Bitemporal hemianopia
Synonyms and keywords:  Bitemporal hemianopsia

# Overview
Bitemporal hemianopia (bi-: both eyes, temporal: temporal/peripheral, hemi-: half, anopsia: blindness) is defect in visual pathway causing loss of sight in the outer half of the visual field. A lesion compressing or disrupting optic chiasm would result in bitemporal hemianopia. Additional symptoms such as Headache, Diplopia, Endocrine disorders can be present. Most common causes are Pituitary macroadenoma, Craniopharyngioma, Meningioma and Aneurysm of anterior communicating artery. Visual field defects can be diagnosed using Standard Automated Perimetry (SAP). CT Imaging and MRI usually reveal the underlying cause. While vision loss can be improved by treating the underlying cause, sometimes it can be permanent.

# Historical Perspective
- First case of Bitemporal hemianopsia was reported by Clarence A. Veasey, in 1904 .
- In 1929, L.S.Kubie and J.W.Beckmann documented Diplopia to be the most reported symptom in patients with bitemporal hemianopia in the absence of extraocular muscle palsies.

# Classification
- Bitemporal hemianopia may be classified according to the number of defective optic fibers into complete bitemporal hemianopia and partial bitemporal hemianopia.

# Pathophysiology
- Bitemporal hemianopia is a visual defect due to a lesion involving optic chiasm.
- While afferent sensory inputs from superior temporal quadrant of visual field are relayed through inferior nasal fibers of optic nerve, the inputs from inferior temporal quadrant are relayed through superior nasal fibers. Similarly the visual information from superior nasal quadrant and inferior nasal quadrant are relayed through inferior temporal fibers and superior temporal fibers respectively.
- Optic chiasm is an anatomical structure in middle cranial fossa formed by decussation of nasal fibers of optic nerve travelling from retina to visual cortex.
- A lesion involving optic chiasm either due to compression or vascular compromise, disrupts nasal fibers of optic nerve almost always resulting in bilateral defects in temporal half of visual field.
- Nasal fibers have predilection for greater pressure due to compression causing them to be easily disrupted(Mechanical theory).
- A lesion compressing the chiasm from below (eg: pituitary tumors) will have predominant defects in superior temporal quadrants along with partial defects in the inferior temporal quadrant and Vice-versa.

# Causes

## Common Causes
Most of the common causes of bitemporal hemianopia are due to disorders of the pituitary gland and its surrounding structures.
- Pituitary macroadenoma
- Craniopharyngioma
- Meningioma
- Aneurysm of anterior communicating artery

## Causes by Organ System

# Differentiating Bitemporal hemianopia from other Diseases
- Bitemporal hemiaopia must be differentiated from most common causes: pituitary adenoma, suprasellar tumors craniopharyngioma, aneurysm of anterior communicating artery and meningioma.

### Differential diagnosis of Bitemporal hemianopia

# Epidemiology and Demographics
- The prevalence of pituitary adenoma is approximately 16.7% worldwide. Pituitary adenomas are almost always associated with bitemporal hemianopia.
- There is no racial predilection to bitemporal hemianopia.

# Risk Factors
- There are no established risk factors for bitemporal hemianopia.

# Screening
- There is insufficient evidence to recommend routine screening for bitemporal hemianopia in a normal population.
- Patients with asymptomatic pituitary adenomas can be screened by automated perimetry.
- Presence of Vertical step  and Temporal depression is the criteria for diagnosis of bitemporal hemianopia. 

# Natural History, Complications, and Prognosis

### Natural History
- In most of the patients, central visual field of 110120 (using Goldmann perimetry) is preserved and is sufficient for day to day activities. A volume perimetry demonstrates a binocular scotoma beyond the point of fixation.

### Complications
- Shearing of nasal fibers (as in traumatic chiasmal syndrome) most commonly resulted in permanent visual loss and rare improvement.

