Neurinoma generates from the cells lining the nerves (Schwann Cells) and is also called Schwannoma. The most frequent intracranial neurinoma is that of the acoustic nerve. It grows in the space called the cerebello-pontine angle. When it is large, it compresses the brainstem and the cerebellum and may cause hydrocephalus. The facial nerve is in deep contact with the tumor (the facial nerve passes in the internal auditory canal with the acoustic nerve). The trigeminal, the abducens and the lower cranial nerves may also be reached by large neurinomas of the cerebello-pontine angle. It is benign and accounts for 7% of intracranial tumors. The presentation ranges from unilateral acoustic deficits to deafness; vertigo and gait disturbances may also be associated. Facial paresis is rare.
Very large neurinomas may be frankly oligosymptomatic.
Contrast-enhanced CT scan and MRI are typical and the diagnosis is easy.

Fig. 5.35: Typical features of a right acoustic neurinoma, frontal MRI view (arrow).
The operation is technically demanding, particularly for large tumors. Intra-operative neuromonitoring of the cranial nerves is mandatory. The structure at risk is the facial nerve. Its identification is not easy. In selected cases, high surgical skills and expertise may permit to spare the hearing function. The operation is done under the surgical microscope; the ultrasonic aspirator is necessary. There are various approaches. The typical neurosurgical approach is the retrosigmoid one. Some otologists are able to operate on cerebello-pontine angle neurinomas with a transpetrosal approach. They report good results, namely in terms of facial nerve function.
As in the case of meningiomas, common-sense rules should be followed for neurinoma patients. Small remnants may be treated with radiosurgery or monitored over time with MRI or CT.
Radiosurgery may also be the treatment of choice for neurinomas smaller than 2.5 cm. The results reported in the latest literature are quite good.
They are benign tumors, similar to their intracranial counterparts. They are a little bit different in histology and may be called neurofibromas. They grow from the nerves within the spinal dura and outside the spinal cord: intradural extramedullary tumors. At times, they follow the nerve outside the spine in a dumbbell shape. They may be multiple. The most frequent location is in the lumbar spine, i.e. the neurofibroma takes origin from one of the nerves of the cauda equina.
Pain is the most frequent symptom; nocturnal pain, relieved in the upright position, is typical. If the spinal cord is compressed, there may be paraparesis or other senso-motor deficits, depending on the level of the lesion. Sphincteric disturbances may be present in large caudal neurofibromas.
Contrast-enhanced MRI is the tool for the diagnosis of spinal neurinomas.
The only therapy is microneurosurgical removal. Like in spinal meningioma, the mininvasive approach is relatively easy in experienced hands. Mininvasive neurosurgery shortens hospital stay, lowers costs, lessens the use of post-operative medication and eliminates the use of post-operative external devices and the risk of late spinal instability.

Fig.5.36: On the left, MRI picture of a spinal neurofibroma at L1 (red arrow); the yellow arrow points to the spinal cord. In the middle, the tumor as seen under the operating microscope, through a mininvasive approach; on the right, the "cauda equina" after tumor removal.