Technical Note of the Endonasal Endoscopic Transethmoidal Transcribriform Approach (EETTA) to the Anterior Cranial Fossa: An Update of the Surgical Technique, Indications, and Limitations

Highlights

What is the main finding?

• The endonasal endoscopic transethmoidal transcribriform approach (EETTA) is a minimally invasive alternative for treating midline anterior cranial fossa (ACF) tumors, offering advantages such as no brain retraction, early vascular control, reduced blood loss, improved visualization, faster recovery times, and a preserved cosmetic appearance compared to traditional transcranial approaches.

What are the implication of the main findings?

• EETTA can be offered as a surgical option for appropriately selected patients with small-to-moderate-sized midline tumors, potentially avoiding more invasive craniofacial approaches and their associated higher morbidity (35%) and mortality (5%) rates.
• The learning curve and specialized training are critical factors for success with EETTA, emphasizing the need for patients with these tumors to be referred to tertiary care centers with experienced multidisciplinary teams to achieve optimal outcomes and minimize complications.

Abstract

Background: In the last few decades, endoscopic endonasal approaches (EEA) have revolutionized surgical access to the sellar region and anterior cranial fossa (ACF). One technique, the endoscopic endonasal transethmoidal transcribriform approach (EETTA), offers distinct advantages over traditional open transcranial approaches, such as reduced morbidity, shorter hospital stays, faster recovery, and a reduced risk of neurological deficit due to less brain tissue manipulation. Methods: We present a comprehensive step-by-step description of the EETTA surgical technique, illustrated through four representative cases of varying pathologies treated at our institution. The anatomical boundaries—including the lamina papyracea, anterior and posterior ethmoidal arteries, and frontal sinus—and the surgical corridor are detailed alongside indications, technical nuances, limitations, and operative recommendations. Results: Four cases demonstrate the versatility of EETTA across diverse pathologies: two olfactory groove meningiomas (including one WHO grade 2 and one recurrent case with invasive skull base involvement), an esthesioneuroblastoma (ENB), and a recurrent inverted papilloma requiring combined transcranial and endoscopic resection. Near-total or gross-total resection was achieved in all cases. The indications, nuances, and limitations of this approach are discussed, along with tips for successful surgery. Conclusions: The EETTA represents an important minimally invasive option for ACF tumors extending into the nasal cavity, with midline involvement limited medially by the lamina papyracea. Success requires a thorough understanding of skull base anatomy, meticulous multilayer reconstruction techniques, and appropriate patient selection, based on the tumor location and lateral extension. While cerebrospinal fluid (CSF) leak remains the primary concern, contemporary techniques have substantially reduced this complication rate.

1. Introduction

The anterior cranial fossa (ACF) is susceptible to various neoplastic pathologies, such as meningiomas [1], adenocarcinomas [2], and olfactory groove neuroblastomas [3,4]. The extent of resection, as well as the surgical technique utilized, depends on the lesion’s location, extent, and involvement of neurovascular structures, as well as the baseline preoperative functionality of these structures [5,6]. A good example is the olfactory groove meningioma, for which open approaches, such as the transbasal bifrontal and pterional, have been the preferred techniques [7,8,9]. However, these techniques sometimes require a larger area to expose the tumor, which can lead to greater brain retraction or manipulation [8]. Furthermore, complications such as hematoma, cerebral edema, hydrocephalus [8], venous infarction, cerebrospinal fluid (CSF) leakage, and bone flap infection remain significant concerns [10], with a 30% morbidity rate and a mortality rate of up to 5% [7,11]. The endoscopic endonasal transethmoidal transcribriform approach (EETTA) is a cost-effective [5,12], less invasive alternative for achieving direct [13], early access to the tumor and its blood supply, and for attaining gross-total resection of the lesion [14], especially in those with endonasal invasion [15,16,17]. However, EETTA has several limitations, including a greater risk of CSF leakage [15,16,17], compromise of the olfactory system [1], and limited access for large and giant tumors or those with lateral extension [18]. This opens a discussion of when endoscopic endonasal approach (EEA) is a better option compared to classic open transcranial approaches, and more specifically, techniques such as EETTA. Our series of illustrative cases show where EETTA was the alternative approach for tumor resection, describing the surgical technique, outcomes, and nuances, and discussing its current uses and alternatives.

