Occipital Lobe


Occipital lobe, Anton syndrome, Balint syndrome.

The occipital lobe extends from the parieto-occipital fissure on the medial surface of the brain to the lateral surface, where it merges with the parietal and temporal lobes. The calcarine sulcus divides the occipital lobe into lingula and cuneus, and it marks the boundary of the primary visual area (Brodmann area 17). The rest of the occipital lobe constitutes the visual association cortex (Brodmann areas 18 and 19). Its function is mainly concerned with visual perception and interpretation. Clinical symptoms associated with occipital lesions include visual field defects, cortical blindness, visual agnosias, achromatopsia, metamorphopsias, illusions, and hallucinations. Visual symptoms occur commonly in migraine. Occipital lobe is commonly involved in the posterior reversible encephalopathy syndrome secondary to medications or hypertension. Occipital lobe epilepsy may present with visual phenomena, as well as postictal blindness. Some of the clinical syndromes in the occipital lobe lesion include the following:

  1. 1. Anton syndrome (visual anosognosia or cortical blindness): A patient’s lack of awareness of their defect, associated with bilateral lesions.
  2. 2. Balint syndrome: Seen with bilateral occipital and parieto-occipital infarctions, consisting of optic ataxia, paralysis of gaze and disturbance of visual attention, and simultanagnosia.


Andersen R.A., Andersen K.N., Hwang E.J., Hauschild M. Optic ataxia: from Balint’s syndrome to the parietal reach region. Neuron. 2014;81(5):967–983.

Martinaud O. Visual agnosia and focal brain injury. Rev Neurol (Paris). 2017;173(7–8):451–460.

Ocular Oscillations


Ocular Oscillations, square wave jerks, macro square wave jerks, Ocular flutter, Opsoclonus, spasmus nutans, ocular bobbing, ocular dipping, nystagmus, saccadic dysmetria, ping-pong gaze, brainstem.

The following abnormal oscillatory eye movements are distinct from nystagmus because of waveform differences (e.g., no distinct slow and fast phases characteristic of nystagmus):

  1. I. Ocular bobbing consists of intermittent downward jerks of both eyes, followed by a slow drift to primary position. It is seen with destructive lesions of the pons but also occurs with pontine compression, obstructive hydrocephalus, and metabolic encephalopathy. Reflex eye movements are usually not brought out in this situation.
  2. II. Ocular dipping is an inverse movement (slow downward, fast upward) with unreliable localization.
  3. III. Ping-pong gaze denotes slow, horizontal, conjugate drift of the eyes that alternates every few seconds and is seen with bilateral hemispheric dysfunction.
  4. IV. Ocular myoclonus refers to pendular vertical oscillations seen with brainstem lesions often accompanied by rhythmic palatal movements. It typically occurs with lesions between the red nucleus, inferior olive, and dentate nucleus.

The term saccadic oscillation includes several specific entities:

  1. I. Saccadic dysmetria can produce oscillation when overshooting saccades are followed by one or more corrective saccades.
  2. II. Square wave jerks are seen most prominently in cerebellar disorders and progressive supranuclear palsy; saccades interrupt fixation with normal intersaccadic intervals.
  3. III. Macro square wave jerks are seen in multiple sclerosis and olivopontocerebellar atrophy.
  4. IV. Ocular flutter and opsoclonus produce flurries of rapid eye movements without an intersaccadic interval; movements may be purely horizontal (flutter) or multidirectional (opsoclonus). Both can be secondary to viral infection, drug effects, tumor, or paraneoplastic syndromes such as neuroblastoma in children or with anti-Purkinje cell antibodies in adults (mostly women with gynecologic tumors).

Superior oblique myokymia is a monocular torsional oscillation of small-amplitude, high-frequency contractions of a monocular superior oblique muscle. It causes oscillopsia, diplopia, or visual blurring. Although sometimes seen with brainstem disease, it is usually idiopathic and may respond to carbamazepine therapy.

Spasmus nutans is an ocular oscillation accompanied by head nodding and torticollis. It appears before 18 months of age and remits spontaneously, usually by age 3 years. The abnormal eye movements are usually dysconjugate and vary in direction. Although usually benign, this entity must not be confused with signs of intracranial tumor; the presence of poor feeding, optic atrophy, or raised intracranial pressure should be investigated by neuroimaging studies.


Biousse V., Newman N.J. Neuro-ophthalmology illustrated. ed 2 New York: Thieme Medical Publishers, Inc.; 2015.