### Prognosis
- In patients with underlying etiology of pituitary adenomas, an improvement or complete recovery of visual acuity or visual field post-surgery has been seen in 70-75% of cases.

# Diagnosis

## Diagnostic Study of Choice
- The diagnosis study of choice for bitemporal hemianopia is visual field testing.
- Visual field testing by Standard Automated Perimetry(SAP) with favorable sensitivity and early detection is preferred over Goldmann perimetry and is most common method used.
- Even though frequency doubling technolgy (FDT) perimetry has increased sensitivity over SAP, it cannot categorize visual field defects.

## History and Symptoms
- The hallmark of bitemporal hemianopia is the loss of peripheral vision. It is usually an incidental finding as there is no loss in central vision.
- Presence of additional symptoms such as headache, diplopia, endocrine disorders point towards underlying etiology.
- History of chloroquine and ethambutol usage can be present.

## Physical Examination
- Physical examination of patients with bitemporal hemianopia is usually normal.

## Laboratory Findings
- There are no diagnostic laboratory findings associated with bitemporal hemianopia.

## Electrocardiogram
- There are no ECG findings associated with bitemporal hemianopia.

## X-ray
- There are no x-ray findings associated with bitemporal hemianopia.

## Echocardiography or Ultrasound
- There are no echocardiography/ultrasound findings associated with bitemporal hemianopia.
- However, B-scan ultrasonography may be helpful in the diagnosis of bitemporal hemianopia when etiology is Nasal staphylomata.

## CT scan
- Brain CT scan showing a mass near optic chiasm may be helpful in the identifying underlying cause of bitemporal hemianopia.
- Calcifications can be seen in craniopharyngiomas.
- Menigiomas are moderately hyperdense before contrast enhancement and have no or minimal calcification.

## MRI
- Brain MRI showing a mass near optic chiasm may be helpful in the identifying underlying cause of bitemporal hemianopia. Compression of optic chiasm by tumor can be graded from 0-4.
- Extent and the relation of craniopharyngioma to other structures can be clearly seen in MRI than CT scan.

# Treatment

## Medical Therapy
- Even though there is decrease in peripheral vision in bitemporal heminaopia, a central visual field of 110120 is preserved, which is even acceptable for driving licensing.
- Hence, asymptomatic or mildly symptomatic patients and those who aren't suitable candidates for surgery can be treated medically cabergoline for prolactinoma, somatostatin analogues for acromegaly and can be followed up regularly.

## Radiation Therapy
- Radiation therapy can be used as an adjuvant to medical therapy and surgical therapy to prevent remission.
- Gamma-knife therapy has seen a recent success in normalizing hormonal hypersecretion in patients who are not suitable candidates for surgery. A 90.3% tumor control had been achieved in microdenomas.
- Stereotactic radiosurgery is being considered in the treatment of parasellar meningiomas.

## Surgery
- Surgery is the mainstay of treatment for bitemporal hemianopia.
- Pituitary adenoma:
Transsphenoidal pituitary surgery is the first line surgery for pituitary adenomas. Visual improvement occurs in 87% of those with preoperative visual loss. It has a mortality rate of 0.5%.
A meta-analysis of endoscopic vs microscopic surgery hasn't been statistically significant but endoscopic route has been attributed to increased vascular complications.
- Transsphenoidal pituitary surgery is the first line surgery for pituitary adenomas. Visual improvement occurs in 87% of those with preoperative visual loss. It has a mortality rate of 0.5%.
- A meta-analysis of endoscopic vs microscopic surgery hasn't been statistically significant but endoscopic route has been attributed to increased vascular complications.
- Meningioma:
A fronto-orbital approach for tumor excision is preferred. Visual defect has been resolved post-operatively.
- A fronto-orbital approach for tumor excision is preferred. Visual defect has been resolved post-operatively.

## Primary Prevention
- There are no established measures for the primary prevention of bitemporal hemianopia.

## Secondary Prevention
- There are no established measures for the secondary prevention of bitemporal hemianopia.