2. Materials and Methods

Following CARE Guidelines for case series, we included four representative cases of varying neoplastic pathologies operated at an advanced neurological care center in Colombia.

The descriptive clinical and operative data were retrospectively collected from medical records, including initial presentation, visual and endocrine outcomes, and perioperative complications.

This study was reviewed and approved by the board and the ethics committee, in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all patients featured in this report.

Surgical Technique

Under general anesthesia, in accordance with institutional protocols, prophylactic antibiotics are administered, and urinary and arterial line catheters are placed. A lumbar drain is placed to facilitate the closure of the skull base dura mater. The head is fixed in a Mayfield holder, rotated slightly right, and extended ~30° to optimize ACF exposure [2]. Neuronavigation is calibrated and the lateral thigh is prepared for autologous fat and fascia lata harvest.

Using a rigid endoscope, the mucosa near the sphenopalatine artery, the anterior/posterior ethmoidal arteries, and the middle turbinates are infiltrated with 1% lidocaine and epinephrine.

The anatomical limits of the EETTA include the posterior wall of the frontal sinuses (anteriorly), lamina papyracea (laterally) (Figure 1), and anterior/posterior ethmoidal arteries (posteriorly). In most cases, complete ethmoidectomy and Draft II frontal sinusotomy are performed. Given the potential compromise of olfaction, this approach is reserved for select pathologies such as ENBs, sinonasal carcinomas, and some olfactory groove meningiomas.

The first part of the procedure begins with harvesting a large vascularized nasoseptal flap, temporarily hidden in the nasopharynx. A superior septectomy enables bi-nostril access to the ventral skull base. Following identification of the uncinate process, uncinectomy is initiated at its anterior attachment, with the incision oriented parallel to the lamina papyracea, to avoid orbital damage, and extended inferiorly and laterally toward the maxillary ostium. Bulla resection and infundibulotomy are performed, revealing the ethmoidal bullae and frontal recess. Ethmoidectomy proceeds through the bulla to expose the fovea ethmoidalis, where the anterior ethmoidal artery is coagulated and divided. The mucosa and olfactory epithelium over the cribriform plate are cauterized and removed, followed by bilateral cribriform plate resection to the lamina papyracea margins. The duramater over the cribriform plate and fovea ethmoidalis is excised to expose the rectus gyri. Tumor debulking is performed via a standard micro-neurosurgical technique. Although olfactory nerves may occasionally be preserved, functional olfaction is unlikely after epithelial removal. Tumor resection is completed. Hemostasis is achieved using a FLOSEAL^® (Baxter) hemostatic matrix. Reconstruction follows a multi-layered technique with an acellular dermal allograft, autologous fascia lata graft, and a vascularized pedicled nasoseptal flap. Large cribriform plate defects and associated dead space beneath the brain may be packed with autologous fat graft; however, Gelfoam^® (Pfizer) sponge is preferred to facilitate postoperative imaging whenever possible. The nasoseptal flap is finally positioned over the surgical bed. Further hemostasis is completed. Afterward, the patient is transferred to the neurointensive care unit for monitoring, and the lumbar drain is removed on postoperative day 3.

