A case of plexiform neurofibroma associated with sphenotemporal dysplasia

Clinical History

A 13-year-old Moroccan female patient presented with complaints of painless progressive swelling around the right eye and right half of the face with protrusion of the right eye since childhood.

Imaging Findings

MRI of the brain and orbits showed dysplasia of the sphenoid and temporal bones. Multiple lobulated ill-defined soft tissue lesions were seen in the right temporal and intraorbital regions. Expansion of the right temporal fossa was also observed. (Fig. 1)
CT of the brain and orbits followed, which showed bone anolamies in greater detail; especially the sphenoid wing dysplasia (Fig. 2, 3).
The diagnosis of neurofibromatosis type1 (NF-1) was made by the association of a plexiform neurofibroma and dysplasia of the sphenoid bone. Furthermore, it is a segmental neurofibromatosis (SNF) according to the classification of Riccardi, because the lesions are strictly unilateral in the absence of a family history or systemic complications.

Discussion

NF-1 (von Recklinghausen disease) is an autosomal dominant genetic disorder, affecting approximately 1 in 3000 individuals [1] with equal distribution between men and women [2].
The diagnosis of NF-I is made when the patient has at least two of the following criteria: at least six café-au-lait spots; at least two neurofibromas of any type or at least one plexiform neurofibroma (PNF); freckling in the axilla or groin; optic glioma; two or more Lisch nodules (pigmented hamartomatous nodular aggregate of dendritic melanocytes affecting the iris); a distinctive bony lesion (sphenoid wing dysplasia or thinning of the cortex of the bones); a first-degree relative with NF-I [1].
Riccardi [3] defined SNF as café-au-lait macules or neurofibromas in a single, unilateral segment of the body, with no crossing of midline, no family history, and no systemic involvement.
SNF is a rare disorder with its prevalence estimated between 0.0014 and 0.002%. It is an example of mosaicism in which localized disease results from a postzygotic NF1 gene mutation located on the proximal long arm of chromosome17 [4].
Orbito-temporal manifestations of NF-1 are characterized by pulsatile exophthalmos, pulsatile enophthalmos, sphenoid wing dysplasia, orbital neurofibroma, expansion of the temporal fossa and herniation of the temporal lobe into the orbit [5].
PNF demonstrate diffuse cylindrical enlargement of multiple fascicles of a nerve including the nerve branches leading to a diffuse mass of thickened nerves. They may be superficial or deep and generally follow the course of the nerves. PNF are benign tumours that tend to grow slowly. Growth spurts are principally seen in early childhood and during puberty or pregnancy.
Sphenoid dysplasia is present in less than 1% of NF-1 patients. In addition, abnormalities of the sphenoid wings are generally considered pathognomonic [6]. Frequently, this manifestation is unilateral. It has been considered as a developmental anomaly of mesodermal origin, but the exact mechanism for the sphenoid bone modifications is unclear. Possible mechanisms include an abnormality in the skull and orbital development, altered transmission of cerebrospinal fluid pulsations and interaction between PNF and sphenoid bone [7].
PNF with diffuse soft tissue infiltration makes complete resection difficult. Recurrent growth may be responsible for repeated surgeries and cosmetic deformity [8].
Classical surgical management of sphenoid dysplasia includes split bone grafting and repair of the anterior skull base defect. A newer option uses a titanium mesh in association with bone graft to serve as a barrier between the orbit and the middle cranial fossa [9].
There are no specific guidelines regarding management for segmental NF. The patient should be informed that they do not have generalized NF 1 and their risk of disease associated complications is low [4].

Differential Diagnosis List

Final Diagnosis

Plexiform neurofibroma associated with sphenotemporal dysplasia

URL:	https://www.eurorad.org/case/12732
DOI:	10.1594/EURORAD/CASE.12732
ISSN:	1563-4086