Evaluation of Internal Nasal Splint-Supported Free Graft Versus Nasoseptal Flap for Endoscopic Skull Base Repair in Cerebrospinal Fluid Leaks

Cerebrospinal fluid (CSF) leaks are classified as traumatic, iatrogenic, or spontaneous/idiopathic. Traumatic causes include blunt or penetrating facial injuries, while iatrogenic causes stem from neurosurgical or otolaryngologic procedures, such as Functional Endoscopic Sinus Surgery (FESS).

Spontaneous CSF leaks, often linked to elevated intracranial pressure (ICP), may occur in conditions like Idiopathic Intracranial Hypertension (IIH) or due to congenital skull base defects and tumors \[2\]. Risk factors for spontaneous leaks include obesity, female gender, and obstructive sleep apnea, with studies showing 72% of affected patients are female and 45% have sleep apnea.

Benign Intracranial Hypertension (BIH), also known as IIH or Pseudotumor Cerebri (PTC), involves increased brain pressure without structural abnormalities and normal CSF content. Spontaneous CSF rhinorrhea, increasingly prevalent (14-55%), often requires thorough investigations (e.g., fundus examination, CT/MRI, neurological consultation) to exclude intracranial hypertension before endoscopic repair.

Lumbar drain with CSF manometry is reserved for recurrent cases, often due to benign CSF tension increases despite normal preoperative findings. Successful repair requires competent flaps/grafts to withstand CSF pressure during healing. Recurrence necessitates further investigations and may require additional CSF diversion or shunting.

Key steps for successful repair include:

1. Identifying the defect(s). 2. Creating a raw area around the defect by removing mucosa. 3. Precisely placing a graft or flap, optionally sealing dural tears with fat or fascia. 4. Applying adequate pressure to counteract CSF pressure.

Sealing mechanisms involve:

1. Tucking a graft or fat under bony edges or into dural tears, though this may risk dural trauma. 2. Applying a free graft or vascularized flap over the defect and surrounding bone, requiring pressure equal to or greater than CSF pressure. Combining both mechanisms with adequate pressure optimizes sealing and compensates for potential weaknesses.

From a physical perspective, grafts or flaps must exert force equal to or greater than CSF pressure to prevent leaks. On-lay grafts require sufficient force, while under-lay grafts, though challenging, benefit from additional on-lay grafts or flaps to address unnoticed defects.

Nasoseptal flaps (NSFs) have become a widely used technique for endoscopic skull base repair, particularly for cerebrospinal fluid (CSF) leaks. They are vascularized pedicled flaps that provide a robust and reliable option for sealing skull base defects. Studies have shown that NSFs have high success rates, ranging from 90% to 95%, in preventing CSF leaks postoperatively. The vascularity of the flap promotes healing and reduces the risk of graft failure, making it a preferred choice for large or complex defect.

However, NSFs are not without limitations. The technique requires a relatively intact nasal septum, which may not be feasible in patients with prior septal surgery, large septal perforations, or severe septal deformities. Additionally, harvesting the flap can lead to complications such as nasal crusting, septal perforation, and nasal obstruction, which can affect patient quality of life.

Free grafts, such as fascia lata, fat, or synthetic dural substitutes, are another option for skull base repair. These grafts are non-vascularized and rely on the surrounding tissue for nourishment. Free grafts are simpler to harvest and place, making them a viable option in cases where NSFs are not feasible. However, their success rates are generally lower than those of NSFs, with reported success rates ranging from 70% to 85%.

The main challenge with free grafts is their susceptibility to displacement and failure due to the pressure exerted by CSF. Without adequate support, free grafts may not adhere properly to the defect, leading to recurrent leaks. Techniques to improve the stability of free grafts, such as the use of fibrin glue or additional support materials, have been explored, but these methods have not consistently improved outcomes.

The study aims to evaluate the effectiveness of internal nasal splints in improving the feasibility and success rate of free grafts during endoscopic CSF leak repair.