NERVE ROOT TUMOURS
The commonest nerve root Tumours is the benign schwannoma or neurolemmoma, and the most frequent site is the eighth cranial nerve (see vestibular schwannoma). Multiple schwannomas are a feature of neurofibromatosis type 2 (NF2), and schwannomas can occur in the Carney complex, most commonly in the upper gastrointestinal tract and sympathetic nerve chains. Although familial extracranial schwannoma was initially postulated to be allelic with NF2, mutations in SMARCB1 were demonstrated to cause autosomal dominantly inherited central and cutaneous familial schwannomas (Hulsebos et al. 2007). Subsequently, SMARCB1 mutations have been detected in about a half of familial patients and about 10 % of sporadic cases (higher in those with sporadic multiple schwannomas) (Rousseau et al. 2011; Smith et al. 2012). Although familial schwannomatosis was initially defined by the absence of vestibular schwannomas, SMARCB1 mutations have been described in individuals with unilateral vestibular schwannomas and multiple central and cutaneous schwannomas (Smith et al. 2011). In addition, germline SMARCB1 mutations have been reported in patients with a combination of multiple meningiomas and schwannomatosis (van den Munckhof et al. 2012). Germline mutations in SMARCB1 can cause also cause rhabdoid Tumours predisposition syndrome, and very occasionally a SMARCB1 mutation has been associated with both phenotypes (Eaton et al. 2011). It has been suggested that SMARCB1 missense and splice site mutations are preferentially associated with schwannomatosis and deletions and truncating mutations with rhabdoid Tumours predisposition.