Analysis of the Lamina Papyracea Dehiscence Based on Computed Tomography Findings

Objectives:

Aim to evaluate the incidence and characteristics of nontraumatic dehiscence of the lamina papyracea (LP) via computed tomography (CT).

Methods:

The authors retrospectively studied 893 patients' history and paranasal sinus CT from February to September 2020. The datum of incidence and the characteristics of LP dehiscence were collected and analyzed.

Results:

The LP dehiscence was identified in 23 of 893 patients (2.58%). Lamina papyracea anatomical variations were categorized into Grade I, II, and III, which account 69.56%, 21.74%, and 8.70% of the entire dehiscence group. The average depth of LP ingression was 5.5 ± 0.7 mm. There was no statistical difference between bilateral incidence. The medial rectus muscle was involved in 3 lesions. In all CT reports, this anatomic variation was misdiagnosed as ethmoid sinusitis in 8 cases.

Conclusions:

Preoperative cognition of the anatomic variation of LP via CT is conducive to decrease misdiagnosis and postoperative complications.

The lamina papyracea (LP) is a high-risk area for endoscopic sinus surgery. The LP is also the weakest area of the medial orbital wall, and congenital, traumatic, iatrogenic and inflammatory factors can lead to the LP dehiscence. The incidence of this variation has been reported from 0.76% to 10.0%. ^1,2 Anatomical variation of the LP with the orbital content herniated into the ethmoid sinus was considered as a possible cause of orbital complication in endoscopic sinus surgery. In this study, we focused on the incidence and features of nontraumatic LP dehiscence by reviewing and analyzing a large number of sinus computed tomography (CT). In particular, we evaluated the depth, range and location of LP ingression. This article has reinforced that CT plays a vital role in avoiding surgical complications and can detect anatomic variation before operation. As a result, preoperative evaluation of LP anatomic abnormalities by CT should be given sufficient attention by the surgeon.

Materials and Methods

This study retrospectively analyzed 893 patients, including 437 males and 456 females, aged 8 to 87 years old, who received paranasal sinus CT scan in our hospital from February to September, 2020. Patients with a history of facial trauma or sinus surgery were excluded.

The equipment used in this study is a 128-slice-CT scanner (Siemens, imaging parameters: Kv = 120; mA = 120; rotation time, 1.0 seconds; collimation, 128 × 0.6; FoV = 200 mm). Coronal and sagittal images reconstruction (slice thickness = 3.0mm) were performed based on the axial images (section thickness = 0.6 mm). Two investigators (a radiologist and an otolaryngologist) independently completed reading the paranasal sinus CT scans. The cases of LP dehiscence were found and summarized for analysis.

Our study analyzed the incidence of the nontraumatic dehis-cence of the LP. For the positive cases, the severity was further distinguished and graded, the lesion site was located by CT image. We also collected data on misdiagnosis. In addition, the herniation of intraocular muscle was also analyzed.

According to the degree of herniation of the LP, it is divided into 3 grades. Grade I, II, and III refers to the range of herniation involving less than 1/3, 1/3 to 2/3, or more than 2/3 of the LP, respectively. ³

Results

Twenty-three patients were identified with nontraumatic dehis-cence of the LP (2.58%, 15 males, 8 females) as shown in Supplementary Digital Content, Table 1, http://links.lww.com/SCS/D874. No cases of bilateral changes were found. The incidence of left side was 1.34%, and the right side was 1.23%. There was no statistical significance between bilateral incidence. Among positive cases, there were 16 in Grade I (Fig. 1A), 5 in Grade II (Fig. 1B) and 2 in Grade III (Fig. 1C). The average depth of LP ingression was 5.5 ± 0.7 mm (Fig. 1D). As for the location of prolapse, there were 9 cases located in the anterior ethmoid sinus and 3 cases located in the posterior ethmoid sinus. There were 11 cases involving both anterior ethmoid sinus and posterior ethmoid sinus (Fig. 2). In all CT reports, 8 cases were misdiagnosed as ethmoid sinusitis, 9 cases were missed diagnosis, and the remaining 6 cases described the LP ingression. Three cases involving the intraocular muscle were found.

Figure 1.

(A) A male patient (32 years old), Grade I dehiscence of the right LP. No inflammatory changes in ethmoid sinus were involved. (B) A male patient (34years old), Grade II change in the right side. No inflammatory changes in ethmoid sinus were involved. The orbital fat tissue and right medial rectus muscle herniated into the ethmoid sinus. (C) A male patient (60 years old, left chronic maxillary sinusitis), Grade III change of the left LP. The left medial rectus muscle was deformed and herniated. (D) A male patient (60 years old, left odontogenic maxillary sinusitis), Grade II dehiscence. The depth of LP ingression is 7.6 mm on Coronal CT with bone window.

Figure 2.

A male patient (60 years old, left odontogenic maxillary sinusitis), corona CT shows the location of prolapse involving both anterior ethmoid sinus and posterior ethmoid sinus.

