterior ethmoid
group of cells into posterior and postreme ethmoid cells.
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Fig. 34: Posterior ethmoid cell (PC) and postreme ethmoid cell (PSC) The superior
nasal turbinate (fourth basal lamella; yellow arrows in a, b) separates the posterior and
postreme ethmoid cells. Posterior ethmoid cell can invade into the roof of the maxillary
sinus behind the Haller cell (c, d).
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
2. Extramural cells
a) Onodi cells (sphenoethmoidal cells)
Onodi cells, also known as sphenoethmoidal cells, are postreme ethmoid cells which
extend above the sphenoid sinus (Fig 35). Onodi cells are intimately related to the optic
nerve and internal carotid artery. Onodi cells could be mistaken for the sphenoid sinus
during endoscopic surgery. Mucocele or fungal sinusitis of Onodi cells may cause visual
disturbance (Fig 36).
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Fig. 35: Onodi cells. Onodi cells (OC), or sphenoethmoidal cells, represent invasion of
the postreme ethmoid cells above the sphenoid sinus. These cells can contact the optic
nerve (a, b) and internal carotid artery(c). Pneumatization may extend to the anterior
clinoid process (*).
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
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Fig. 36: Aspergillosis of the Onodi cell. Aspergillosis of the Onodi cell in a 60-yearold man with right visual disturbance. Right Onodi cell (*) invades the anterior clinoid
process, with local inflammation (yellow arrows) involving the right optic nerve. As part
of the ethmoid sinus, this structure should not be confused with the sphenoid sinus (**).
Aspergillus was identified in the specimen postsurgery.
References: Department of Radiology, University of Tsukuba - Tsukuba, Ibaraki/JP
Images for this section:
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Fig. 2: Lateral aspect of nasal cavity. This schematic diagram (a) shows 5 ethmoturbinals
which develop into 1) the uncinate process, 2) ethmoid bulla, 3) middle turbinate, 4)
superior turbinate, and 5) supreme turbinate (b).
Fig. 3: Coronal section of the nasal sinus, 12 weeks gestation. Ascending portion of the
middle meatus (*) develops into frontal recess and frontal sinus. The descending portion
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(**) develops into infundibulum and maxillary sinus. (Uncinate process [UP], ethmoid
bulla [EB], middle turbinate [MT])
Fig. 4: Ascending and descending portions of the middle turbinate, lateral aspect of nasal
cavity, and coronal section. Ethmoturbinal is divided into lamina basilaris (red dotted
line) and lamina recurvata (blue line). The lamina basilaris forms part of the lateral wall
attachment. The lamina recurvata is more medial with a curled configuration. The lamina
basilaris separates the draining pathway. The genu is the angle between the ascending
and descending portions (yellow line). The other portion of ethmoturbinals show similar
development.
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Fig. 5: Ethmoid anatomy: The 5 basal-lamellae concept. The basal lamellae (blue arrows)
separate the draining pathways (red arrows). The frontal and maxillary sinuses drain into
the middle meatus via the frontal recess and hiatus semilunaris between the first (agger
nasi cells and uncinate process) and second (ethmoid bulla) basal lamellae. The hiatus
semilunaris superior opens between the second and third lamellae (middle turbinate).
The third basal lamella separates the anterior and posterior ethmoid cells. The fourth
basal lamella (superior turbinate) divides the posterior and postreme meatus.
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Fig. 6: Migration of ethmoid cells. Agger nasi cells (AN) and ethmoid bulla (EB) are
derived from pneumatization of the first and second basal lamellae. Agger nasi cells are
the most anterior air cells and can invade uncinate process. The frontal cells, located
above the agger nasi cells, form the anterior wall of the frontal recess. Additional anterior
ethmoid cells are located around the ethmoid bulla (suprabullar recess, suprabullar cells,
frontal bullar cells, and retrobullar recess) or orbital wall (supraorbital ethmoid cells, and
Haller cells). Anterior ethmoid cells can extend to interfrontal sinus septa and crista galli.
Posteriorly, they may extend to the turbinate (concha bullosa) or above the sphenoid
sinus (Onodi cells). (Air cells around agger nasi cells [blue], ethmoid bulla [red], posterior
air cells [yellow])
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Fig. 7: Medially bent uncinate process. The uncinate process is bent medially, contacting
the middle turbinate and occluding the infundibulum (red arrow). Mucus drains through
the accessory foramen (yellow arrow). In this case, mucosal thickening is caused by
dental caries (blue arrow).
