Optic Chiasm and Pituitary Anatomy Quiz

Optic Chiasm

• 25% of brain tumors occur in the chiasmal area of the thalamus.
• Approximately 50% of these tumors present with initial visual loss complaints.

Anatomy: Chiasm & Pituitary

• The pituitary gland is situated within the sella turcica of the sphenoid bone.
• The diaphragma sellae is a layer of dura mater.
• The optic chiasm is positioned about 10mm above the diaphragma sellae.
• Measurements:
  • 15mm
  • 8mm
  • 4mm
  • 45°
  • 10mm

Position of Optic Chiasm

• Central (80%): The chiasm sits directly above the pituitary gland.
• Prefixed (10-16%): The chiasm sits in front of the pituitary gland; affects the chiasm and optic tracts.
• Postfixed (4-10%): The chiasm sits behind the pituitary gland; affects the chiasm and optic nerves.

Etiologies of Chiasmal Compression

• Pituitary tumor (50-55%)
• Craniopharyngioma (20-25%)
• Meningioma (10%)
• Glioma (7%)
• Aneurysm (rare)

Pituitary Adenoma

• Headache
• Blurred vision (vague)
• Visual field (VF) defects
  • Bitemporal(superior > inferior)
  • Junctional scotoma
  • Incongruous homonymous hemianopia
  • Diplopia
  • "hemi-field slide"
• Two groups:
  • Nonfunctional (non-secreting): accounts for 40%, 70% macroadenomas cause visual loss.
  • Hormone hypersecretion: prolactinomas and Growth Hormone are most common.
• Radiological features:
  • Macroadenoma protruding into the sphenoid sinus.
  • Thin bone of the floor or non-existent.
  • Enlarged, asymmetrical sella turcica.

Pituitary Adenoma: Treatment

• Surgery: trans-sphenoidal
• Radiation: Gamma Knife, Proton Beam.
• Medical therapy: Bromocriptine, Octreotide

Pituitary Gland: Hormones

• Anterior Pituitary:
  • Adreno-corticotropic hormone (ACTH)
  • Growth Hormone (GH)
  • Melanocyte Stimulating Hormone (MSH)
  • Thyroid Stimulating Hormone (TSH)
  • Gonadotropins (FSH, LH)
  • Prolactin
• Posterior Pituitary:
  • Oxytocin
  • ADH

Prolactinoma

• 35% of all pituitary tumors.
• Secretes prolactin 100–1000x normal levels.
• Women: amenorrhea, galactorrhea, infertility
• Men: decreased libido, impotence, infertility, hypopituitarism, galactorrhea, gynecomastia.
• Treatment (1st line): Bromocriptine, Cabergoline

TSH-Secreting Adenoma

• Rare; ~50% with VF defects.
• Two types:
  • Primary hypothyroidism leads to hyperplasia of pituitary thyrotroph cells and enlarged pituitary gland.
  • TSH-secreting tumor leads to thyrotoxicosis—high circulating levels of T3 and T4.
• Thyroid Ophthalmopathy is rare.

GH-Secreting Adenoma

• Secretes excess growth hormone.
• Adults: acromegaly (enlarged hands/feet, lower jaw/tongue, coarsened facial features).
• Children: gigantism.
• Associated symptoms: hyperthyroidism, diabetes, arthritis.

ACTH-Secreting Adenoma

• Secretes excess ACTH.
• Hormone responsible for cortisol production.
• Cushing's disease:
  • Truncal obesity
  • Thin skin and purple striae
  • “Moon face”, “Buffalo Hump”
• Small tumors.
• Rarely cause chiasmal compression.

Pituitary Apoplexy

• Spontaneous, rapid pituitary gland expansion (infarction or tumor).
• Neuro-ophthalmic emergency.
• Symptoms:
  • Sudden and severe headache
  • Visual loss/visual field deficits
  • Diplopia
  • Nausea, vomiting
• Often occurs with pituitary tumors; ~80% do not know they have pituitary tumor.
• Sheehan's syndrome.

Craniopharyngioma

• ~3% of intracranial tumors; 13.5% of CNS tumors in children.
• Derived from pituitary gland embryonic tissue.
• Slow-growing tumors (suprasellar region)
• Can be solid, cystic, or a combination.
  • Hypothalamus dysfunction:
  • Children (<15): Growth retardation, delayed sexual development, obesity, HA, visual symptoms, papilledema and hydrocephalus
  • Adults (50-70 year olds): Endocrine dysfunction (diabetes, amenorrhea, galactorrhea), progressive vision loss, papilledema is uncommon, VF defects, bitemporal hemianopia, incongruous homonymous hemianopia.
• Radiological features:
  • VF defect
  • Suprasellar calcification (50-70%)
  • Odontogenic cells
  • Often benign
  • Surgery is difficult
  • Radiation treatment
  • Recurrences common

Meningioma

• Middle-aged women (pregnancy stimulates growth).
• Arise from arachnoidal cap cells (multi-lobed).
• Slowly progressive; malignant or benign.
• Location:
  • Optic nerve sheath (exophthalmos, chronic disc edema, followed by atrophy, collateral vessels)
  • Tuberculum sellae (junction of chiasm and optic nerve)
  • Lateral portion of sphenoid bone
  • Olfactory groove
  • Loss of smell.
• Signs & Symptoms:
  • Asymmetric vision loss
  • Nonspecific headache
  • Proptosis, chemosis, engorgement of orbital vasculature
  • Optic disc (normal, papilledema, pallor)
  • Chiasm: asymmetrical VF defect
  • Radiologic features: hyperostosis
  • Treatment: surgery, radiation

Glioma

• Primary astrocytic tumors.
• Infiltrate optic nerve, optic tract, radiations, hypothalamus, 3rd ventricle.
• 70% of optic pathway gliomas develop symptoms by the 1st decade of life; 90% are detected by the 2nd decade.
  • Categories include
    • Grade 1 pilocytoma
    • Grade 2 astrocytoma
    • Grade 3 anaplastic astrocytoma
    • Grade 4 glioblastoma multiforme
• Glioma Children
  • Pilocytic Astrocytoma
  • Onset 4–8 years
  • Relatively benign
  • Slowly progressive
  • Ocular S/Sx include decreased visual acuity, unilateral eye proptosis, optic nerve atrophy, and visual field (VF) defects.
• Glioma Children Radiological features
  • Double-intensity tubular thickening of optic nerve, pseudo-CSF, and optic nerve kinking.
  • Optic Nerve Features include NF-1 patients, enlargement of the chiasm, infiltration of the hypothalamus.
• Glioma Adults
  • Rare and include malignant high-grade glioblastomas
  • Middle aged, male>female
  • Headache, rapid onset vision loss, retro-orbital pain.
  • Optic nerve edema/optic nerve atrophy
  • Treatment: surgery, radiation, chemotherapy.
  • Poor prognosis

Aneurysm

• Location:
  • ICA
  • OA
  • ACA
  • PCA
  • Circle of Willis
• Rare cause of chiasmal compression.
• Diagnosis involves CT scan and arteriography.