3. Results

3.1. Case 1: Meningioma

A 72-year-old man presented with bilateral hyposmia. The patient had no remarkable medical history. Aside from the hyposmia, no other deficits were noted during his physical examination. The magnetic resonance imaging (MRI) was consistent with a meningioma of the olfactory groove, with extension into the nasal cavity through the cribiform plate (Figure 2). The decision to perform an EETTA was based on the tumor’s endonasal extension and the prior onset of olfactory compromise. Regarding specific surgical features for this case, it is important to note that the tumor borders are identified endonasally (Figure 3), and the normal dura is then incised. Afterward, a brain cuff is identified, and the tumor is dissected free from the falx cerebri. A satisfactory near-total resection (NTR) (>90%) was achieved. The en-plaque component of the planum sphenoidale was intentionally not resected, due to the increased risk of CSF leakage. The postoperative period was uneventful, and the patient was discharged on postoperative day 4. The histopathology was consistent with a WHO grade 2 meningioma [19]. Consequently, further complementary radiotherapy was performed.

3.2. Case 2: Recurrent Meningioma

A 27-year-old man presented with severe headaches 2 years after a transcranial resection of a large olfactory groove meningioma. The patient had no other significant medical history. On his physical examination, the patient was anosmic. The follow-up MRI demonstrated a large recurrence of the tumor with invasive infiltrative compromise of the anterior cranial base and extension into the nasal cavity through the lamina papyracea (Figure 4). The decision-making board decided to perform EETTA for a maximal safe resection and decompression, given the large extension into the nasal cavity. Intraoperatively, the intracranial component of the tumor compromising the planum sphenoidale demonstrated an exaggerated hyperostosis, with lateral extension into the orbital roof bilaterally. This component was intentionally left. The postoperative MRI showed a significant decompression, with a satisfactory resection of the most anterior and inferior aspect of the recurrence. The postoperative period was uneventful, and the patient underwent complementary radiotherapy for the thin remnant.

Intraoperative imaging of endonasal resection of an olfactory groove meningioma. (a) The right anterior ethmoidal artery is pointed at with an arrow before coagulation. (b) Endonasal view of the endonasal component of the tumor. The normal dura mater is exposed bilaterally from below (arrowheads). (c) A brain cuff is shown (arrowheads), and the tumor dissection is demonstrated. (d) An inlay positioning of a dura patch is observed (arrows denoting the inlay placement).

3.3. Case 3: Inverted Papilloma

A 65-year-old man presented with progressive bilateral proptosis, right amaurosis, and anosmia. He had undergone resection of an infiltrative endonasal tumor at a different institution, which was consistent with an inverted papilloma. The patient was referred for complementary radiotherapy but was unable to complete it due to multiple access restrictions imposed by his health insurance company. A follow-up MRI showed a giant tumor compromising the endonasal cavity and the ACF (Figure 5). The patient presented to the emergency department, and it was decided to offer an emergent rescue resection for maximal safe decompression and further complementary radiation. A combined one-stage transcranial trans-basal approach and EETTA was performed, given the lateral intracranial extension, which limited access from below. A satisfactory NTR was performed. Intraoperatively, no clean margins were achieved due to bilateral infiltration into the lamina papyracea, despite successful decompression both endoscopically and intracranially (Figure 6), with improvement in his symptoms.

3.4. Case 4: Esthesioneuroblastoma

A 70-year-old woman presented with left visual loss and exophthalmos. An endonasal biopsy was done in another institution, which was consistent with an ENB. The patient was offered an endonasal resection with palliative intention, given the advanced large invasion into the cranial base (Figure 7). An EETTA was performed, allowing maximal safe resection and decompression of the left orbit and the endonasal cavity. The intracranial component was also resected, and closure was achieved with a large multilayer reconstruction. In this case, a multilayered reconstruction was performed; however, given the compromised nasal mucosa, a nasoseptal flap could not be harvested. The patient presented with a CSF leakage on her postoperative day 28, requiring a reintervention. Interestingly, the leakage was found at a different location, the middle clivus, which was also covered with fascia lata and fat graft. No further complications were noted (

Table 1. Key patient outcomes of 4 cases.

