The Ophthalmology Unit,  Universiti Malaysia Sarawak (UNIMAS), Kuching, Sarawak.
The Ophthalmology Department, Sarawak General Hospital, Kuching, Sarawak, East Malaysia.
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aCase 15 Answers

by Dr.Chua and Dr. Tay1

 

1. Head of Dental Department, Sarawak General Hospital, Kuching, Sarawak.


A 58 year-old man presented with a right progressive ptosis of two-year duration and a solid hard mass arising from the roof of the anterior orbit. He had no past medical history of note. He also suffered from diplopia on upgaze. His vision was  6/6 in both eyes and palpation confirmed the presence of the lesion extending from the medial half of the orbit to the medial wall. Ocular movement is full except on up-gaze.


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Figure 1 and 2. Right ptosis with fullness of the superior sulcus.

            Mild restriction of the right eye on upgaze.

 

 

A CT scan of the orbit revealed the following features suggesting of frontal and ethmoidal osteoma. Surgery was planned for excision of the lesion.

 

Figure 3 A-D. CT scan of the right orbit showing the presence of right frontal and ethmoidal

osteoma. The lesions are hyperdense as the bone.

a. What is the nature of these lesions?

Osteoma is the most common tumour of the bones of the orbit. The true incidence is unknown as the vast majority are asymptomatic. They have been noted in just under 1% of patients undergoing sinus radiographs. The aetiology is unclear and several risk factors have been put forward including trauma and infection.

They tend to develop at the junction of membranous and endochondral bone and commonly found in the frontoethmoid complex. They may continue to grow throughout life but the growth is maximal during the period of skeletal development.

Histologically, they can be divided into:

  • compact variety with dense lamellar bone with no haversian system or marrow cavities (as in this case).

  • spongy variety which is predominantly cancellous with fatty marrow.

  • mixed variety.

They can grow to considerable size before causing symptoms from distortion of structures such as the orbit. Osteomas have also been reported in 14% of patients with Gardener's syndrome.

The treatment of choice is surgical but this should only be undertaken if it is symptomatic. Recurrence is uncommon.

 

b. How can the lesion be approached and state the advantages and disavantages of each approach?

Two approaches may be used:

a. Frontotemporal approach. In this method, a bicoronal incision is made. The frontalis and temporalis are then reflected off the skull. The periosteum is then free to expose the osteoma. This method has the advantage of greater exposure and preservation of the supraorbital nerves and vessels. However, this patient is bald so the resulting scar can not be hidden by the hair.

b. Direct approach via anterior orbitotomy. Compared with frontotemporal the expsoure is less (especially if the lesion were to extend posteriorly) and the patient may experience forehead anaesthesia due to resection of the sensory nerves. The advantages of this approach is that the lesion can be reached directly and the scar minimal especially if skin crease approach is chosen.

In our patient, a skin crease approach was used to minimize scarring (see Figure 4). Dissection is made between the orbicularis and the orbital septum to expose the frontal periosteum. Vascular bundles were identified and cauterised. Incision of the periosteum is made with a No 15 blade and the periosteum is reflected away from the osteoma. Drill holes were made along the superior and medial edges of the osteoma and chisel used to remove the lesion. The roof and the edge of the superior orbit was drilled to remove the osteoma and also to smooth the surface. The periosteum and the skin crease were sutured. At one-week follow-up, the ptosis remained and the patient complained of diplopia and on examination showed supeior oblique palsy. We believe the ptosis and the diplopia will improve with time. There was only minimal hypoanaesthesia of the forehead.

Figure 4. Skin crease incision for anterior orbitotomy in the removal of the frontal

osteoma.

References:

1. Gershwin ME, Incaudo G Diseases of the Sinuses: A Comprehensive Textbook of Diagnosis and Treatment.   Humana Press Inc.,U.S.

2.  Cokerham KP, Bejjani GK, Kennerdell JS, Maroon JC. A reappraisal of surgery for orbital tumors. Part I: extraorbital approaches. Neurosurg Focus 10 (5) Article 2, 2001.

3. Cokerham KP, Bejjani GK, Kennerdell JS, Maroon JC. Surgery for obrital tumors. Part II : transorbital approaches. Neurosurg Focus 10 (5) Article 3, 2001.

 

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