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Fig. 8: Elongated or enlarged uncinate processes. This patient presented with left
maxillary sinusitis. An elongated or enlarged uncinate process (red arrow in b) was found
after cleaning of the nasal cavity.
Fig. 9: Pneumatized uncinate process. Pneumatized uncinate process (red arrow) is
believed to represent extension of agger nasi cells. In this case, the agger nasi cell
extends to the uncinate process (yellow arrow, c).
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Fig. 10: Four different attachments of the uncinate process. When the uncinate process
attaches to ethmoid bulla or lamina papyracea (red arrows, a and b), the frontal recess
opens directly into middle meatus. When the attachment is at the skull base or middle
turbinate (red arrows, c and d), the frontal recess opens into the ethmoid infundibulum.
Yellow dotted line shows drainage pathway. (Lamina terminalis (*))
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Fig. 11: Uncinate process attachment to the middle turbinate (red arrows). Anterior to
posterior coronal CT images of the same patient as Fig 10d. In this condition, frontal
recess opens into the ethmoid infundibulum.(yellow dots).
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Fig. 12: Agger nasi cells. Agger nasi cells (green arrows) are the most anterior of the
ethmoid cells. The agger nasi cells drain to the middle nasal meatus (orange arrows).The
agger nasi cells are located posteromedial to the lacrimal sac and are the anatomical
landmark for this sac during surgery.
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Fig. 13: Ethmoid bulla. The ethmoid bulla (EB) is located in the anterior air cells and
is usually the largest cell. EB is formed by pneumatization of the second basal lamella.
(Agger nasi cell [AN], uncinate process [UP], sinus lateralis [SL], frontal recess [FR])
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Fig. 14: Torus lateralis. The torus lateralis (green arrows) represents an ethmoid bulla
without pnenumatization. (Agger nasi cell [AN])
Fig. 15: Attachment of the middle turbinate. The insertion of the middle turbinate can be
divided into 3 parts. The first or vertical part attaches to the cribriform plate. The second
or oblique part attaches to the basal lamella or lamina papyracea. The third or horizontal
part attaches to the perpendicular plate of the palatine bone. These attachments help to
stabilize the middle turbinate.
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Fig. 16: Concha bullosa. Concha bullosa of the middle turbinate in 2 different patients.
Concha bullosa in patient 1 showing pneumatization of the middle turbinate (a, b). Concha
bullosa may be the site of inflammatory disease ranging from simple mucosal thickening
to mucocele (c, d).
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Fig. 17: Paradoxical middle turbinate (a) and turbinate sinus (b). Paradoxical middle
turbinate is formed by the inverse curling of middle turbinate and direct lateral convexity
of the bone toward the lateral sinus wall. Turbinate sinus (red arrows, b) is formed by the
concavity of the curled segment.
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Fig. 18: Concha bullosa of the superior turbinate. Concha bullosa may occur in the
superior turbinate, a structure derived from the fourth lamella. This variant may cause
headache.
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Fig. 19: Ethmoid roof. The ethmoid roof consists of fovea, crista galli, lateral lamella, and
cribriform plate. Cribriform plate is a thin structure that may be dehiscent or defective.
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Fig. 20: Foveal angle (a, b) and asymmetry of the ethmoid roof (c). Foveal angle is
the angle between the fovea and lamina papyracea. A low sloping fovea predisposes to
anterior cranial penetration during surgery. Differences in height between the right and
left fovea are also significant for surgery. The ethmoid roof is lower and high sloping on
the right side (arrow)
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Fig. 21: Kero's classification: Type 1 (a), Type 2 (b), and Type3 (c). Kero's classification
is based on the depth of the olfactory pit. In the type 3 in particular, the ethmoid roof is
significantly higher than the anterior cranial fossa, increasing the surgical risk.
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Fig. 22: Spontaneous cerebral fluid leakage from the left cribriform plate. Cribriform plate
calcification is obscure on the left side (a). STIR sequences show fluid continuous to the
subarachnoid space (red arrow, b).
Fig. 23: Dehiscence of the lamina papyracea with medial herniation of orbital fat. Bony
dehiscence occurs most often at the insertion of the basal lamella.