Case	Diagnosis	Age/Sex	Surgical Approach	Extent of Resection	Postoperative Course	Adjuvant Therapy	Key Outcome
1	Meningioma (olfactory groove, WHO grade 2 [19])	72/M	EETTA	NTR (>90%); en-plaque planum sphenoidale left intact	Uneventful; discharged POD 4	Radiotherapy	Good surgical outcome with disease control via adjuvant RT
2	Recurrent meningioma	27/M	EETTA	NTR; hyperostotic planum/orbital roof component left	Uneventful	Radiotherapy	Effective decompression with stable residual disease
3	Inverted papilloma (recurrent, invasive)	65/M	Combined transcranial transbasal + EETTA	NTR; no clean margins	Symptomatic improvement postoperatively	Planned radiotherapy	Successful decompression despite residual infiltrative disease
4	Esthesioneuroblastoma	70/F	EETTA	NTR (endonasal + intracranial)	CSF leak on POD 28 → reoperation; resolved	Palliative intent	Adequate decompression; delayed CSF leak successfully managed

Note: WHO = World Health Organization, M = male, F = female, EETTA = endoscopic endonasal transethmoidal transcribriform approach, NTR = near-total resection, CSF = cerebrospinal fluid, POD = postoperative day, and RT = radiotherapy.

).

4. Discussion

The EETTA is an efficient and minimally invasive alternative for treating tumors in the midline of the ACF, especially those with extension into the nasal cavity [20]. We demonstrate the versatility of this approach in managing a variety of pathologies. The trans-ethmoidal corridor lies lateral to the middle turbinate and provides access to the fovea ethmoidalis, the orbital apex, and the lateral sphenoidal sinus. The trans-ethmoid approach is also helpful in exposing the maxillary sinus if needed [21]. The anatomic limits of the EETTA are the posterior wall of the frontal sinuses anteriorly, the medial orbits (lamina papyracea) laterally, and the most remarkable landmarks: the anterior and posterior ethmoidal arteries, posteriorly [11].

4.1. Indications and Advantages

EETTA is a suitable approach for small tumors [20,22] (less than 30–40 mm) [1,2] that are medial to the optic nerves [2,18] with or without minimal lateral extension beyond the supraclinoid internal carotid arteries. It is also suitable for patients with recurrent meningiomas at the cribriform plate extending into the paranasal sinuses [7], as was the case in one of our illustrative cases. Usually, the EETTA is indicated for benign tumors in the ACF, such as meningiomas, osteomas, and papillomas [11]. This approach is used to repair encephaloceles of the cribriform plate and fovea ethmoidalis [11]. The EETTA may be a good strategy if the basal dural attachment is between the medial walls of the orbit [7].

In addition, the indications for ENB resection include tumor burden that can be removed without injury to neurovascular structures, an enlarging tumor, and a tumor requiring a diagnosis. Furthermore, current data indicate that EETTA and stereotactic radiosurgery/fractionated radiotherapy may be as effective as the craniofacial approach for this type of tumor [11].

The advantages of this approach include the absence of brain retraction; straightforward access to the lesion and to the involved bone and dura, with an early management of the vascular supply (ethmoidal arteries) [11,23]; decreasing blood loss [24]; and improved visualization of the cranial midline and tumor margins [2,10,15,16,18,25,26]. Furthermore, it avoids scarring while preserving the cosmetic appearance [11,15,18,23], and has been shown to reduce surgical times and length of hospital stays [12,13,26] in specific scenarios [3]. Similarly, EETTA has been shown to reduce postoperative brain injury related to retraction during transcranial approaches, leading to faster edema resolution and reduced postoperative encephalomalacia [25].

