Anatomical Variations of Sphenoid Sinus in South Indian Population: All That You Need for Trans-Sphenoidal Pituitary Surgery

Abstract

Pituitary adenomas are one among the most common neurosurgical tumors with an incidence of 10–25% among intracranial neoplasms (Ezzat et al., Cancer 101:613–619, 2004). Surgical management for the same has been practiced since long, and has evolved from trans cranial approach to endoscopic trans sphenoidal method (Hammer and Radberg, Acta Radiol 56:401–422, 1961). Preoperative radiological analysis with CT &MRI is inevitable in planning endonasal trans-sphenoid surgery to avoid complications because of the high variability concerned with sphenoid anatomy. The present study intends to analyze the incidence of various anatomical variations of sphenoid sinus in a cohort of south Indian population as detected by CT& MRI and assess its impact on surgical approach. Retrospective analysis of CT&MRI images of patients who underwent Endonasal Trans-sphenoidal resection of pituitary tumors at JSS Hospital Mysuru from a period of 2009 to 2020 is done. Anatomical variations of sphenoid sinus esp. degree of pneumatization, sellar configuration, septation pattern, inter carotid distance were evaluated. Results were significant and in concordance with other similar studies. Most frequently encountered pnuematization was sellar type and least was conchal type Sphenoid sinus pneumatization is directly linked to safe access to sella. Presence of septae within sinus need to be identified preoperatively to avoid damage and confusion intraoperatively. A meticulous preoperative analysis of sphenoid sinus anatomy will help surgeon in smooth conduct of a complication free surgery.

Introduction

Approaches to pituitary gland are limited because of its peculiar anatomical position. It is accessed transcranially or via sphenoid sinus. Trans sphenoidal approach is becoming the gold standard, especially for pituitary adenomas [1].

Trans-sphenoidal approach, since the first time of its attempt in1907 by Hermann Schloffer, is preferred because of the reduced mortality and morbidity.

A meticulous preoperative radiological evaluation is inevitable in planning Endoscopic Trans-sphenoidal pituitary surgery. Sphenoid sinus at birth is non pnuematised and progressively start pnuematisation by 3–5 years of age (10). It attains complete maturation by age of 10–18years [2–4], and exhibits a high degree of variation in anatomy especially in respect to pnuematisation, relation to nearby structures like; optic nerve, carotid artery, etc.

By this study we intend to analyse the incidence of various anatomical variations of sphenoid sinus in South Indian population as detected by CT & MRI imaging and evaluate its surgical implications.

Materials and Methods

This is a retrospective cross sectional study on 62 patients who underwent Endoscopic pituitary surgery at JSS Hospital, Mysuru, India between the period of 2009 to 2020.

Patients with previous history of sinus surgery and craniofacial trauma were excluded from study population.

All patients underwent extensive Preoperative evaluation including complete Clinical, Hematological, Radiological and Neurological examination, hormonal and ophthalmic evaluation including visual acuity and field of vision.

Radiological evaluation included CT: Contrast Enhanced: Axial & Coronal planes & MRI: 3Tesla scanner 3 mm Axial, coronal & sagittal images were taken.

Patients with microprolactinoma and Cushing Disease underwent Dynamic MRI for visualization of tumor. We confined ourselves to analysis of Preoperative CT &MRI of these patients for anatomical variations especially; degree of pneumatization, sellar configurations, inter-sphenoidal septation, inter carotid distance and carotid and optic dehiscence, and their intra operative implications from surgical notes and intraoperative surgical videos.

Results

The study population consisted of 20 males and 42 females with age ranging between 19 and 72 years and of south Indian origin. Sexual dismorphism, i;e difference in volume and shape of sinus in males and females were not significant in our study.

Degree of pneumatization of sinus was evaluated by both CT &MRI images esp. sagittal view. Of our 62 patients; 36patients (58%) had sellar type followed by 14(22.6%) post sellar and 12 (19.4%) presellar type. Conchal pneumatization was absent in our study population.

Sellar bulge was found to be prominent in 48(77.4%) patients while less prominent or in-appreciable in 14(22.6%). Intersphenoidal septum evaluation was easier on axial and coronal plane cuts. Complete absence of septum was noted in 9 (14.5%) cases whereas multiple intersphenoidal septum noted in 12 (19.4%) cases. Lateral deviation of septum with insertion to structures like carotid bulge (Fig. 1) and optic bulge was also noted in 3 and 2 cases respectively.

Fig. 1.

septum within sphenoid with attachment to carotid

Intercarotid distance was measured in mid-sellar coronal MRI and was found to be between 12 and 29 mm with a mean of 23 mm.

Surgical Implications

On comparing the preoperative radiological findings with available intraoperative findings: degree of pneumatization was found to be important. Conchal pnuematisation cases were not considered for trans sphenoidal surgery,while as few cases with presellar pneumatization required initial drilling (powered microdrill) (Fig. 2) to lower floor of sphenoid sinus for better visualization of sella followed by removal of floor of sella with punch because of thick wall. Out of the 14 cases with less prominent sellar bulge 6 cases required intraoperative assistance with C-arm to identify sella. In cases with intersphenoidal septum attaching to carotid bulge or optic bulge, extra care was taken by surgeon intraoperatively while removing septum.

Fig. 2.

powered microdrill (←) used to lower floor of sphenoid sinus ✩: sella bulge

Discussion

Trans-sphenoid approach has by far become the gold standard for pituitary adenoma excision [1]. The advantage lies not just in providing a less traumatic route, but most importantly lesser morbidity & mortality by avoiding retraction of brain tissue.

