Abstract
Aim: To investigate the minimally invasive ablation of giant osteoma of the ethmoid sinuses endonasally with the assistance of an image-guidance system. Patients and Methods: A retrospective analysis was carried out on 12 patients with osteomas of ethmoid sinuses treated by endoscopic surgery with the help of a navigation system from April 2005 to October 2013. Results: Osteomas in all 12 patients were giant and connected extensively with the anterior skull base, lamina papyracea, or orbital apex, and were removed successfully with the help of an endoscope and image navigation system under general anaesthesia. In two cases (one through superciliary arch incision and the other one through labiogingival incision), the procedure was combined with an external procedure to remove osteomas. All patients were followed-up for 8 to 64 months. No recurrences were found. All symptoms gradually vanished or reduced dramatically after surgery. One case of frontal mucocele was observed and was successfully removed 5 years after removal of the osteoma. Anosmia occurred in both patients who underwent crista galli resection, and no recovery was noted 9 and 26 months later. Cerebrospinal fluid rhinorrhea was found in one case during surgery and was repaired with mucosa of inferior nasal concha immediately, and primary healing was successful. Conclusion: Endoscopic ablation of giant osteomas of the ethmoid sinuses with the guidance of a navigation system is an accurate, secure, minimally invasive procedure. A careful study of the preoperative computed tomographic scan is necessary for the success of the operation. If the lesion extensively affects the frontal sinus and maxillary sinus, a combination of superciliary arch incision and labiogingval groove incision is a simple, easy and elegant option.
Osteomas are relatively rare, slow-growing, osteogenic tumours. They are the most frequent benign neoplasms of the paranasal sinuses, usually originating in the frontal sinus and much less in ethmoid, sphenoid and maxillary sinuses. Paranasal sinus osteomas are often asymptomatic. They are detected incidentally on 3% of sinus computed tomographic (CT) scans (1) but may present similarly to rhinosinusitis (2, 3), and occasionally cause complications depending on their anatomical location (1, 4-6). The origin of these lesions is uncertain and they have a tendency to grow slowly, with a mean growth rate of 1.6 mm/year (3).
As osteomas are usually asymptomatic, they are very often incidental radiographic findings. Most authors agree that small lesions do not need surgery, suggesting periodic imaging in order to follow the growth and allow intervention before the development of complications (1). However, the osteoma may have already grown into a large tumor, merging together extensively with the surrounding structures when some symptoms arise. When osteomas expand into the orbital vault, they displace the orbital contents and give rise to symptoms such as headaches, diplopia, exophthalmos and proptosis. We report 12 cases of giant osteoma of the ethmoid sinus, with anterior skull base and intraorbital expansion, treated by an endoscopic approach with the assistance of an imaging navigation system, or with a combination of endoscopic and external approaches.
Patients and Methods
Patients. A retrospective analysis was carried out on 12 patients diagnosed with osteoma of ethmoid sinuses who were hospitalized between April 2005 and October 2013. The group comprised of nine men and three women. The mean age of the group was 37 years, with the lowest age of 14 years and the highest of 67 years. There were seven cases on the left side, five on the right, 10 with headache, seven with nasal congestion, five with purulent nasal discharge, 10 cases with nasal facial discomfort, five with feelings of facial tightness, one with diplopia and two with facial projection.
Methods. All patients underwent sixteen-detector row CT scan and 3D reconstruction preoperatively. All underwent surgery with the help of a navigation system and nasal endoscope.
Assessment by means of coronal and axial CT scan of the paranasal sinuses revealed a range of infiltration (Figure 1). There were two cases invading the frontal sinus, one invading the maxillary sinus, 11 invading the lamina papyracea; seven involving the orbital apex, of which five invaded the optic canal; 11 involving the anterior skull base, of which two with mild and two with severe hypertrophy of crista galli.
All procedures were performed under general anaesthesia. The image navigation system used was Stealth Station, ASA-610V; produced by Medtronic navigation inc (Louisville, CO, USA).
