Introduction
Anterior skull base meningiomas account for 40% of all intracranial meningiomas. Half
of these meningiomas are sphenoid wing meningiomas, including a subcategory named
anterior clinoid meningiomas.[1 ] Among anterior skull base meningiomas, 15% are midline suprasellar meningiomas,
which start very anteriorly as olfactory groove meningiomas, followed by planum sphenoidale,
tuberculum sellae, and, most posteriorly, diaphragma sellae meningiomas.
Most midline suprasellar meningiomas affect vision. These types of meningiomas show
rapid and worse visual deterioration before reaching a size that may affect the intracranial
pressure. This rapid deterioration is attributed to compression of the optic chiasm
and/or extension of the tumor toward the optic canal, and compression of the optic
nerves within the narrow canal, which may cause acute or subacute blindness.[2 ]
[3 ]
Multiple attempts have been made to classify suprasellar meningiomas. These classifications
were based on the patency of the anterior intercavernous sinus, bone expansion, and
involvement of diaphragma sellae. Recently, different ratios and tumor extension parameters
have also been used to distinguish suprasellar meningiomas, but no clinical significance
was ascertained.[4 ]
[5 ] In the past few years, we have encountered an increasing number of cases that did
not fit these classifications. In addition, obtaining bony measurements and preoperative
ratios is difficult. Therefore, we aimed to classify suprasellar meningiomas based
on their site of origin and behaviors toward the underlying bone and neurovascular
structure displacement.
Methods
Data from suprasellar meningiomas that were operated using the extended endoscopic
transnasal approach (EETA) between 2015 and 2021 were collected. Electronic files
and images were reviewed for all the cases. All newly diagnosed cases of midline suprasellar
meningioma were included. Parasellar meningiomas and cases with a history of complete
or partial resection through craniotomy that underwent a second surgery through EETA
were excluded. Additionally, olfactory groove meningiomas were excluded from the data
because of their remote location in the optic chiasm.
Demographic data including age, sex, and presenting symptoms were collected. Visual
affection was analyzed as unilateral, bilateral, symmetrical, asymmetrical, and duration
of visual complaints. Hormonal assessments were reviewed as well.
Preoperative images were reviewed, and computed tomography (CT) thin-cut scans were
evaluated for a detailed bony anatomy of the area ([Fig. 1A, C ]). The planum sphenoidale was identified as the flat area posterior to the cribriform
plate and crista galli. The chiasmatic sulcus is the groove posterior to the planum
sphenoidale that houses the optic chiasm. Tuberculum sellae was defined as the most
posterior ridge of the anterior wall of the sellae. The diaphragma sella constitute
the two dura leaves that extend from the tuberculum sella over the sella turcica to
the dorsum sellae. In midsagittal CT scans of the bone window, the distance from the
tuberculum sellae to the most posterior bony ridge of the planum sphenoidale was measured
in millimeters and defined as sulcal length or the length of the chiasmatic sulcus
([Fig. 2C ]).
Fig. 1 Suprasellar anatomy. (A ) Superolateral view of suprasellar area showing anatomical bony land marks. (B ) Midsagittal diagrammatic illustration of the sella and suprasellar areas showing
the bony landmark, the new classification of suprasellar meningioma, and the arachnoid
layer medial lamina terminalis membrane. (C ) CT midsagittal view of sella and suprasellar area showing the anatomical bony land
mark. (D ) A superior view of cadaveric dissection at suprasellar area identifying the arachnoid
layer medial lamina terminalis membrane and its attachments with optic nerves and
chiasm. CS: chiasmatic sulcus; Lt: left; MLTM: medial lamina terminalis membrane;
ON: optic nerve; PS: planum sphenoidale; Rt: right; TS: tuberculum sella.
Fig. 2 (A ) Magnetic resonance imaging (MRI) T1 with contrast, sagittal view, demonstrates the
displacement and separation of optic chiasm posteriorly (yellow arrow ) and A1/A2 complex superiorly (red arrow ). (B ) MRI T1 with contrast images: coronal view demonstrates the displacement of both
optic nerves lateral (yellow arrows ). (C ) CT sagittal view bone window showing the measurement method for sulcal length. (D ) MRI T1 with contrast, coronal view and (E ) MRI T1 with contrast, axial view, both demonstrating the extension of the tumor
through optic canal (blue arrows ) medial to the optic nerves (yellow arrows ).
