Bitemporal hemianopia

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-In-Chief:Aditya Govindavarjhulla, M.B.B.S. [2]

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 reveals 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[10][10][10][10][10][10][10]

Causes by Organ System

Cardiovascular	No underlying causes
Chemical / poisoning	No underlying causes
Dermatologic	Dermatochalasis
Drug Side Effect	Chloroquine retinopathy, Ethambutol toxicity
Ear Nose Throat	No underlying causes
Endocrine	Pituatary macroadenoma, Prolactinoma
Environmental	No underlying causes
Gastroenterologic	No underlying causes
Genetic	No underlying causes
Hematologic	No underlying causes
Iatrogenic	No underlying causes
Infectious Disease	No underlying causes
Musculoskeletal / Ortho	No underlying causes
Neurologic	Craniopharyngioma, Aneurysm of anterior communicating artery, Intracranial vascular loop, Meningioma, Enlarged third ventricle, Glioma of third ventricle, Chronic chiasmal arachnoiditis, Suprasellar tumors[17][17][17][17][17][17][17][14][13][13][13][13][13][13], Adamantinoma of sella turcica, Optic neuropathy[13][13][13][13][13][13][13][8][7][7][7][7][7][7], Traumatic chiasmal syndrome, Dolichoectasia of internal carotid arteries
Nutritional / Metabolic	No underlying causes
Obstetric/Gynecologic	Hypophyseal hypertrophy in pregnancy
Oncologic	Adamantinoma of sella turcica, Craniopharyngioma, Glioma of third ventricle, Pituitary macroadenoma, Prolactinoma, Meningioma, Suprasellar tumors
Opthalmologic	Dermatochalasis, Optic neuropathy, Optic chiasmal syndrome, Bilateral blepharoptosis, Traumatic chiasmal syndrome, Retinal disorders, Nasal Staphylomata , Tilted disc syndrome
Overdose / Toxicity	Ethambutol toxicity
Psychiatric	No underlying causes
Pulmonary	No underlying causes
Renal / Electrolyte	No underlying causes
Rheum / Immune / Allergy	No underlying causes
Sexual	No underlying causes
Trauma	Traumatic chiasmal syndrome
Urologic	No underlying causes
Dental	No underlying causes
Miscellaneous	No underlying causes

Differentiating Bitemporal hemianopia from other Diseases

• Bitemporal hemiaopia must be differentiated from Pituitary adenoma, Suprasellar tumors Craniopharyngioma, Aneurysm of anterior communicating artery and Meningioma.
• Differential diagnosis of Bitemporal hemianopia

Pituitary adenoma	No underlying causes
Suprasellar tumors Craniopharyngioma	No underlying causes
Aneurysm of anterior communicating artery	Dermatochalasis
Meningioma	Chloroquine retinopathy, Ethambutol toxicity

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[SN-96% SP-100%] and Temporal depression[SN-100% and SP-98%] is the criteria for diagnosis of bitemporal hemianopia.

Natural History, Complications, and Prognosis

Natural History

• Prognosis is generally good as central visual field of 110°–120° (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.
• 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.
• However shearing of nasal fibers (as in Traumatic chiasmal syndrome) most commonly resulted in permanent visual loss and rare improvement.

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 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 110°–120° 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.

• Meningioma:
  • 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.