Leigh J.R., Zee D., eds. The neurology of eye movements. ed 4 New York: Oxford University Press; 2006.



Olfaction, olfactory dysfunction, hyposmia, hyperosmia, anosmia, olfactory hallucinations

The sense of smell is mediated by the first cranial nerve. It is the only sensory modality without a thalamic relay before synapsing in the cortex. Deficits in olfaction include anosmia, hyposmia, parosmia, or loss of appreciation of flavors in food.

Smell is tested clinically using non-irritating, aromatic compounds such as oil of wintergreen, cloves, coffee, almond oil, or lemon oil. The stimulus is presented to one nostril with the other occluded. The ability to appreciate the presence of a substance, even if not properly identified, is evidence that anosmia is not present. Unilateral anosmia is more often due to a structural lesion rather than a diffuse process. More detailed olfactory testing using the University of Pennsylvania Smell Identification Test can distinguish hyposmia, anosmia, or malingering.

Causes of anosmia or hyposmia include the following:

  1. I. Infection: URI (most frequent cause of olfactory dysfunction), rhinitis, sinusitis, basilar meningitis, frontal abscess, osteomyelitis (frontal, ethmoidal), viral hepatitis, syphilis, influenza.
  2. II. Toxic or metabolic disorders: pernicious anemia, zinc deficiency, lead and calcium intoxication, diabetes mellitus, hypothyroidism, medication effects.
  3. III. Neoplasms: frontal tumor, olfactory groove or sphenoid meningioma, radiation therapy.
  4. IV. Head trauma, including trauma to cribriform plate.
  5. V. Congenital: olfactory agenesis (Kallmann syndrome) and septo-optic dysplasia (De Morsier syndrome).
  6. VI. Others: hydrocephalus, amphetamine and cocaine abuse, smoking, trigeminal lesions (causing mucosal atrophy), anterior cerebral artery disease, Sheehan syndrome, nasal polyps, multiple sclerosis, sarcoidosis, aging, Alzheimer disease, Parkinson disease (hyposmia commonly presents years before disease onset).

Anosmia most commonly occurs secondary to head trauma, and may not be noticed until several weeks or months after the injury. A third of the cases spontaneously resolve within a year.

Hyperosmia is seen in somatization disorders, migraine, hyperemesis gravidarum, cystic fibrosis, Addison disease, and strychnine poisoning. Multiple chemical sensitivity syndrome is a vague disorder associated with unexplained odor sensitivity and excitability to multiple chemical and environmental stimuli.

Olfactory hallucinations are a feature of mesial temporal lobe seizures (“uncinate fits”), which may be triggered or even arrested by olfactory stimulation. Anosmia is not present in such cases. They may also be seen in psychiatric disease (olfactory reference syndrome) and neoplasms or vascular disease involving the inferomedial temporal lobe.

There is no current effective medical treatment for most cases of olfactory loss; however, systemic steroids can be tried in post-viral, conductive, and idiopathic olfactory loss. Removal of offending agents (drugs, etc.) and treatment of underlying cause may also help improve olfaction.


Cho S.H. Clinical diagnosis and treatment of olfactory dysfunction. Hanyang Med Rev. 2014;34:107–115.

Dawes P.J. Clinical tests of olfaction. Clin Otolaryngol Allied Sci. 1998;23(6):484–490. doi:10.1046/j.1365-2273.1998.2360484.x.

Opalski Syndrome


Opalski syndrome, Babinski-Nageotte syndrome, Wallenberg syndrome.

Opalski syndrome refers to lateral medullary syndrome (Wallenberg syndrome), plus ipsilateral hemiplegia. Lesion is usually located lower than that in Wallenberg syndrome, involving the corticospinal fibers caudal to the pyramidal decussation. The syndrome is usually caused by vertebral artery occlusion. A related syndrome is Babinski-Nageotte syndrome, which manifests contralateral hemiparesis due to hemimedullary infarct before the pyramidal tract decussation.


Katsumata M., Oki K., Nakahara J., Izawa Y., Abe T., Takahashi S. Ipsilateral facial tactile hypesthesia in a patient with lateral medullary syndrome. J Stroke Cerebrovasc Dis. 2015;24(11):e315–e317.

Uemura M., Naritomi H., Uno H., et al. Ipsilateral hemiparesis in lateral medullary infarction: clinical investigation of the lesion location on magnetic resonance imaging J Neurol Sci. 2016;365:40–45.