Magnetic resonance images were used to evaluate the mode of neurovascular structural
displacement, and T2-weighted images were used to evaluate the visual apparatus displacement.
Optic chiasm displacement was assessed as posteriorly displaced, superiorly displaced,
or separated from the A1/A2 complex with posterior displacement ([Fig. 2A ]). Optic nerve locations were assessed as well ([Fig. 2B ]). The A1/A2 complex location was assessed on T1-weighted contrast images and evaluated
in relation to the tumor superiorly or posteriorly. Moreover, the separation between
the optic chiasm and the A1/A2 complex was evaluated, and the distance from the A1/A2
complex to the most anterior edge of the chiasm was measured ([Fig. 2A ]). T1-weighted contrast images in the coronal plane were used to evaluate the extent
of the tumor through the optic nerve canal in relation to the optic nerve ([Fig. 2D, E ]).
The location of the chiasm and tumor extension through the canal was confirmed intraoperatively.
The presence of an arachnoid layer between the neurovascular structures and tumor
was also observed.
Results
We identified 40 cases of midline suprasellar meningiomas, 1 diaphragma sellae meningioma
(type A), 10 tuberculum sellae meningiomas (type B), 9 chiasmatic sulcus meningiomas
(type C), and 10 planum sphenoidale meningiomas (type D). Five patients with small
para-midline tumors were excluded from the analysis. Five patients had olfactory groove
meningioma ([Table 1 ]).
Table 1
Number of cases for each type
Type
A
B
C
D
Number[a ]
1
10
9
10
a Five cases were para-midline suprasellar meningioma; five cases were olfactory groove
meningioma.
Suprasellar meningiomas mainly affect middle-aged females, with an average age at
presentation of ∼44 years (median: 45; range: 25–63). The main presenting symptoms
were visual disturbances and headache ([Table 2 ]). Bilateral symmetrical visual affection was common among planum sphenoidale meningiomas
(40%), whereas asymmetric visual deterioration and unilateral visual affection were
more common in tuberculum sellae meningiomas (50 and 30%, respectively) and chiasmatic
sulcus meningiomas (44 and 55%, respectively). We had only one case of diaphragma
sellae meningioma, which showed bilateral symmetrical visual affection. The duration
of symptoms was the shortest in diaphragma sellae meningiomas, followed by chiasmatic
sulcus, tuberculum sellae, and, lastly, planum sphenoidale (5, 9, 14, and 29 months,
respectively) ([Table 3 ]).
Table 2
Demographic data
Age, y
Median: 45
Range: 25–63
Sex
F: 24, M: 3
F:M ratio: 8:1
Presenting symptoms
Visual complains: 70%
Headache: 50%
Hormonal disturbances: 30%
Table 3
Visual symptoms and duration and optic canalicular extension
Types
Visual complaints
Duration of symptoms (mo)
Canal extension
A: Diaphragma sella meningioma
Asymmetrical: (100%)
5
Inferior
B: Tuberculum sella meningiomas
Bilateral symmetrical: (10%)
Unilateral: (40%)
Asymmetrical: (50%)
Not affected: (0.0%)
12
Medial
C: Chiasmatic sulcus meningiomas
Bilateral symmetrical: (0.0%)
Unilateral: (33%)
Asymmetrical: (66%)
Not affected: (0.0%)
10
Medial
D: Planum sphenoidale meningiomas
Bilateral symmetrical: (40%)
Unilateral: (20%)
Asymmetrical: (20%)
Not affected: (20%)
29
Superomedial
In all types, the neurovascular structure was displaced together in the same direction:
superiorly in diaphragma sellae meningiomas, posteriorly and superiorly in tuberculum
sellae meningiomas, and posteriorly and inferiorly in planum sphenoidale. However,
in chiasmatic sulcus meningiomas, the neurovascular structure was separated from each
other and displaced in a different direction, leaving the optic chiasm posterior to
the tumor and the A1/A2 complex superior to it. Moreover, the sulcal length was preserved
within its normal limit in all types, except for chiasmatic sulcus meningiomas, where
it was enlarged in all cases with an average length of 8.5 mm ([Table 4 ]).
