Endoscopic Surgery of the Paranasal Sinuses and Anterior Skull Base
The current techniques applied at the Skull Base Institute, have allowed routine endoscopic management of benign and malignant sinonasal tumors and their extensions into the anterior skull base and the orbits. Our minimally invasive endoscopic approaches avoid facial incisions, osteotomies, and tracheostomies.
In most cases the surgery is performed entirely through one nostril with no skin incisions using a fully endoscopic approach. This less invasive surgery results in shorter recovery times, more aesthetically pleasing results, and a smoother postoperative course without sacrificing outcomes and with fewer complications. Occasionally, for tumors with significant extensions through the skull base, the endoscopic transnasal approach is combined with an endoscopic supraorbital approach which allows a panoramic exposure of the intracranial extension of these tumors.
There are four paired paranasal sinuses within the skull, all four sinuses drain into a specific area in the nose called the "osteomeatal complex". The paranasal sinuses have close anatomical relations with the orbits and the skull base and many tumors that arise in the paranasal sinuses may invade these structures and have intracranial or intraorbital extensions. Additionally, the paranasal sinuses often serve as "anatomical passages" when performing skull base surgery.
The frontal sinuses - located above the base of the nose
The ethmoid sinuses - located just behind either side of the upper nose
The sphenoid sinuses - located behind the ethmoid sinuses at the center of the skull base
The maxillary sinuses - located under the eye sockets and in the upper part of either side of the upper jawbone
Approximately 3% of all malignant tumors of the upper respiratory tract arise in the nose and the paranasal sinuses, with 59% of such tumors involving the maxillary sinuses; 24%, the nasal cavities; 16%, the ethmoid sinuses; and less than 1% involving the sphenoid or frontal sinuses.
Types of paranasal sinus tumors
The most common malignant neoplasm of the paranasal sinuses is squamous cell carcinoma, occurring in 70-80% of all cases. Regional node involvement from primary squamous cell carcinoma of the paranasal sinuses occurs in about 15% of all cases and nodal spread and distant metastasis occur in approximately 9% of all cases. Other malignant tumors of the paranasal sinuses that occur less frequently are adenoid cystic carcinoma, mucoepidermoid carcinoma, malignant mixed tumor, adenocarcinoma, melanoma, lymphoma, fibrosarcoma, osteosarcoma, and chondrosarcoma.
These neoplasms grow within the bony confines of the paranasal sinuses and often are asymptomatic until they erode or invade adjacent structures. Commonly, paranasal sinus tumors are slow growing with a low tendency to spread (metastasize) locally, regionally or distantly. The most common malignant neoplasm arising elsewhere and metastasizing to the paranasal sinuses is hypernephroma. Other metastatic lesions include undifferentiated tumors arising from the lung, breast, prostate, and pancreas.
Glandular malignancies (adenocarcinomas) may arise from either minor salivary glands or from the basal lamina of the respiratory epithelium. The salivary glands are divided into the major glands (parotid, submandibular and sublingual) and minor glands (found in the submucosa of the nose, sinuses, mouth and upper aerodigestive tract). Adenocarcinomas account for 10-20% of all primary malignant neoplasms of the nasal cavity and paranasal sinuses. Adenocarcinomas have the propensity for perineural spread via the infraorbital nerve and have been known to cause bilateral orbital invasion with blindness. In general, tumors arise more frequently in the major glands with the parotid gland being the most common site. Fortunately 70-80% of these tumors are benign mixed tumors or pleomorphic adenomas of the parotid. Although minor salivary gland tumors are less common, approximately 60% of them are malignant.
The most common benign neoplasm of the paranasal sinuses is squamous cell papilloma; papillomas are benign growths but may sometimes undergo malignant degeneration. Less frequent benign tumors of the paranasal sinuses include fibromas, neurilemomas, ossifying fibromas, and osteomas. Osteomas are noted more commonly in the frontal sinus or anterior ethmoid regions and may block the nasofrontal duct, producing frontal siunusitis.
Another benign lesion of the paranasal sinuses that can lead to intracranial extension is a mucocele. This is a mucus-containing cyst that occurs within the sinus, usually resulting from the trapping of mucus-producing sinus lining by trauma or infection. These cysts are commonly seen in the maxillary sinuses but may also occur in the ethmoid, sphenoid, or frontal sinuses. They can result in erosion of the surrounding bony walls with extension into the orbit, the soft tissues of the frontal area, or the cranial cavity through the roof of the ethmoid complex or the posterior wall of the frontal sinus. If these cysts become infected, then they are termed mucopyoceles. They are accompanied by more rapid erosion of the surrounding bony walls and increased chances of orbital or intracranial infection.