4.2. Limitations and Disadvantages of the EETTA

Like other approaches, EETTA has multiple limitations and specific indications determined primarily by bone, vascular, and orbital structures. The EEA for resection of tumors infiltrating the sinus dural margin and optic apparatus is challenging and may only be offered at tertiary care centers. In addition, EEAs are limited in treating tumors that are too lateralized in the sphenoid wing or beyond the mid-pupillary line, as well as tumors located high along the posterior table of the frontal sinus. Combining endoscopic techniques with traditional open techniques can help us to overcome some of these limitations [27]. The National Comprehensive Cancer Network Clinical Practice Guidelines in Oncology for head and neck cancers recommend systemic therapy as part of the overall treatment plan for some sinonasal malignancies, but are otherwise unclear about treatment selection. Radiotherapy treatment may reduce the risk of tumor recurrence, improve survival [24], and potentially avoid the need for enucleation; however, radiation treatment can result in significant patient morbidity, and data guiding radiotherapy management are limited. Given these considerations, patients presenting with these unique tumors may require enrollment in clinical trials and/or referral to major medical centers specializing in this disease [18]. Specialized instrumentation and anatomical knowledge may also be necessary for these approaches, which a multidisciplinary trained team can better tackle. Reconstruction to prevent CSF leak is critical and requires a team approach with experience in all components of the reconstructive ladder. An en bloc resection could aid in the dissemination of cancer cells and ensure cleaner margins; however, the limited nasal corridor, which hinders visualization of critical neurovascular structures (e.g., the frontal lobe and anterior cerebral arteries), makes this approach challenging. There has not yet been a study suggesting that en bloc resection reduces recurrence rates compared with piecemeal resection for ENB.

One of the limitations of the EETTA is the access to lesions with extensive lateral involvement through the ACF or above the orbital roof behind the orbital midline, which extend laterally towards the frontal sinus [15], which is not technically possible to resect [28]. Therefore, extensive lesions or a carcinoma that requires negative margins [4] cannot be completely resected by EETTA, since tumor residues could remain and recurrence could occur [7]. In select cases, a piecemeal gross-total resection with negative margins can be obtained, followed by fractionated radiotherapy or radiosurgery [15].

The current standard of care to achieve bloc resection with negative margins, in some cases, involves a craniofacial approach [11]. However, this technique is associated with some risks (5% mortality and 35% morbidity) [11]. There is no data that clearly shows that piecemeal removal with a negative margin is less effective than en bloc resection [11]. Similarly, only 70% of patients undergoing extensive craniofacial surgery achieve negative margins, suggesting that they may be a subgroup for whom negative margins are unattainable, regardless of the procedure’s aggressiveness [7]. Complete removal of large tumors that extend up behind the frontal sinus or attach beyond the lamina papyracea is challenging [11]. The “cortical cuff” reduces the chance of a vascular injury by shielding the anterior cerebral vessels from the non-eloquent brain tissue; [4] it separates the tumor and vasculature [7,25]. The lack of a “cortical cuff” may affect the extent of resection or increase the risk of neurovascular injury [1].

Another disadvantage of the EETTA is that, due to extensive manipulation of the skull base, multiple defects may occur, leading to CSF leakage [1,2,29]. CSF leaks may prolong hospitalization and carry a risk of meningitis or a central nervous system infection [15], which are arguments often used against EEA. Nevertheless, no intracranial infections were observed in our series, supporting the validity and safety of this approach. Postoperative sinusitis is common, but typically manageable with nasal irrigation, antibiotics, and close rhinologic follow-up. Management depends on leak location, severity (flow volume) [29], and etiology [30]. Very anterior leaks just behind the frontal recess or in the back wall of the frontal sinus are difficult to address endonasally and may require craniotomy [11]. However, when there is a small-volume leak and a meticulous multilayer closure has been performed, it can often be managed initially with lumbar drainage before considering surgical reintervention [26]. Therefore, repairing or reconstructing these defects can be a significant challenge during closure [1,17].

4.3. Complications

CSF leak risk is the most significant EEA complication [31]. While early series reported leak rates of 20–30% [21,32], contemporary experience has reduced this to approximately 4–10% [1,33,34] or lower [31] with increasing surgical expertise [1]. In a study of 10 patients who underwent multilayered repair, the CSF leakage rate was 0%, and the authors also observed that over the previous 8 years, only one leak occurred in 44 patients [1].