Table 4
Behavior toward surrounding structures
Types
Sulcal length (average)
Optic chiasm displacement
A1/A2 complex displacement
Neurovascular distance (median)
A: Diaphragma sella meningioma
5.9 mm
Superior
Superior
2 mm
B: Tuberculum sella meningiomas
5.2 mm
Posterior and superior
Posterior and superior
2.7 mm
C: Chiasmatic sulcus meningiomas
8.5 mm
Posterior
Superior
8.9 mm
D: Planum sphenoidale meningiomas
6.125 mm
Inferior
Inferior
1.9 mm
Discussion
The suprasellar area harbors different anatomical bony landmarks. Anterior midline
suprasellar meningiomas were previously classified into three types. Type A: true
tuberculum sellae meningiomas, which displace neurovascular structures together posteriorly;
type B: tuberculum-diaphragm sellae meningiomas, which displace neurovascular structures
superiorly and posteriorly; and type C: true diaphragma sellae meningiomas, which
displace neurovascular structures superiorly. These classifications were based on
the patency of the anterior intercavernous sinus, bone expansion, and involvement
of the diaphragma sellae.[4 ] Recently, another attempt to differentiate between planum sphenoidale, and tuberculum
sellae meningioma was published based on the tumor distribution and extension anterior
to the tuberculum sellae; this study concluded the distinction between planum sphenoidale
and tuberculum sella meningioma is less useful in terms of outcomes.[5 ]
In our study, we propose a new classification system that divides these meningiomas
into four types: diaphragm sellae (type A), tuberculum sellae (type B), chiasmatic
sulcus (type C), and planum sphenoidale meningiomas (type D) ([Fig. 1B ]). The chiasmatic sulcus houses the optic chiasm and has direct communication with
both optic canals laterally. Meningiomas in these locations exhibit different behaviors
in the surrounding neurovascular structure and underlying bone. They usually present
with visual deterioration followed by headaches as the main complaint.
In our series, we had one case of a diaphragma sellae meningioma (type A), which displaced
the neurovascular structure superiorly together. This patient presented with asymmetric
visual deterioration, with poor vision on the side where the tumor extended to the
optic canal. This meningioma preserved the sulcal length within the normal range (<7.45 mm)
([Fig. 3A–D ]).[6 ]
Fig. 3 Diagram and radiological illustration of suprasellar meningiomas subtypes: Type A
diaphragma sellae meningioma: (A ) diagram illustration of type A diaphragma sellae meningioma, (B ) CT scan sagittal view showing the sulcal length, (C ) MRI with contrast coronal view showing tumor extension in the optic canal inferior
to the optic nerve (blue arrow ), (D ) MRI with contrast sagittal view showing the displacement of the neurovascular structure
superiorly, optic chiasm (yellow arrow ) and A1/A2 complex (red arrow ). Type B tuberculum sellae meningioma: (E ) diagram illustration of type B tuberculum sellae meningioma, (F ) CT scan sagittal view showing the sulcal length, (G ) MRI with contrast coronal view showing tumor extension in the optic canal medial
to the optic nerve (blue arrow ), (H ) MRI with contrast sagittal view showing the displacement of the neurovascular structure
posteriorly and superiorly, optic chiasm (yellow arrow ) and A1/A2 complex (red arrow ). Type C chiasmatic sulcus meningioma: (I ) diagram illustration of type C chiasmatic sulcus meningioma, (J ) CT scan sagittal view showing the sulcal length, (K ) MRI with contrast coronal view showing tumor extension in the optic canal medial
to the optic nerve (blue arrow ), (L ) MRI with contrast sagittal view showing the displacement and separation of the neurovascular
structure posteriorly, optic chiasm (yellow arrow ), and superiorly A1/A2 complex (red arrow ). Type D planum sphenoidale meningioma: (M ) diagram illustration of type D planum sphenoidale meningioma, (N ) CT scan sagittal view showing the sulcal length, (O ) MRI with contrast coronal view showing tumor extension in the optic canal superior
and medial to the optic nerve (blue arrow ), (P ) MRI with contrast sagittal view showing the displacement of the neurovascular structure
posteriorly, optic chiasm (yellow arrow ) and A1/A2 complex (red arrow ).
