Brown syndrome is a vertical strabismus syndrome characterized by limited elevation of the eye in an adducted position, most often secondary to mechanical restriction of the superior oblique tendon/trochlea complex.
Previously referred to as "superior oblique tendon sheath syndrome," it was considered a dysgenesis of the superior oblique muscle's tendon sheath. More recently, it is thought that the problem is not the sheath, but rather the tendon itself, that undergoes increased tension.
Brown syndrome can be congenital or acquired, is unilateral in 90% of patients, and has a slight predilection for females. There is thought to be a genetic predisposition to congenital Brown syndrome, however, most cases are sporadic in nature.
Based on the 9-gaze pattern, it can be confused for an inferior oblique palsy. Differentiation between IO palsy and SO restriction of Brown’s can be done using Forced Duction Test. As it is a painful test, it is difficult to perform in children without general anesthesia.
Fundamentally, Brown syndrome results from a limitation of the normal function of the superior oblique tendon-trochlea complex. It most often occurs as a congenital condition. Various theories have been suggested for the pathogenesis of Brown's syndrome. It has been proposed that congenital Brown syndrome is due to a dysgenesis of the muscle tendon, superior oblique tendon sheath or trochlea, and recent work suggests that some cases may be associated with congenital cranial dysinnervation disorders.
There is a large differential for secondary causes of Brown syndrome, including inflammation, trauma, tendon cysts, previous sinusitis, orbital tumors, and iatrogenic causes such as orbital or strabismus surgery. Abnormalities of the fascial anatomy is considered to be a rare cause. For uncertain reasons, Brown syndrome is more commonly found in the right eye than the left eye.
The diagnosis of Brown Syndrome is based on the clinical findings and history. Further workup may be needed in acquired Brown syndrome and often depends on the suspected underlying etiology. For example, workup for a suspected inflammatory etiology may require laboratory testing, while suspected trauma may prompt additional imaging.
A complete ophthalmic examination should be performed. Special focus should be given to the sensory-motor examination, including strabismus measurements in all cardinal positions of gaze, ocular motility, and binocular function/stereopsis. In cases of acquired Brown syndrome, a thorough orbital examination should be performed with special attention to the trochlear area.
The key finding in Brown syndrome is limited elevation in AD-duction. Limited elevation in straight-up gaze and abduction can also be present, but are more subtle. In mild cases, there is no vertical deviation in primary position or downshoot in adduction. In moderate cases, there is no vertical deviation in primary position, but there may be a downshoot in adduction. In severe cases, there may be both a hypotropia in primary position and downshoot in adduction. A compensatory abnormal head position may be present, often patients adopt a chin up position or a head turn away from the affected eye (to keep the affected eye abducted, avoid hypotropia, and promote binocular fusion).
Forced duction testing is very useful in the diagnosis of Brown syndrome, and will demonstrate restriction to passive elevation in adduction.
Amblyopia is generally absent. A down movement of the eye on adduction may mimic superior oblique over-action with or without associated IO plasy. However, a characteristic V-pattern (divergence on upgaze) will be noted in Brown syndrome, in contrast to the A-pattern (divergence on down-gaze) seen in superior oblique over-action with or without associated IO plasy. Saccadic eye movements should remain unaffected in contrast to Superior Oblique Myokymia (SOM).
A tendon cyst or a mass may be palpable in the superonasal orbital. Brown Syndrome secondary to an inflammatory condition is frequently associated with orbital pain and tenderness on movement or palpation of the trochlea.
Patients with Brown syndrome may have a variety of symptoms which may be constant, intermittent, or recurring, including:
- Poor binocular vision/stereopsis
- Orbital pain and tenderness
- Pain with eye movement
- Abnormal head position
- A ‘click’ may be heard or felt by the patient with movement of the eye when attempting to elevate the eye in AD-duction
Brown syndrome should be differentiated from the following conditions:
- Inferior oblique muscle palsy
- Superior oblique over-action
- Double elevator palsy
- Congenital fibrosis of extraocular muscle
- Thyroid eye disease
- Orbital fracture with entrapment
- Myasthenia gravis
Management of Brown syndrome depends on symptomatology, etiology, and the course of the disease.
Observation is often preferred, as symptoms are often intermittent in nature and do not cause permanent damage. Improvement of congenital Brown syndrome has been described in up to 75% of cases. Of note, as patients are most symptomatic on upgaze, normal growth can decrease symptoms as patients grow taller and have less necessity for upgaze position. Acquired Brown syndrome cases may also undergo spontaneous resolution, and thus early surgical intervention is not recommended.
Brown syndrome due to inflammatory disease with associated pain may transiently benefit from injection of steroids to the trochlear area. This may require recurrent treatments for symptomatic relief.
Systemic steroids and non-steroidal anti-inflammatory agents have also been utilized with variable success. Immunosuppressants (i.e. adalimumab) have been used in refractory cases.
Surgery can be considered in the following circumstances:
- Hypotropia in primary position
- Significant abnormal head position
- Significant diplopia
- Significant downshoot on adduction
- Compromised binocularity
- Significant orbital pain or pain with eye movements
The following surgical procedures can be performed:
- A tenotomy or tenectomy to weaken the superior oblique (but beware post-operative iatrogenic superior oblique palsy)
- A superior oblique expansion surgery has been found to have high success rates and can be performed through a variety of techniques, including a silicon expander (e.g. a #240 retinal silicone band), a non-absorbable "Chicken suture", or a superior oblique split tendon lengthening procedure
- Iatrogenic Brown syndrome secondary to muscle plication may require reversal of the plication
- In case the primary cause is a tendon cyst, removal of the cyst may be indicated
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