Neurofibromatosis type 2: proptosis as the initial presentation

Clinical History

A 12-year-old female patient presented with proptosis of the left eye which was gradually progressive over three months. She also had a history of intermittent headache and vomiting. No history of fever, seizure or trauma. She had multiple skin tags on the scalp and trunk. For the past week, she suffered from bilateral tinnitus and hearing loss.
 

Imaging Findings

Bilateral cerebellopontine regions show T1WI hypointense and T2WI heterogeneously hyperintense well-marginated lesions (marked ‘s’) of approximate size 4.0* 2.6 cm (right) and 3.5 * 2.2 cm (left) with mild mass effect. There is widening of bilateral internal acoustic meatuses with intracanalicular extension producing “ice cream on the cone” appearance. (Fig 1, 2) On GRE, blooming black dots represent microscopic haemorrhages. These lesions are vestibular schwannomas. (Fig. 3)

Another T1 and T2 isointense lesion of approximate size 4.2* 4.4 cm is noted in the medial temporal lobe extraaxially (marked ‘m’) without any oedema. This lesion is assumed to be a left sphenoid wing meningioma which extends to the left intraorbital extraconal space (e) possibly through the superior orbital fissure leading to proptosis. Optic nerve and sheath appear normal.

Both schwannoma and meningiomas show intense contrast enhancement. ( schwannoma > meningioma). (Fig. 4, 5). Screening spinal MRI did not reveal any tumours. (Fig. 6)

Based on clinical and imaging findings, a diagnosis of neurofibromatosis type 2 was made.

Discussion

Neurofibromatosis type 2 (NF2) is a neurocutaneous disorder (phakomatosis) characterized by bilateral vestibular schwannomas (VS). It is a rare disease with estimated prevalence of about 1 in 60, 000. It is caused by mutations of the NF2 gene on chromosome 22q12. The NF2 gene encodes for the protein merlin/schwannomin. Half of the cases are inherited (autosomal dominant) and half arise from de novo mutations [1, 2, 3].

The term MISME has been proposed for this syndrome due to multiple inherited schwannomas (MIS), meningiomas (M) and ependymomas (E) [1]. They are usually diagnosed in the second or third decade of life, with a peak in the twenties as compared to NF1. The majority of individuals with NF2 present with hearing loss, which is usually unilateral at time of onset. Other common symptoms include tinnitus, dizziness or imbalance. A significant proportion of cases (20–30%) present with symptoms from an intracranial meningioma (headaches, seizures), spinal tumour (pain, muscle weakness, paraesthesia), or cutaneous tumour. Proptosis is an uncommon presentation as in our case. Cutaneous neurofibromas are absent in NF2. Café -au-lait spots are rare [2, 3]. The skin tag-like lesions in our patient are cutaneous schwannomas.

Four sets of clinical diagnostic criteria have been proposed for NF2 [4, 5]. A definite diagnosis of NF2 is made [according to National Neurofibromatosis Foundation (NNFF) criteria, 1997] when either condition A or B is applicable to the patient
A. Bilateral VS
B. First-degree family relative with NF2 and unilateral VS < 30 years or any two of meningioma, glioma, schwannoma, juvenile lens opacity (posterior subcapsular cataract or cortical cataract).

A fifth set of clinical diagnostic criteria for NF2 has been proposed by Baser. The previous four criteria have a specificity of 100% and a sensitivity of less than 70%. The latest criteria by Baser et al (2011) have a sensitivity of 79% and a specificity of 100%. This system has points for various clinical features and a total score is calculated. A diagnosis of definite NF2 is established if the total number of points is 6 or more.

The most common NF2 related intracranial schwannoma are vestibular schwannomas arising from the inferior division of the vestibular nerve. They present as well-demarcated cerebellopontine angle masses and cause widening of internal acoustic meatus. They are iso to hypointense on T1 and iso to hyperintense on T2 weighted images and show intense and homogenous enhancement. Trigeminal and occulomotor nerve schwannomas can also occur. Meningiomas are present in half of the cases, usually multiple and can be present in brain and spine. The majority of intramedullary spine tumours are ependymomas and arise in either the upper cervical cord or the conus [2, 3, 6].

Teaching point:
Bilateral vestibular schwannomas are diagnostic of Neurofibromatosis type 2 without the need for biopsy. Proptosis can be an uncommon presentation.

Differential Diagnosis List

Final Diagnosis

Neurofibromatosis type 2

URL:	https://eurorad.org/case/13729
DOI:	10.1594/EURORAD/CASE.13729
ISSN:	1563-4086