Endoscopic nasal surgery was performed in 125 patients. Among the 120 surgical patients without this anatomical variation, LP injury was found in 6 patients, manifested as eyelid ecchymosis, edema and no visual loss has occurred. No orbital complications occurred in the positive cases.

Discussion

The medial orbital wall from front to back is composed of frontal process of the maxilla, lacrimal bone, LP and body of sphenoid bone. The LP is the weakest point (0.2-0.4 mm) of the medial orbital wall, which forms the boundary between the orbit and ethmoid sinus. The LP is prone to occur anatomic variations. ⁴ The LP dehiscence and herniation of the orbital fat and/or intraocular muscle can be caused by trauma, inflammatory lesions, congenital factors, and iatrogenic injury. Age has also been reported to be associated with the morbidity. ^3,5 Dehiscence of the LP is the most common anatomical anomaly, which was observed as early as 1869. ⁶ However, the incidence of this anomaly varies widely. The incidence has been reported as 0.76% to 10.0%. ^1,2 Kitaguchi et al ⁷ reported an incidence of 1.9%. The prevalence of LP defects was 6.5% in a research with 1024 cases. ³ Our study observed 23 cases in a successive series of 893 CT scans of the paranasal sinuses.

The LP dehiscence with herniation of the orbital fat and/or intraocular muscle into the ethmoid sinus was considered as a possible cause of orbital complication in endoscopic sinus surgery. ⁸ Various orbital complications may be caused by surgical injury to the LP, including herniation of orbital fat, strabismus, diplopia, intraorbital hemorrhage, orbital emphysema, and blindness. ⁹ One study involving 483 patients undergoing functional endoscopic sinus surgery showed that the incidence of orbital complications was 2.6% in normal group and 16.7% in the ingression group. ¹⁰ But, the complications such as orbital hemorrhage and limited ocular motility can be avoided without damage to the prolapsed fat. ¹¹ In our research, only 5 patients with LP dehiscence underwent endo-scopic sinus surgery, and no orbital complications occurred. The reasons include the detection of the variation by preoperative CT, the experiences and skills of the surgeon, the use of high-definition display, and intraoperative palpation of the eye to determine whether the medial orbital wall is herniated.

The diagnosis of LP dehiscence was based on a bone defect with orbital contents herniated into the ethmoid sinus on CT. Computed tomography plays an important role in avoiding surgical complications and can detect anatomic variation before operation. By reviewing a series of CT scans, we focused on analyzing the range, depth and location of LP ingression. According to the extent of herniation of the LP, it is divided into 3 grades. ³ We found 16 cases of Grade I, 5 cases of Grade II, and 2 cases of Grade III. In this study, the depth of LP ingression of 23 patients was measured, and the average depth was 5.5 ± 0.7 mm. We also summarized the lesion location through coronal CT scans. The conclusion was that 9 cases were located in the anterior ethmoid sinus; 3 cases were located in the posterior ethmoid sinus. In 11 cases, the lesions spanned the anterior and posterior ethmoid sinuses. The posterior boundary of the LP dehiscence was always the basal lamella, and only the anterior ethmoid was involved reported by a French research. ¹ However, in the present study, these anomalies were not only limited to the anterior ethmoid sinus. The LP ingression may involve the posterior ethmoid sinus as well. Preoperative assessment on CT is helpful for detecting the variation and enhancing surgical safety. We consulted the CT reports and found that there were obvious misdiagnosis and missed diagnosis. So, awareness of dehiscence of the LP is important for clinicians.

There are several limitations that must be acknowledged in the present study. First, 5 patients underwent endoscopic sinus surgery of the entire dehiscence group. Four cases underwent unilateral endoscopic nasal surgery and 1 case underwent bilateral surgery. The average operation time was 69 minutes. Our study did not compare the duration of surgery with negative cases. Comparison of the operative time between the 2 groups can be used to illustrate the impact of this anatomic variation on operative difficulty. Second, the CT images of the surgical cases can be retrospectively analyzed, and the orbital complications in the herniated group and the non-herniated group can be counted, respectively. Last but not the least, we found a lack of recent new findings on anatomic variations of LP. Therefore, this study intends to retrospectively analyze the characteristics of this anatomic variation. The etiology of this variation will be studied and analyzed in our future studies. We hope to further analyze the inpatients undergoing endoscopic sinus surgery, and explore the influence of this variation on the duration of surgery, the amount of blood loss, and the intraorbital complications.

Our study aimed to reveal the characteristics of LP dehiscence via reviewing CT images of paranasal sinus. Adequate preoperative evaluation and digital analysis of the LP variation might decrease postoperative complications and avoid accidental penetration of the LP. Because dehiscence of the LP can be misdiagnosed as inflammation, tumor or fracture and constitutes a high risk for the orbit injury during endoscopic sinus surgery, these findings are of great practical import for treatment planning.