Ophthalmoplegia, diplopia, cranial nerves, internuclear ophthalmoplegia, nystagmus, one-and-a-half syndrome

If a patient complains of diplopia or if extraocular muscle testing reveals misalignment of the visual axes, first determine whether this is due to nerve palsy or some other causes of impaired motility.

  1. I. Causes of impaired ocular motility other than nerve palsy

    1. A. Concomitant strabismus
    2. B. Graves ophthalmopathy (most commonly inferior and medial recti muscles)
    3. C. Myasthenia gravis (and other pharmacologic or toxic causes of neuromuscular blockade)
    4. D. Convergence spasm
    5. E. Blowout fracture of the orbit with entrapment myopathy
    6. F. Restrictive ophthalmopathy (Brown’s superior oblique tendon sheath syndrome)
    7. G. Orbital inflammatory disease (orbital pseudotumor)
    8. H. Orbital masses, neoplasms
    9. I. Orbital infections
    10. J. Brainstem disorders causing abnormal prenuclear inputs (internuclear ophthalmoplegia [INO], skew deviation)
    11. K. Ocular myopathies
    12. L. Chronic progressive external ophthalmoplegia (CPEO; Kearns-Sayre and related mitochondrial syndromes)
    13. M. Congenital syndromes

  2. II. Causes of abducens nerve (CN VI) palsies

    1. A. Nuclear (associated with ipsilateral horizontal gaze palsy)

      1. 1. Developmental anomalies (Möbius, Duane syndromes)
      2. 2. Infarction
      3. 3. Tumor (pontine glioma, cerebellar tumors)
      4. 4. Wernicke-Korsakoff syndrome

    2. B. Fascicular

      1. 1. Infarction
      2. 2. Demyelination
      3. 3. Tumor

    3. C. Subarachnoid space lesions

      1. 1. Aneurysm or anomalous vessels (anterior inferior cerebellar artery, basilar artery)
      2. 2. Subarachnoid hemorrhage
      3. 3. Meningitis (infectious, neoplastic)
      4. 4. Sarcoidosis
      5. 5. Cerebellopontine angle tumor (acoustic neuroma, meningioma)
      6. 6. Clivus tumor (chordoma, nasopharyngeal carcinoma)
      7. 7. Trauma
      8. 8. Surgical complication
      9. 9. Postinfectious

    4. D. Petrous

      1. 1. Infection or inflammation of mastoid or petrous tip
      2. 2. Trauma (petrous fracture)
      3. 3. Thrombosis of inferior petrosal sinus
      4. 4. Increased intracranial pressure (idiopathic intracranial hypertension, supratentorial mass)
      5. 5. Following lumbar puncture
      6. 6. Aneurysm
      7. 7. Persistent trigeminal artery
      8. 8. Trigeminal schwannoma

    5. E. Cavernous sinus and superior orbital fissure

      1. 1. Aneurysm
      2. 2. Cavernous sinus thrombosis
      3. 3. Carotid cavernous fistula
      4. 4. Dural arteriovenous malformation
      5. 5. Tumor (pituitary adenoma, meningioma, nasopharyngeal carcinoma, metastasis)
      6. 6. Pituitary apoplexy
      7. 7. Sphenoid sinusitis (mucormycosis)
      8. 8. Herpes zoster
      9. 9. Granulomatous inflammation (sarcoidosis, Tolosa-Hunt syndrome)

    6. F. Orbital

      1. 1. Tumor
      2. 2. Infection
      3. 3. Trauma

    7. G. Uncertain localization

      1. 1. Nerve infarction (diabetes, hypertension, arteritis)
      2. 2. Migraine

  3. III. Causes of trochlear nerve (CN IV) palsies

    1. A. Nuclear and fascicular

      1. 1. Developmental anomalies
      2. 2. Hemorrhage
      3. 3. Infarction
      4. 4. Trauma
      5. 5. Demyelination
      6. 6. Surgical complications

    2. B. Subarachnoid

      1. 1. Trauma
      2. 2. Tumor (pineal, tentorial meningioma, trochlear schwannoma, ependymoma, metastases)
      3. 3. Surgical complication
      4. 4. Meningitis (infectious, neoplastic)
      5. 5. Mastoiditis

    3. C. Cavernous sinus and superior orbital fissure

      1. 1. As for CN VI palsies

    4. D. Orbital

      1. 1. Trauma
      2. 2. Ethmoiditis
      3. 3. Ethmoidectomy

    5. E. Uncertain localization

      1. 1. Infarction (diabetes, hypertension, arteritis)