At our institution, the management of pituitary adenomas with sellar and suprasellar extension, many of which required advanced reconstructive strategies, including nasoseptal flap harvesting, fascia lata and fat grafting [13,29], dural patch placement, and lumbar drainage, has been a cornerstone of training, with around 40 cases up to this time. Based on these cases, we established a standardized protocol for postoperative cerebrospinal fluid leakage: (1) continuation of lumbar drainage, and (2) if leakage persists, prompt revision surgery to identify the source and implement either a new vascularized flap or repeat multilayer reconstruction. This also supports the main idea that appropriate training and a surgical educational curve are needed for better outcomes.

One of the EEA complications is postsurgical anosmia [7,8], secondary to the manipulation and resection of the olfactory epithelium/fibers, with damage to the olfactory pathway [1,10].

According to Roa et al. [22] in EEA studies, 27% of the patients were already anosmic when taken to surgery. In our cases, all patients were anosmic before surgery, and this was one of the criteria used to perform EETTA. Patients with anosmia or hyposmia are candidates for EETTA; however, if their sense of smell is intact, a transcranial approach should be recommended.

In patients with a tumor located on only one side of the nasal cavity, a unilateral approach can be performed, thereby avoiding postoperative anosmia [1,35]. Different techniques, such as the endoscopic L-shape approach [8], the non-placement of a nasoseptal flap [36,37], or nasal turbinate preservation [38], are strategies that have been described in various studies, but the literature remains limited. We emphasize that, in all cases, the patients remained anosmic.

It is important to acknowledge that this study is limited to four cases, which constrains the generalizability of the findings. Nevertheless, the objective was not broad extrapolation but rather to refine and illustrate this surgical approach through carefully selected cases representing the most challenging and illustrative scenarios. These cases highlight the approach’s potential utility in complex ACF pathologies characterized by significant endonasal compromise (

Table 2. Comparative analysis of endoscopic endonasal trans-ethmoidal trans-cribriform approach (EETTA) versus traditional transcranial approaches for anterior cranial fossa tumors.

Parameter	EETTA	Transbasal	Pterional	Supraorbital/Mini-Pterional
Surgical corridor	Endonasal transethmoidal transcribriform	Bifrontal craniotomy	Frontotemporal craniotomy	Eyebrow/supraorbital craniotomy
Optimal tumor location	Midline ACF	Midline and lateral ACF	Lateral ACF	Small lateral ACF
Brain retraction	None	Significant	Moderate	Minimal
Early vascular control	Yes	No	Variable	Partial
Tumor visualization	Excellent midline	Wide bilateral	Excellent lateral	Adequate (small tumors)
Olfactory preservation	No	Possible	Usually preserved	Usually preserved
CSF leak risk	Moderate	Moderate	Low–moderate	Low
Cosmetic impact	None	Bicoronal scar	Temporal hollowing	Minimal
Main advantages	No retraction, direct midline access	Wide exposure, oncologic margins	Versatile lateral access	Minimally invasive
Main limitations	Limited lateral reach	Higher morbidity	Brain retraction	Restricted exposure

Note: EETTA = endoscopic endonasal transethmoidal transcribriform approach, ACF = anterior cranial fossa and CSF = cerebrospinal fluid.

).

5. Conclusions

We provide a detailed step-by-step analysis of the EETTA surgical technique, clarifying its anatomical features, surgical boundaries, and technical limitations. Our case series—spanning invasive recurrent meningiomas and sinonasal malignancies—demonstrates the approach’s capacity to address complex pathologies with improved safety profiles. Despite an initial decline in popularity for the EETTA due to concerns about elevated CSF leak rates, we advocate for a thoughtful reassessment of this technique in select scenarios. Some of these options include olfactory groove meningiomas with endonasal invasion, where direct corridor access remains the most anatomically sound strategy.

The technique serves as an essential complementary option for midline ACF lesions, with endonasal extension limited by the lamina papyracea. With advancing endoscopic technology and growing surgical experience, EETTA will continue to evolve and potentially broaden its applications while upholding its core principle: achieving maximal safe resection through the least invasive approach possible—the defining principle of modern neurosurgical innovation.