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Fig. 24: Anterior and posterior ethmoid foramina. The medial notch of the orbit is a useful
landmark for identifying the ethmoid foramen. The posterior ethmoid artery is located
10-12 mm behind anterior ethmoid foramen.
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Fig. 25: Sinus lateralis (the lateral sinus of Grunwald, suprabullar recess, and retrobullar
recess). The sinus lateralis(retrobullar recess, red dotted line, b-d) is the space between
the ethmoid bulla (EB) and the third basal lamella (yellow dotted line). When ethmoid bulla
dose not extend to the roof, the sinus lateralis continues to frontal recess (suprabullar
recess, blue dotted line, c). The ethmoid bulla opens posteriorly into lateral recess (** in
b). (Agger nasi cell [AN],suprabullar cell [*])
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Fig. 26: Suprabullar and frontal bullar cells. Suprabullar cells (Fig a, b *) do not extend
to the frontal sinus in contrast to frontal bullar cells (Fig c, d **). The frontal recess may
be narrow between the agger nasi cells (AN) and suprabullar or frontal bullar cells (b).
(Ethmoid bulla [EB])
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Fig. 27: Inflammation of the frontal bullar cells. Frontal bullar cells are opacified (*). The
frontal sinus is clear because the frontal recess is not involved.
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Fig. 28: Pneumatization of the crista galli. Anterior ethmoid cells extending to the crista
galli.
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Fig. 29: Haller cells. Haller cells (red arrow) are located at the medial floor of the maxillary
sinus below the ethmoid bulla (EB). When small, they may be similar appearance to
the infraorbital canal (c, d). Due to their location next to the infundibulum, Haller cells
may obstruct sinus drainage. (Uncinate process [*] posterior ethmoid cell [PC] Infraorbital
canal [yellow arrow])
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Fig. 30: Frontal cells: Type 1 (a, b), Type 2 (c, d), and Type 3 (e, f). Frontal cells (*)
are located above the agger nasi cells (AN). Frontal cells form the anterior wall of the
drainage pathway from the frontal sinus (yellow dotted line), and encroach on the frontal
recess or frontal sinus.
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Fig. 31: Supraorbital ethmoid cells. The supraorbital ethmoid cell (*) extend to the orbital
plate of the frontal bone. The anterior ethmoid foramen (red arrows) is easily identified
by pneumatization of the supraorbital ethmoid cell.
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Fig. 32: Mucocele of the supraorbital ethmoid cell. Left ethmoid mucocele (*) is bulging
into orbital fossa. On the axial slices of the CT (b, c), supraorbital cell (*) are easily
mistaken for frontal sinus (**). In this case frontal sinus and frontal recess (yellow dotted
line and red arrow) are intact.
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Fig. 33: Interfrontal sinus septal cell. The interfrontal sinus septal cell (*) is located
between the frontal sinuses. This cell drains into frontal recess (red dotted line).
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Fig. 34: Posterior ethmoid cell (PC) and postreme ethmoid cell (PSC) The superior
nasal turbinate (fourth basal lamella; yellow arrows in a, b) separates the posterior and
postreme ethmoid cells. Posterior ethmoid cell can invade into the roof of the maxillary
sinus behind the Haller cell (c, d).
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Fig. 35: Onodi cells. Onodi cells (OC), or sphenoethmoidal cells, represent invasion of
the postreme ethmoid cells above the sphenoid sinus. These cells can contact the optic
nerve (a, b) and internal carotid artery(c). Pneumatization may extend to the anterior
clinoid process (*).
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Fig. 36: Aspergillosis of the Onodi cell. Aspergillosis of the Onodi cell in a 60-year-old man
with right visual disturbance. Right Onodi cell (*) invades the anterior clinoid process, with
local inflammation (yellow arrows) involving the right optic nerve. As part of the ethmoid
sinus, this structure should not be confused with the sphenoid sinus (**). Aspergillus was
identified in the specimen postsurgery.
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Conclusion
Knowledge of anatomical variants of the ethmoid bone is necessary for the diagnosis
of paranasal abnormalities and endoscopic treatment planning. An understanding of
ethmoid bone embryology facilitates recognition of anatomical structures and normal
variants in this area.
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Personal Information
Thank you for reading our poster.
If you have any questions or opinions, please contact me by email.
Takashi Hiyama, M.D.
Department of Radiology, University of Tsukuba Hospital
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E-mail: [email protected]
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