Image-guided surgery began with obtaining a CT scan. The CT scan acquisition protocol used consisted of a helical, 1-mm-thickness axial CT scan. The scans need to be taken with a 0-degree gantry tilt and contiguous scans were undertaken without metallic fiducial land marking. This allowed registration of the imaging to the patient's anatomy in the operating room.
The imaging data set was transferred via CD-ROM to the operating room, where it was loaded into the workstation. The images were then brought up on the image navigation system prior to the procedure and checked for image quality and accuracy.
Endoscopic uncinectomy and ethmoidectomy were carried out firstly. The ethmoid osteoma was identified with the assistance of the image navigation system. The tumor was removed from inside little by little under endoscopy (Figure 2). The surgeon needed to frequently probe the location of the current operation with the image navigation system. A long-arm abrasion drill was necessary, using a diamond burr in place of the cutting burr when the procedure was close to the edge of the tumour. When the tumor had been hollowed out from inside, an eggshell-like structure was all that remained. A thin elevator was then used to remove tumor shell. The orbital fascia, optic nerve sheath and anterior cranial base dura had to be exposed in order to remove the tumour completely. There were two cases with severely enlarged crista galli which had to be removed and two cases of mild hypertrophy in which the crista galli were preserved.
Seven cases of orbital fascia, five of optic never sheath and six of frontal cranial dura were exposed during the operation. The osteoma had invaded across the middle line in two cases. The top portion of the nasal septum had to be excised in order to operate simultaneously on both sides of the nasal cavity. A combination of external eyebrow incision and endoscopic techniques were required in two cases, when the osteomas was growing forward and upward to the supraorbital rim, due to the limited access and visibility of endoscopy.
Antibiotics were applied for 5 to 7 days after the operation. It was necessary to use an antibiotic which was able to penetrate the blood–brain barrier, such as ceftriaxone, whenever the cerebral dura mater was exposed or broken. The treatment was the same as the endoscopic nasal sinus surgery, including nasal irrigation and topical steroids after the nasal stuffing was extracted.
Results
All ethmoid osteomas were successfully removed without major operative complications. Two cases (one through superciliary arch incision and one through labiogingival incision) were combined with an external procedure to remove the osteoma. The follow-up was 8-64 months, with a mean time of 22 months. No recurrences were reported. All symptoms gradually vanished or were reduced dramatically after surgery. One case of frontal mucocele was observed and was successfully removed 5 years after osteoma excision. Anosmia occurred in both patients who had undergone crista galli resection, and no recovery was observed within 9 months and 26 months; cerebrospinal fluid rhinorrhea was found in one of the two patients during surgery and immediately repaired with the mucosa of inferior nasal concha, with successful primary healing. The symptoms of headache and nasal congestion vanished gradually after the operation. One patient complained regarding the repeat nasal scab and of a peculiar smell for 6 months. The symptoms gradually vanished after the nasal irrigation was intensified.
Case Presentations
Case 1. A 52-year-old man was referred to our Department with a 3-month history of dizziness and purulent nasal discharge. Assessment by means of coronal and axial CT scan (Figure 3) of the paranasal sinuses revealed a huge osteogenic lesion arising from the left ethmoidal labyrinth, expanding laterally into the orbit and cranially up to the anterior skull base. Endoscopic surgery with the assistance of the image navigation system was carried out 3 days after the patient was admitted into hospital. The procedure was performed under general anaesthesia. The osteogenic lesion was found to have fused together with the frontal cranial base, the lamina papyracea and the optic canal during the operation. The tumor was removed from inside little by little. The orbital fascia and optic canal were exposed partially (Figures 4 and 5). All the symptoms had disappeared two weeks after the operation. A 4-year follow-up indicated no recurrence.
