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Note on ocular signs of parietal lobe tumour

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parietal lobe tumors AND visual field defects

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parietal lobe lesion visual field defect inferior quadrantanopia neglect neuro-ophthalmology

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Ocular signs of a parietal lobe tumour

A parietal tumour affects the superior optic radiations, which carry information from the inferior visual fields. Ocular findings are therefore usually contralateral and homonymous.

Localizing visual signs

  1. Contralateral homonymous inferior quadrantanopia
    • The classic defect is a loss of the lower quadrant of the visual field on the side opposite the lesion:
      • Left parietal tumour → right inferior homonymous quadrantanopia.
      • Right parietal tumour → left inferior homonymous quadrantanopia.
    • Known as “pie on the floor”.
    • It results from involvement of superior parietal optic-radiation fibers. Visual-pathway review describes parietal lesions as tending to cause inferior field defects.
  2. Contralateral homonymous hemianopia
    • A larger or deeper lesion involving the main optic radiations can cause a complete or nearly complete homonymous hemianopia.
    • The defect is often relatively congruous, meaning the visual-field loss is similar in both eyes.
  3. No primary ocular abnormality
    • Visual acuity is usually preserved.
    • Pupillary light reflexes are usually normal, with no relative afferent pupillary defect, because the lesion is posterior to the lateral geniculate body.
    • Fundus may initially be normal.
  4. Optokinetic nystagmus abnormality
    • Smooth pursuit and the slow phase of optokinetic nystagmus may be defective when the target moves towards the side of the parietal lesion.
    • Thus, in an isolated homonymous hemianopia, asymmetric optokinetic responses can support a parietal, rather than occipital, localization.

Associated higher visual signs

  • Visual neglect, especially with a right parietal tumour: neglect of the left side of space, sometimes mistaken for a left homonymous hemianopia.
  • Impaired visuospatial orientation, constructional apraxia, and difficulty dressing may occur with a nondominant parietal lesion.
  • A dominant, usually left, parietal lesion may cause Gerstmann syndrome: agraphia, acalculia, finger agnosia, and right-left disorientation.

Signs due to raised intracranial pressure

These are not specific to a parietal location but may occur with a large tumour:
  • Bilateral papilledema
  • Transient visual obscurations
  • Diplopia from a sixth-nerve palsy
  • Late optic atrophy with visual loss
Key examination answer: A parietal lobe tumour typically produces a contralateral inferior homonymous quadrantanopia (“pie on the floor”), or a contralateral homonymous hemianopia if the lesion is extensive, often with visual neglect and no early pupillary or fundus abnormality.
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