There are various studies assessing the considerable amount of variation in degree of pneumatization of sphenoid sinus [3–5].

Sphenoid sinus can be divided into fourgroups according to Hammer and Radberg [2, 6, 7];

Conchal or Non pneumatised: Incidence of non pnuematised is very low and was not found in our study population. It considered less favoureable for Trans-sphenoidal approach due to the long procedure time involved and its risks. With advanced technology like Navigation very few selected cases like small intra sellar pituitary adenoma with conchal type of pneumatization may be considered for trans-sphenoidal approach.

Presellar type: when pneumatization of sphenoid sinus ends anterior to anterior edge of sella turcica (Fig. 3).

Fig. 3.

Presellar type of pnuematisation

Sellar type: here posterior wall of sinus lies between anterior and posterior wall of sella (Fig. 4). It is most commonly encountered type in various populations (Table1).

Fig. 4.

Post sellar type of pnuematisation

Table 1.

Comparison of sphenoid sinus types in various populations and ethnicity

Study	Population	Technique	Conchal	Presellar	Sellar	Post sellar
Present study	South Indian	CT/MRI	–	19.4	58	22.6
Banna et al. [14]	USA	Cadaver	2.8	11.4	85.7	–
Dal Secchi et al. [15]	Brazilian	CT	–	2.0	98.0	–
Gibelli D et al. [11]	Italian	CT	–	10.0	74.0	16.0
Hiremath [16]	Indian	CT	–	1.2	98.8	–
Lu et al. [17]	Chinese	CT	6.0	28.5	65.5	–
Hamid et al. [18]	Egyptian	CT/MRI	2.0	21.0	54.7	22.3

Post sellar type: it is highly pneumatised variant with posterior wall of sinus beyond the posterior wall of sella. It is associated with distortion of anatomical landmarks and places the lateral wall structures like carotid and optic at more risk to trauma [4] due to thinning of wall. Sellar bulge is also noted to be less prominent in such cases (Fig. 4).

Sellar bulge on sphenoid roof; prominence of sella turcica is the most important surgical landmark for pituitary surgery [8]. When there is difficulty in identifying sellar bulge, it is important to identify the midline, which is done by following nasal septal floor or base of sphenoid.

CSF leak as a result of injury to posterior wall of sphenoid is common in highly pneumatised sphenoid sinus. Same was encountered in 2 of our patients and the defect was repaired by fat, fascia lata & fibrin glue intraoperatively.

In this study the most common type of pneumatization encountered was seller type which is in agreement to many of the studies conducted previously like those by Hammer et al. [2]. Few studies like those by Batra et al. [9] has shown post sellar type of pnuematisation to be the commonest type of pneumatisation in their study. Sellar type being the most common was followed by the post sellar type (22.6%) 14, and presellar type (19.4%) 12. In almost 48% patients, sellar bulge was seen prominent.

Four symmetric nuclei: (2 presphenoid & 2 post sphenoid) fuse to form body of sphenoid [2] and these zones of fusion may persist in adult life as sphenoid septum. Septation pattern and its attachment to surrounding structures is highly variable and of great surgical implication. In 36(58%) patients, single Septum was noted whereas in (27.4%) 17 cases multiple septae were noted. Complete absence of Septum was noted in 9(14.5%) cases. Study by Ossama et al. revealed an incidence of single septum to be 71.6% and multiple septae noted only in 8.7%.(7) while study by Ramakrishnan et al. observed incidence of single septum in 85.8% cases and multiple septum in 14.2% cases [10]. Lateral deviation of septum and attachment to important structures of lateral wall like Carotid (Fig. 5) and optic prominence were also noted. This was important surgically as surgeon takes extra care and precaution in such cases intraoperatively to avoid injury to these structures while removing septae.the same is discussed in a study by Gibelli D assessing risky anatomical variants for endoscopic surgery [11]. Any injury to these structures could be fatal.

Fig. 5.

Sellar type of pneumatisation

Inter-Carotid distance was found to be between 12 and 29 mm with a mean value of 25 mm, which was higher than many studies of literature [12]. Bony dehiscence of carotid wall is noted in 4–22.8% in literature [9], which also preoperatively if not identified may cause catastrophic results during procedure. However in this study pre-operatively we did not find any cases of carotid or optic nerve dehiscence which was consistent with intraoperative findings in all cases.

Limitation of Study

We in this study have selected patients who underwent trans-sphenoidal pituitary surgery, and therefore we have excluded cases of conchal pnuematisation. Conchal pnuematisation is considered to be a relative contraindication for endoscopic endonasal trans-sphenoidal resection [13].

Also the study period is short and incidence of pituitary adenoma is also less, because of which sample size is also comparatively smaller.

Conclusion

The huge variability of sphenoid sinus morphology and its relation to vulnerable structures can result in inadvertent complications during trans-sphenoidal surgery, therefore a meticulous pre-operative radiological evaluation of patient is essential for a problem free, rapid and uncomplicated surgery.

Funding

No funding was received for conducting this study.

Declarations

Conflict of interest

The authors have no conflicts of interest to declare that are relevant to the content of this article.

Ethics Approval

All procedures performed in this study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Consent to Participate

Informed consent was obtained from all individual participants included in the study.

Consent for Publication

Patients signed informed consent regarding publishing their data and photographs.