Computed tomography of lesions of the optic nerve.

Computed tomographic (CT) findings in 25 patients with various optic nerve lesions were reported. Neoplasms of the optic nerve/sheath particularly optic nerve gliomas and sheath meningiomas were found to be the major causes of the enlargement of the optic nerve in this series. Optic nerve gliomas is the most common lesion in children while the sheath meningioma usually occurs in adult. CT appearance of these tumours can appear as uniform thickening or uniform enlargement of the entire nerve. However, differentiation between the two tumours can be made by contrast enhancement. Enhancement of optic nerve sheath meningioma on CT is usually more marked than optic canal is also pathognomonic railroad track appearance is often identified. Typical hyperostosis around the optic canal is also pathognomonic for meningioma. Other tumours especially lymphomas, leukaemia and carcinomas of paranasal sinuses and nasopharynx can produce enlargement of the optic nerve/sheath by infiltration or direct compression to the nerve. In addition, nonneoplastic processes such as optic nerve/sheath on CT. Certain clinical and computed tomographic features permit distinction of these non-neoplastic conditions from tumours.

Computed tomography in differential diagnosis of enlarged extraocular muscles.

Computed tomographic (CT) findings in 50 patients with various orbital lesions causing enlarged extraocular muscles were repoeted. Graves’ ophthalmopathy was the most common cause of bilateral exophthalmos. Extraocular muscle enlargement was found to be bilaterally symmetrical in 25% of the patients. In 75% of the patients, the lesion was asymmetrical either unilaterally or bilaterally. Medical and lateral rectus muscles were most frequently involved and medial rectus muscles was the most severely affected. Pseudotumour was commonly unilateral. The involved muscle was less regular than in Graves’ disease. It tended to involve single muscle. The site of involvement was in the region of the posterior globe at the muscle insertion. Associated findings, such as infiltrative change in adjacent fat, lacrimal gland involvement and thickening of the optic nerve may help in diagnosis. Carotid-cavernous fistulas and dural arteriovenous malformation can cause the enlargement of extraocular muscles or compress the muscle origin and their venous drainage causing muscle enlargement. In addition, orbital infection and trauma can involve the muscles by the process of inflammatory infiltration, swelling and haemorrhage respectively. CT was proved to be the best radiologic means for the diagnosis of enlarged extraocular muscles and their causes.

Computed tomography in the diagnosis of orbital pseudotumor.

Eighteen patients with orbital pseudotumor were analysed. These patients were admitted into Siriraj Hospital during 1981 to 1985. They were 12 males and 6 females ranging in age from 5 to 75 years. Orbital pseudotumors are nonspecific influammatory lesions of unknown aetiology which may affect part or less frequent, al of the tissue within the orbit. Computed tomographic (CT) study of 18 patients demonstrated that these lesions could be unilateral or bilateral. In 5 patients (28%) with bilateral orbital pseudotumour, the lesions were multifocal and involved several orbital structures (globe, optic nerve, extraocular muscles and lacrimal gland). However, they could be differentiated from Graves’ opthalmopathy. In 13 patients (72%) with unilateral pseudotumour, the lesions could be classified into five anatomic patterns: anterior, posterior, diffuse, lacrimal and myositic. The diffuse and isolated discrete mass lesions of orbital pseudotumour, sometimes can not be differentiated either from other infiltrative conditions as lymphoma or leukaemia or from other neoplasms within the orbit. Scleral uveal rim thickaening with contrast enhancement was found only in 3 patients (17%) with pseudotumour. This sign is not characteristic for orbital pseudotumour but it represents nonspecific inflammation of the globe. Orbital CT is not only an excellent technique in detection of orbital pseudotumour but it is also useful in the follow up of cases after treatment as well.

The hangman’s fracture.

Eleven patients with hangman’s fracture admitted into Siriraj Hospital Between 1978 and 1984 were studied and analysed. Automobile accident (73%) and falling (18%) were the most common causes of this injury. The mechanism of the injury was acute hyperextension of the head on the upper cervical spinal. Because the fracture occurring at the greatest anteroposterior diameter of the cervical spine canal, the spinal cord injury was rarely associated with this lesion. Radiographic findings of the hangman’s fracture were bilateral fracture of the pedicles of the axis with or without anterior dislocation of C2 on C3. The degree of displacement varied from minimal to severe. However the posterior fragment usually retained its normal relationship to the posterior arch of C3. Retropharyngeal soft tissue swelling served as a general clue to the presence of this injury and an avulsion fracture or compression of the anterosuperior margin of the body of C3 was an additional finding of the lesion. Differential diagnosis of the hangman’s fracture should be made from the congenital spondylolisthesis of the axis.

Acute cervical spine injury.

Ninety eight patients with cervical spine trauma were analysed. They were 78 males and 20 females ranging in age from 6 to 78 years with an average of 35.4 years. These patients were admitted into Siriraj Hospital during 1977 to 1984. The automobile accident appeared to be the most common cause of cervical spine injury, found in approximately 63% of the cases. The cases of cervical spine trauma were classified on the basis of mechanism of injury and all these patients had radiographic examinations which were studied in detail. Flexion type of injury was found in 42% of the patients had was the most common type of injury. Cervicocranial injuries were found in 29% of the patients and were the next most common occurrence. Vertebral body and vertebral arch were the most frequent sites of the injury while the distribution of the injuries by the level tended to occur quite commonly in lower cervical segments. Among these patients, there were 69 patients (70%) with neurological deficit. Radiographic feature of all types of cervical spine injuries is discussed in detail and the useful radiographic examination of the cervical spine in the emergency room is recommended.

Fractures of the dens (odontoid process): A report of 23 cases.

Twenty three patients with natures of the dens admitted into Siriraj Hospital during the past seven year were studied and analysed. Traffic accidents (74%) and fall (22%) caused the majority of the dens fractures. These fractures were classified into three types based on the anatomic location of the fracture line. Three patients with type I (avulsion), 16 patients with type II (involving the body) and 4 patients with type III (basilar) fractures of the dens are reported. Types II fractures appeared to be the most common. They were unstable and easy to displace. Severe hyperflexion and hyperextension during the accidents caused the anterior and posterior fracture–dislocations of the dens respectively. Anterior fracture–dislocations was found to be more frequent. Patients with dens fractures may have less or no neurological deficit. Mach bands can cause confusion in the roentgen diagnosis. Differential diagnosis of the dens fracture should be made from or odontoideum.