Mucoceles may present with symptoms of chronic frontal, vertex, or occipital headache associated with a history suggestive of chronic rhinosinusitis. They may also present with ocular proptosis and soft tissue swelling. Posterior frontal sinus wall erosion may result in meningitis or epidural, subdural, or brain abscess. Sphenoid and posterior ethmoid mucoceles are less frequent and may present with orbital involvement resulting in decreased vision, exophthalmos, diplopia or with the superior orbital fissure syndrome consisting of ocular palsies and decreased forehead sensation.
The cause of paranasal sinus neoplasms is unknown, however, some clinical data indicates that various industrial exposures may be related to cancer of the paranasal sinuses and nasal cavity, these risk factors include exposure to nickel, chromium, mustard gas, isopropyl alcohol, radium; and possibly chronic sinusitis. Benign squamous cell papillomas are thought to be caused by papovaviruses. Adenocarcinomas arising from the ethmoid or maxillary sinuses are frequently associated with exposure to industrial wood dust in the hardwood and shoe industries workers.
The symptoms of paranasal sinus tumors vary with its specific type, location, and stage. Symptoms typical of early lesions often resemble those of an upper respiratory tract infection and include nasal obstruction, facial pain, and thin, watery nasal discharge which can at times be blood-tinged. The key factor that differentiates the symptoms of an upper respiratory infection from a paransal sinus tumor or malignant lesion is the duration of the symptoms, which in the latter are persistent.
The most common symptoms of paranasal sinus cancers include:
Nasal: A persistently blocked nose or bleeding per nose (epistaxis)
Oral: loose teeth or dentures, bleeding from upper teeth sockets, swelling in the roof of the mouth, oral pain, or trismus
Ocular: closing up of one eye, blurred vision, double vision (diplopia), proptosis, or visual loss
Facial: paresthesias, asymmetry, progressive pain and/or swelling of the face or around the eyes
The diagnosis of nasal and paranasal sinus cancers is usually made late because early symptoms of such cancers are similar to those found in patients with acute and chronic sinusitis. Frequently, tumors arising in the maxillary sinus have spread to the ethmoid sinuses, cribriform plate, and orbit by the time a diagnosis has been made. Tumors arising in the ethmoid, frontal, and sphenoid sinuses are less common; however, intracranial or orbital involvement is frequently seen at the initial presentation.
Radiographic images reveal a shadow density within the involved paranasal sinus, usually associated with thinning or outward bulging of the surrounding bony walls, suggesting an expanding lesion. The appropriate preoperative imaging evaluation methods include computed tomography (CT) scans using intravenous contrast administration and bone windows to detect early lesions and note any bony destruction, orbital or intracranial extension. Magnetic resonance imaging (MRI) scans are also performed as MRI is particularly useful in detecting intracranial extension of the paranasal sinus neoplasm and distinguishing certain specific neoplasms.
Following radiographic evaluation, tumors may be biopsied prior to definitive evaluation and treatment. This can optimally be performed in the operating room, especially when exploration of the involved sinus is required.
The optimal treatment of expanding neoplasms and mucoceles of the paranasal sinuses is surgical removal. The specific approach is determined by the location and appearance of the lesions. Malignant tumors originating from the paranasal sinuses will require radical resection with wide margins including any intraorbital or skull base extensions. Postoperative radiation therapy often accompanies surgical resection. Clinical data has proven that combining chemotherapy (either intra-arterial or intravenous) with radiation therapy for paranasal sinus tumors may also improve local control.
Traditionally, numerous approaches have been described for resection of paranasal sinus tumor including lateral rhinotomy, transoral/transpalatal and midfacial degloving. Tumors with extensive spread or tumors of the ethmoids and frontal sinuses with involvement of the skull base have traditionally required a combined craniofacial approach, including resection of the floor of the anterior cranial fossa.At the Skull Base Institute endoscopic minimally invasive techniques have replaced these traditional aggressive approaches.
The importance of accurate pretreatment evaluation and staging with paranasal sinus tumors is critical, the stage and type of the paranasal sinus tumor are the most important factors in determining the prognosis. In general, survival rates have markedly improved because of advances in skull-base surgery and cure rates of up to 80% are attainable with early-stage tumors that are completely excised. Follow-up must be frequent and meticulous especially during the first two years following treatment as these carry the highest rate of local recurrence. Lifetime follow-up is often necessary.