Tuberculum sellae meningiomas (type B) were the most common type of meningioma in
this study (10 cases). In all cases that fit this category, the neurovascular structure
was displaced together superiorly and posteriorly to the tumor; the sulcal length
was preserved below 7.45 mm, and predominantly presented with asymmetric visual deterioration
or unilateral visual deterioration ([Fig. 3E–H ]).
Chiasmatic sulcus meningiomas (type C) showed unique behaviors toward the surrounding
structure; it displaced the neurovascular structure and separated the optic chiasm
posteriorly and the A1/A2 complex superiorly to the tumor with a median distance of
∼8.9 mm ([Fig. 4C ]). This observation can be attributed to the presence of an arachnoid layer that
protects the optic chiasm and optic nerves but does not cover the A1/A2 complexes;
this was observed intraoperatively ([Fig. 3I–L ]).
Fig. 4 Case demonstration of type C chiasmatic sulcus meningioma. (A ) CT scan sagittal view of the sellar area showing the sulcal length. (B ) MRI with contrast coronal view showing tumor extension to the left optic canal (blue arrow ). (C) Sagittal MRI with contrast showing the displacement and the separation of neurovascular
structure posteriorly, optic chiasm (yellow arrow ) and superiorly A1/A2 complex (red arrow ). (D ) Intraoperative picture of the arachnoid layer (medial lamina terminalis membrane)
after removing the tumor as it was resting over it and protecting the optic chiasm.
(E ) Intraoperative picture after removing the tumor showing the separation between the
optic chiasm and A1/A2 complex.
Kurucz et al performed an anatomic study that supports this observation. They named
this layer the medial lamina terminalis membrane (MLTM).[7 ] This layer was indirectly illustrated by Yasargil, as he described the chiasmatic
cistern as a space.[8 ] The superior boundary of the chiasmatic cistern matches the description made by
Kurucz et al for MLTM. We dissected two fresh cadaveric heads to examine this layer
([Fig. 1D ]). This layer is a midline arachnoid layer that extends from the posterior edge of
both gyri recti, covering both optic nerves and chiasm without protecting the A1/A2
complex, and it is attached anteriorly to the tuberculum sellae. The A1/A2 complex
is covered with a different layer, as Yasargil mentioned in his study on anterior
cerebral arteries that define the lamina terminalis cistern; its anteroinferior limit
is the superior surface of the optic chiasm.[7 ]
[8 ]
During endoscopic resection of suprasellar meningiomas, the MLTM acted as a protective
layer for the optic chiasm, and its location varies and can be predicted once the
type of meningioma is identified. This layer covered meningiomas that arose from underneath
its level, as seen in diaphragma sella and tuberculum sella meningiomas ([Fig. 3A, E ]). Moreover, we intraoperatively observed this after removing the tumor of type B
tuberculum sellae meningiomas ([Fig. 5D ]), while in types C and D, it was below the tumor and extended, protecting the chiasm
([Fig. 3I, M ]). This observation was also observed intraoperatively, as depicted in [Fig. 4D, E ] and [Fig. 6D, E ], which could be a useful intraoperative step in deciding where to start the dissection,
aiming to maintain an intact layer to protect the chiasm and minimize chiasm manipulation.
Fig. 5 Case demonstration of type B tuberculum sellae meningioma. (A ) CT scan sagittal view of the sellar area showing the sulcal length. (B ) MRI with contrast coronal view showing tumor extension to the right optic canal
(blue arrow ). (C ) Sagittal MRI with contrast showing the displacement of neurovascular structure posteriorly
and superiorly, optic chiasm (yellow arrow ) and A1/A2 complex (red arrow ). (D ) intraoperative picture of the arachnoid layer (medial lamina terminalis membrane)
after removing the tumor as it was covering the tumor and protecting the neurovascular
complex.
