Giant spheno-ethmoidal osteoma in a 14-year boy presenting with visual impairment and facial deformity: Short review.

Osteoma located in the paranasal sinus is a slow growing benign tumor. It commonly occurs in frontal, ethmoid and maxillary sinuses in the order of frequency. Giant osteoma is very rare in the pediatric population, and only nine cases of giant osteoma are reported till date in the form of isolated case reports. Authors report a giant spheno-ethmoidal osteoma in a 14-year-old boy, who presented with progressive visual impairment and proptosis of the left eye for last 1-year. Total excision was carried out using transcranial extradural approach. The postoperative recovery was uneventful and showed remarkable visual recovery along with cosmesis.

Introduction

Paranasal sinus osteoma is a slow growing benign encapsulated tumor occurring most commonly in frontal, ethmoid and maxillary sinuses.[1] Small osteoma of paranasal sinuses are often asymptomatic and discovered incidentally on neuroimaging. Osteoma size generally range in 2 mm to 30 mm diameter, osteoma having diameter >30 mm or weight more than 110 g is typically considered a “large” or “giant” osteoma.[1] Giant osteoma of the paranasal sinuses are rare but readily extend into the intraorbital or intracranial cavity, causing serious complications. However, larger osteoma can present with a spectrum of clinical symptoms depending on location.[2] Secondary invasion of the orbits by osteoma is relatively uncommon, with an incidence of 0.9–5.15% of all orbital tumors.[2]

Giant osteoma of the paranasal sinuses are infrequent lesions, especially in the pediatric age group and those of the spheno-ethmoid sinuses are much rarer.[123] We report a rare case of a giant spheno-ethmoid osteoma in a 14-year-old boy with extension into the orbit and optic canal and compression of the optic nerve, causing visual impairment.

Case Report

A 14-year-old boy presented with a history of progressive proptosis with diminution of vision of left eye for 1 year. There was no antecedent history of trauma, chronic sinusitis or nasal surgery. Examination revealed extra-axial proptosis of the left eye in outward and forward direction. Cornea, conjunctiva and anterior chamber were normal. Visual acuity was 6/60 in the left eye and 6/6 on the right side, and fundus showed mild primary optic atrophy on the left side.

Plain computed tomography (CT) scan of the head and orbit showed a bone density mass arising from the sphenoid and left posterior ethmoidal cells, which was extending to the left orbital apex and roof of the optic canal and anterior clinoid process, which was causing compression of the left optic nerve and anterolateral displacement of the optic globe [Figures 1 and 2]. He was planned for surgical intervention.

Figure 1

Computed tomography scan head and orbit, coronal section showed a mass of bone density over sphenoid and left posterior ethmoidal cells with extension to the left orbital apex and optic canal

Figure 2

Computed tomography scan head and orbit, axial section showing mass over sphenoid and left posterior ethmoidal cells with extension to the left orbit

He underwent left frontotemporal craniotomy with combined orbitozygomatic osteotomy using transcranial extradural approach with total excision of a giant osteoma, measuring about 6 × 5.5 × 5 cm [Figure 3]. The excision was accomplished using a high speed drill and osteoma was gradually mobilized from the surrounding thin remodeled bones. At the end of surgical procedure, optic nerve in the optic canal was visualized, with completely thinned out bony canal. He had an uneventful recovery in the postoperative period. He regained visual acuity of 6/12 on the left side on follow-up at 3 months following surgery. Histopathology was consistent with benign cancellous osteoma, which was consisting of trabeculae and fatty bone marrow.

Figure 3

Specimen of sphenoorbital osteoma

Discussion

The distribution of osteoma in the paranasal sinus, according to Mansour et al. includes frontal (71.8%), ethmoidal (16.9%), maxillary (6.4%) and sphenoid (4.9%) sinuses.[2] Osteomas are commonly observed in third to fourth decades of life, with a mean age of 37.8 years.[2] Giant osteomas are rare[123] however, much rarer to occur in the pediatric age group, and only nine cases of giant osteoma originating in ethmoid sinus with extension to the orbit are reported [Table 1].[4567891011]

Table 1

Pediatric giant sphenoethmoidal osteoma with orbital extension

Growth rate of osteoma is variable. Frontal osteoma is slow growing and lobulated and can acquire cauliflower or dumbbell shape causing proptosis in downward and outward direction with rarer intracranial extension. However, ethmoid osteoma is pedunculated, have a propensity to relatively rapid growth and causes proptosis in the outward direction. Sphenoid osteoma is characterized by variable growth rate and shape, causes proptosis in an outward direction and carries high predilection for optic nerve compression and it may cause complete blindness.[35]

Common presenting symptom of paranasal osteoma is localized headache besides nonocular manifestations and sinusitis, frontal mucocele, anosmia, cerebrospinal fluid rhinorrhea and rarely meningitis, brain abscess, and seizures.[235] Ocular manifestations include proptosis, extra ocular muscle displacement, optic disc edema, choroidal folds and orbital infection.[311] Visual loss results from direct pressure on the globe or the optic nerve, or interference with the ocular blood supply, venous drainage, or infection.[312] In long standing cases optic atrophy develops. Blindness is usually unilateral. However, early visual compromise results only with sphenoid osteoma and it even causes primary bilateral optic atrophy.[13]

Osteoma is composed of mature lamellar bones, originate in the bones formed by intramembranous ossification. It can be compact type, which is most common being composed of mature lamellar bone with Haversian systems and containing minimal bone marrow space and X-ray shows rounded sclerotic lesion, while another type called cancellous or spongy type have trabecular architecture with peripheral cortical bone margin. CT scan is the investigation of choice and shows well demarcated hyperdense mass homogenous consistency, may be lobulated, lying on the floor of the sinus causing expansion and distortion of the involved sinus.[28]

Management of osteoma depends on size location, symptoms. Usually observation is advised for asymptomatic osteoma, especially in elderly subjects.[312] Surgery is indicated if osteoma filling of more than 50% of the volume of the frontal sinus, or located near the frontal sinus ostium, extension beyond the confines of sinus or showing enlargement on serial imaging[1581012] other indication for surgical intervention include large osteoma, symptomatic causing headache, recurrent sinusitis, cosmetic deformity, ocular or central nervous system symptoms.

The surgical approach depends on the size, location and extension, minimally invasive surgery including endoscopic method is a choice. However, small osteoma of the ethmoid sinus can be approached through a small external incision around the medial canthus while those of the sphenoid sinus through transseptal, subnasal midline, transpalatal or transorbital transpalate routes.[3] However, giant osteoma as the current case can be removed, and optic canal decompression can be successfully accomplished by the transcranial extradural approach frontotemporal craniotomy with orbitozygomatic osteomy. While selecting transcranial approach, consideration of protection of vital structures, with minimal cosmetic deformity prevails.[3] They can also be approached via the endonasal route with the help of microscope or endoscope.[1]

Conclusions

Sphenoorbital osteomas are rare, but important cause of visual impairment due to optic nerve compression in the optic canal. Current case highlights the importance of early surgery in improving visual outcome.