Orbital Tumors - Neurofibroma
Description of Orbital Neurofibroma
- Orbital neurofibroma is a peripheral nerve sheath neoplasm derived from Schwann cells, perineural cells and fibroblasts, and is probably the most common peripheral nerve tumour of the orbit. It constitutes about 0.8 to 3.0% of all histopathologically-proven lesions of the orbit. Orbital neurofibroma produce symptoms within the orbit, and might or might not be associated with systemic neurofibromatosis.
Orbital neurofibroma is classified into three subsets:
- Plexiform neurofibroma is pathognomonic of neurofibromatosis.
- Diffuse nerofibroma has variable association with neurofibromatosis.
- Localized neurofibroma is rarely associated with neurofibromatosis.
Symptoms and Signs of Orbital Neurofibroma
- The presence of multiple painful, well-circumscribed orbital tumours in a patient should raise the suspicion of neurofibroma. Typically, it presents with progressive symptoms of an orbital mass, including proptosis, globe displacement, impaired extraocular motility, ptosis, numbness, and rarely with decreased visual acuity. There might also be associated features of neurofibromatosis. The clinical features of orbital neurofibroma is greatly dependent on its type and associated neurofibromatosis.
- Plexiform orbital neurofibroma: The patient is usually a child in the initially decade of life with undeniable signs of neurofibromatosis, with about 66% having eyelid involvement. It usually begins as an eyelid mass that is more localized to its lateral third, giving the eyelid an S-shaped appearance. It might extend further into the orbit, causing proptosis.
- Diffuse orbital neurofibroma: The patient profile is similar to that of plexiform neurofibroma and usually presents with unilateral proptosis that might or might not involve the eyelids. It’s association with neurofibromatosis is not as strong as in plexiform neurofibroma.
- Localized orbital neurofibroma: The typical patient is a young or middle-aged adult unlike the other forms which present in childhood. Clinical features include a solitary, well-circumscribed soft tissue tumour in the orbit causing proptosis and downward displacement of the globe. Less commonly, it can occur in the lacrimal gland and extraocular muscle, or even cause bony destruction to invade an adjacent sinus.
Diagnosis of Orbital Neurofibroma
- Imaging studies are central to the evaluation of a suspected orbital neurofibroma. Both CT and MRI show smoothly marginated ovoid lesions, with or without lobulations.
- Computerized Tomography: Shows lesions isodense or hypodense to extraocular muscles and shows variable contrast enhancement, with occasional ring-enhancement.
- Magnetic Resonance Imaging: Demonstrates low-moderate T1 signal intensity and moderate-high T2 signal intensity. Heterogeneity of signal strength within the lesion is typical reflecting the mixed histopathology and vascularity of the tumours. Contrast enhancement is again variable.
- Histopathology of a biopsy specimen or excised tumour confirms the diagnosis of orbital neurofibroma.
Treatment of Orbital Neurofibroma
- The management of localized orbital neurofibroma consists of total excision, which is possible in about 46% of cases of isolated orbital neurofibroma. It also has the distinction of low recurrence after surgical excision. However, 72% of postoperative patients reported a sensory skin deficit.
- However, the management of plexiform and diffuse orbital neurofibroma is complex, with an unpredictable outcome. Eyelid sparing orbital exenteration and orbital reconstruction is possibly the best treatment approach in patients with total eyelid ptosis and severe visual loss. Surgery is difficult due to diffuse infiltration and intracranial involvement. Recurrence after incomplete surgical removal is a common phenomenon. Hence, close follow-up is must.