Fig. 6 Case demonstration of type D planum sphenoidale meningioma. (A ) CT scan sagittal view of the sellar area showing the sulcal length. (B ) MRI with contrast coronal view showing tumor extension to both optic canals (blue arrow ). (C ) Sagittal MRI with contrast showing the displacement neurovascular structure posteriorly,
optic chiasm (yellow arrow ) and A1/A2 complex (red arrow ). (D, E ) Intraoperative picture of the arachnoid layer (medial lamina terminalis membrane)
after removing the tumor as it was resting over it and protecting the optic chiasm.
In reviewing the operative notes, the A1/A2 complex was found to be protected by the
arachnoid membrane in all types, except type C (chiasmatic sulcus meningiomas).
In contrast to other types of meningiomas, the sulcal length was enlarged in all cases,
with an average length of 8.5 mm ([Fig. 5A ]).[6 ] Chiasmatic sulcus meningiomas shared the main presenting complaint with other types
of meningiomas, as visual deteriorations were the main presenting complaints, and
were mainly asymmetric visual deteriorations followed by unilateral visual affection.
In planum sphenoidale meningiomas (type D), the neurovascular structure was displaced
together, inferiorly to the tumor. The sulcal length was within normal limits. Cases
of this type commonly presented with bilaterally symmetric visual deterioration ([Fig. 3M–P ]).
Patients with suprasellar meningiomas, specifically types A, B, and C, usually present
with symptoms more rapidly than other meningioma locations and benign slow-growing
pathologies (craniopharyngioma or hypothalamic optic pathway gliomas). Despite the
relatively short period of complaints for slow-growing lesions, patients often present
with severe visual loss, in which urgent intervention is needed. They usually present
with unilateral visual deterioration with almost-normal vision or disproportionally
mild vision loss on the other side; this supports unilateral canal compression rather
than midline optic chiasm compression and displacement. Likewise, symptoms of high
intracranial pressure or hormonal imbalance are usually uncommon presentations of
these types of meningiomas. In our study, the average time spans from initial symptoms
to diagnosis were 5, 12, and 10 months, respectively. As expected, planum sphenoidale
meningiomas (type D) had a longer time from presenting symptoms to seeking medical
attention (29 months). This difference in the presentation period can be attributed
to the proximity of these locations to the optic canal and visual apparatus.
Canal extension was closer to the affected eye. This observation explains why the
main cause of visual deterioration is canal crowding and tumor extension rather than
the mass effect of the tumor size and its displacement of the visual apparatus. This
observation can change the main aims of treating these types of suprasellar meningiomas
toward optic nerve canal decompression rather than tumor debulking and decompression
of only the optic chiasm.
Types A, B, and C showed intracanalicular extension ([Fig. 3C, G, K, O ]) that was medial to the optic nerve in types B and C ([Fig. 4B ] and [Fig. 5B ]), inferior to the optic nerve in type A ([Fig. 3C ]), and superomedial in type D ([Fig. 6B ]). Only one patient with type C did not show canal extension to any of the optic
nerve canals, whose preoperative visual assessment was normal. Moreover, one patient
with type B had no canal extension, and the preoperative visual assessment was symmetrical.
This observation can make gross total resection of the transcranial approach more
difficult to achieve, as the relation of the extension will be hidden by the optic
nerves from the superolateral transcranial approach. However, achieving a lower grade
on the Simpson grading system for meningioma resection will be more difficult and
carry a higher risk with optic nerve manipulation.[3 ]
[9 ] While in the endoscopic transnasal approach, both optic nerves can be decompressed
with a similar degree of visualization without manipulation of the whole visual apparatus,
it also faces the vascularized dura initially, which starts devascularization early
in the procedure, which will facilitate tumor resection. Finally, the dura extension
beyond the tumor mass can be resected safely to achieve a lower Simpson grade in endoscopic
transnasal approaches.[10 ]
[11 ]
[12 ]
[13 ]
[14 ]
In our series, we achieved gross total resection in 86% (4/30) of the included cases.
There was no statistical significance in degree of resection and major postoperative
complications between the four subtypes.
Our study was limited by the small sample size and retrospective nature of the study
and our proposed classification may face difficulties in classifying large tumors.
Moreover, small paramedian tumors that extend to the canal before displacing the chiasm
would be unsuitable for this classification.