  4. IV. Causes of oculomotor nerve (CN III) palsies

    1. A. Nuclear and fascicular

      1. 1. Developmental anomaly
      2. 2. Infarction
      3. 3. Tumor

    2. B. Subarachnoid

      1. 1. Aneurysm (posterior communicating artery)
      2. 2. Meningitis (infectious, syphilitic, neoplastic)
      3. 3. Infarction
      4. 4. Tumor
      5. 5. Surgical complication

    3. C. Tentorial edge

      1. 1. Increased intracranial pressure (uncal herniation, idiopathic intracranial hypertension)
      2. 2. Trauma

    4. D. Cavernous sinus and superior orbital fissure

      1. 1. As for CN IV and VI palsies
      2. 2. Infarction

    5. E. Orbital

      1. 1. Trauma
      2. 2. Tumor
      3. 3. Infection

    6. F. Uncertain localization

      1. 1. Mononucleosis and other viral infections
      2. 2. Following immunization
      3. 3. Migraine
      4. 4. Cyclic oculomotor palsy of childhood
      5. 5. Guillain-Barré and Miller-Fisher syndromes
      6. 6. Sjögren and Behçet syndromes

Combined ophthalmoparesis (third, fourth, and sixth cranial nerve involvement) most commonly occurs with base of skull infiltrations, cavernous sinus or superior orbital fissure lesions, and generalized neuropathies. Proptosis, chemosis, and vascular engorgement suggest orbital or cavernous sinus involvement. Base of skull problems include extension of nasopharyngeal carcinoma, sarcoidosis, lymphoma, clivus chordoma, pituitary apoplexy, meningeal carcinoma, and cavernous sinus thrombosis.

CPEO is a slowly progressive, painless, symmetrical ophthalmoplegia, without fluctuations or remissions. Saccades are slow, usually with no diplopia. Ptosis and orbicularis oculi weakness usually accompany the external ophthalmoplegia. The pupils are spared, and there are no orbital signs. Fibrotic changes of the extraocular muscles may occur over time, causing a superimposed restrictive ophthalmopathy. CPEO has multiple causes. Mitochondrial cytopathy (Kearns-Sayre syndrome) is one cause. Painful ophthalmoplegias may be due to diabetes, aneurysm, tumors (primary and metastatic), Tolosa-Hunt syndrome (granulomatous inflammatory process affecting the cavernous sinus and surrounding structures), herpes zoster, cavernous sinus thrombosis, carotid cavernous fistula, ophthalmoplegic migraine, arteritis, carcinomatous meningitis, or fungal infection.

INO is characterized by (1) slow, incomplete adduction of the eye or complete inability to adduct past midline (convergence movements may be preserved) and (2) dissociated nystagmus of the opposite abducting eye. Skew deviation (hypertropia on the lesion site) is often present. INO is caused by a lesion of the medial longitudinal fasciculus (MLF) between mid-pons and the oculomotor nucleus ipsilateral to the side of impaired adduction. Subtle defects are best solicited by observing the fast phases of optokinetic nystagmus. In bilateral INOs, gaze-evoked vertical nystagmus, impaired vertical pursuit, and decreased vertical vestibular responses are often present. The most frequent cause of INO in young adults (especially when bilateral) is multiple sclerosis. Vascular causes are more common in older patients. Other causes include intra- or extra-axial brainstem tumors, hydrocephalus, subdural hematoma, infection, nutritional and metabolic disorders, and drug intoxication. Myasthenia gravis and Miller-Fisher syndrome could cause similar appearing “pseudo-INO.”

One-and-a-half syndrome refers to ipsilateral horizontal gaze palsy and INO (see Gaze palsy). This results from combined lesions of the MLF and the more ventral, ipsilateral abducens nucleus or paramedian pontine reticular formation (PPRF). The only intact horizontal movement is abduction of the contralateral eye. Acutely, the patient may appear exotropic, with nystagmus in the deviated eye. Vergence and vertical movements may be spared. Causes include brainstem ischemia (most common), multiple sclerosis, tumor, or hemorrhage. As with INO, myasthenia must be considered if there are no long tract or sensory signs. There is also a vertical one-and-a-half syndrome due to a dorsal midbrain lesion.

Aug 12, 2020 | Posted by in NEUROLOGY | Comments Off on O
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