Case 2. A 43-year-old man came to our Department with a 6-month history of progressive headache and nasal congestion. CT scan (Figure 6) showed a giant osteogenic lesion arising from the right ethmoid sinus and expanding laterally into the orbit and cranially up to the anterior skull base, with severe crista galli hypertrophy. Endoscopic surgery with the assistance of the image navigation system was applied under general anaesthesia 4 days after the patient was admitted to the hospital. The osteogenic lesion was found to have merged together with the crista galli except the frontal cranial base, the lamina papyracea and the optic canal during the operation. The tumor was removed from inside like Insect erosion. The orbital fascia and optic canal were exposed partially. The crista galli and partial frontal cranial base were removed (Figure 7). Cerebrospinal fluid rhinorrhea was also found during the operation for this patient and immediately repaired with the mucosa of inferior nasal concha. The cerebrospinal rhinorrhea successfully healed. The symptoms of headache and nasal congestion had disappeared two weeks after the operation. A 26-months follow-up indicated no recurrence. However, the patient lost his sense of smell and this had not recovered.
Discussion
The ethmoid osteoma is a benign tumour which grows slowly. As osteomas are usually asymptomatic, there exist very often incidental radiographic findings, and most require only periodic imaging in order to follow the growth and allow intervention before the development of complications. However, the osteoma may grow into a large tumour, merging extensively with the surrounding structures. Progressive headache, dizziness and chronic mucosal inflammation are common clinical manifestations. Nasal and facial discomfort, headache and nasal congestion were the three most common symptoms in our series. Purulent nasal discharge and facial tightness are less common symptoms. Diplopia and facial projection are rare symptoms of patient complaint.
A detailed assessment of the margins of the tumour and definition of its relation with the surrounding structures is required in order to choose the most precise approach (7). A CT scan is a fundamental tool that not only permits diagnosis but also allows the correct surgical approach to be planned. Three-dimensional CT scan is even described as a tool for defining the extension of ethmoid osteomas (8). In our case, careful analysis of the CT scan in the axial and coronal views determined the size of the tumour and differentiated osteoma from soft-tissue tumors or fibrous displasia. Magnetic resonance imaging offers more exact evaluation of the margins of the lesion and finely reveals intraorbital extension but not intracranial invasion.
Surgery is the only treatment of choice for symptomatic ethmoid osteomas, however, the best approach is under discussion and depends on the tumour extension and the occurrence of complications (9). Traditional surgical approaches to the involved sinuses are through external fronto-ethmoidectomy, lateral rhinotomy or osteoplastic flap technique (1). Damage to the surrounding structures frequently occurs in the traditional surgical approaches due to poor visualization.
The recent development of endoscopic techniques and instruments has offered an alternative approach to sinonasal osteoma surgery, allowing for direct visualization of the mass and reducing the morbidity and cosmetic complications (1, 4). Technological advantages in endoscopic instrumentation have expanded the use of endoscopic surgery for the management of ethmoid osteomas. Endoscopic transnasal resection is ideal for tumors confined to the ethmoid and nasal cavity. The main advantages of the method are the minimal soft-tissue dissection, the absence of facial bony disruption, and the avoidance of a facial incision. The magnification and the differently angled view, which are possible with the use of endoscopes, may facilitate the removal of osteoma with minimal morbidity (10). When osteomas are large and have expanded into the orbit and anterior cranial base, a combination of external and endoscopic technique are required, due to the limited access and visibility of endoscopy.
However, for giant ethmoid osteomas, which usually extend out of the range of the ethmoid sinus and merge with the frontal cranial base, lamina papyracea and optic canal, it is difficult to distinguish the tumour boundary, even using a combination of techniques. The image navigation system is able to solve this problem well. With its help, the boundary of the tumour can be probed simultaneously.
The need for minimally invasive surgery of the head and neck in order for resection to be precise and safe has prompted the development of image-guidance systems to assist the surgeon with intraoperative anatomical localization. These systems use computerized tracking devices to monitor the position of endoscopic instruments relative to the patient's anatomical landmarks. The location of these instruments is depicted on a 3-dimensional video display of the preoperative CT or magnetic resonance imaging scan in axial, coronal and sagittal frames simultaneously.
