General Medical Information

Neurogenic Tumors

Sharen J. Knudsen
Byron J. Bailey

Neurogenic tumors are best classified according to embryonic cells of origin. These benign tumors encroach on the nasal framework and distort the anatomic configuration of the nose. Early removal is advised, and successful treatment necessitates knowledge of embryonic anatomic relations. The anterior wall of the developing nose is cartilaginous. In front of this cartilage, the nasal and frontal bones develop within a mesenchymal layer. The frontal bones initially are not fused, and the space between them is called the fonticulus frontalis. The prenasal space exists between the nasal bones anteriorly and the cartilage posteriorly. Dura can project into this area through the foramen cecum at the base of the frontal bone. In normal development, this dural canal is obliterated. Any defect in this process leaves a pathway for neural tissue to extend to the prenasal space close to the nasal skin. The incidence of these disorders is estimated at 1 in 20,000 to 40,000 live births.

Nasal glioma is a rare lesion at the bridge of the nose near the midline. Sixty percent of nasal gliomas are extranasal, and 30% are intranasal. The lesion is characterized by a rounded, skin-covered, nonpulsatile, firm mass. Glioma does not become larger with crying or straining. Intranasal glioma can appear as a polyp in the mouth, nasopharynx, or pterygopalatine fossa. The growth rate varies considerably. Boys are more commonly affected than are girls. Treatment is surgical excision. A CT scan is mandatory in the preoperative evaluation to rule out intracranial extension, and a biopsy of nasal polyps may show glial tissue. An intranasal approach suffices for small lesions, and extranasal combined approaches are used for operations on larger intranasal and all extranasal lesions. Frontal anterior craniotomy may be needed for operations on lesions with intracranial extension. Children with nasal glioma have been treated successfully by means of transnasal endoscopic resection of the glioma with immediate repair of the skull-base defect with a free mucosal graft, pedicled mucosal flap, or conchal cartilage with fibrin glue and nasal packing for 3 weeks.

Encephalocele is structurally different from glioma because it contains an ependyma-lined space that contains cerebrospinal fluid (CSF) and communicates directly with the ventricles. Meningocele contains meninges; meningoencephalocele contains meninges and brain; and meningoencephalocytocele contains meninges, brain, and part of the ventricular system. Encephaloceles grow larger with crying and straining. Compression of the jugular veins, with a resultant increase in CSF pressure, produces enlargement of the mass, known as a positive Furstenberg test result. Encephalocele looks like glioma, except that it can be transilluminated. There is always a bony defect. Encephalocele is five times more common in the lumbosacral area than in the cranium. Of those in the cranium, 75% are located in the posterior occipital area and 25% in the anterior area.

Sincipital encephalocele involves the frontoethmoid area and is external. The bony defect is anterior to the crista galli in the region of the foramen cecum. Basal lesions manifest themselves internally. The skull defect is in the floor of the anterior cranial fossa between the cribriform plate and the clinoid process or through the superior orbital fissure. Magnetic resonance imaging (MRI) is considered more valuable than CT scanning because the soft-tissue structures are better delineated without exposure to ionizing radiation. Treatment involves complete closure of the dural defect to prevent CSF leaks and excision of irreducible herniated brain tissue. A large defect necessitates a dural graft. Complications of surgery include meningitis and CSF leak.