Initially developed for neurosurgical procedures that required head fixation in a stereotaxic frame, image-guidance systems have recently been introduced that allow for free head movement during surgery. Due to the better resolution of CT scans in a bony anatomy, and little possibility of tissue shift intraoperatively, these systems have been used for procedures involving the paranasal sinuses, skull base, and temporal bone. Surgery in these regions is also particularly well-suited for image-guidance applications because of the proximity to the orbit and cranial cavities, which demands a high degree of anatomical precision (11).
Image-guidance based navigation can aid in directing the surgeon's attention to the nearby structures. It is increasingly utilized in skull base surgery (12-15). Its efficacy in the treatment of skull base tumors has already been shown (16). With its high application fidelity, the system presented in this study provides genuinely useful feedback to the surgeon for case-specific anatomic orientation, planning, and simulation of the surgical approach, intraoperative guidance, identification and avoidance of vital elements, and assessment of the extent of possible resection. It provides information on the interface between the tumor and normal tissue, the tumor's proximity to critical structures, and the possible location of the residual tumor.
Giant ethmoid osteomas are able to invade forward and upward from the frontal sinus. It is not difficult to remove such tumours by endoscopic surgery with the assistance of the image-navigation system in most cases. However, in some rare cases, it is necessary to combine external eyebrow incision with endoscopic surgery when the osteoma extends over the supraorbital rim. Regarding aesthetic considerations, there is no need to shave off eyebrow hair since there is no evidence indicating that it increases the risk of postoperative infection.
When the maxillary sinus or maxilla is involved, it is a good approach to combine the endoscopic surgery with a labiogingival incision. The nasal approach with endoscopy is appropriate for situations in which the medial, posterior or superior wall of the maxillary sinus is involved. However, when the lateral, frontal or inferior wall of the maxillary sinus is involved, a labiogingival incision is able to improve the visualization and enlarge the operating space without negatively influencing appearance.
Compared to the frontal cranial base and orbit, it is common for ethmoid osteoma to invade the sphenoid sinus due to the bone wall between them being very thin. The carotid canal and optic canal are on the lateral wall of the sphenoid sinus, which increases the operative risk but not operative difficulties because the ethmoid sinus and sphenoid sinus are both near the midline and suitable for the endoscopic surgery with the assistance of an image-navigation system.
This system is a good way to preserve a thin bony wall outside of the orbital fascia for the purpose of protecting the orbital contents. The thin bony wall may not be preserved when an osteoma protrudes into the orbit severely and the patients exhibit exophthalmos and diplopia; the orbital fascia has to be exposed. When the defect is less than 2 cm in diameter, it is not necessary to repair the defect. Saetti et al. reported an endoscopic method to rebuild the medial orbital wall when the defect is extensive (17). There was one patient whose defect of the medial orbital wall was approximately 3×2 cm in our series without our undertaking any rebuilding, but no complications took place after the operation.
In cases of giant ethmoid osteoma, it is not rare that the crista galli is involved. The crista galli should be removed if it is severely hypertrophic. The crista galli and cerebral dura mater usually connect tightly. Great caution should be taken to avoid breaking through the dura mater. The defect should be repaired immediately if cerebrospinal rhinorrhea is found during the operation. We had two cases with severely enlarged crista galli which had to be removed and two cases of mild hypertrophy in which the crista galli was preserved.
Conclusion
Endoscopic ablation of giant osteoma of the ethmoid sinuses with the guidance of a navigation system is an accurate, secure, minimally-invasive procedure. A careful study of the preoperative CT scan is necessary for the success of the operation. If the lesion extensively affects the frontal and maxillary sinuses, a combination of superciliary arch incision and labiogingval groove incision is a simple, easy and elegant option.
Footnotes
↵* These Authors contributed equally to this study.
- Received January 4, 2016.
- Revision received February 17, 2016.
- Accepted February 18, 2016.
- Copyright© 2016 International Institute of Anticancer Research (Dr. John G. Delinassios), All rights reserved