4

Acute Homonymous Hemianopsia

in Febrile Patient

CASE NO. 4

A 22-year-old white female presented in the ER complaining of high fever and chills after undergoing a piercing in her nose (Fig. 4.1). She also related some difficulty with her vision on her left side. Past medical history was unremarkable. On examination her visual acuity was 20/20 in each eye. Ocular motility was full in both eyes. Pupillary examination was normal. The Goldmann visual field showed an inferior left homonymous hemianopia (Fig. 4.2). Slit lamp examination was unremarkable. Ophthalmoscopy was within normal limits.

Discussion

Dr. Brazis. An inferior homonymous quadrantanopia is most often due to a superior occipital lesion or a parietal lesion. In patients with occipital lesions, the field defects often occur in isolation, while other localizing signs or parietal involvement are usually evident in patients with parietal lesions. Therefore, although visual field defects may occur in relative isolation with parietal lobe lesions, lesions in this location more often betray themselves by other signs of neurologic dysfunction. Parietal lobe lesions may be associated with contralateral somatosensory impairment, including impaired object recognition, impaired position sense, impaired touch and pain sensation, and tactile extinction. Dominant parietal

43

Emergencies in Neuro-Ophthalmology: A Case Based Approach

Fig. 4.1. External photography showing the nose piercing.

Fig. 4.2. Goldman visual field showing the inferior right homonymous hemianopia.

lesions may cause apraxia, finger agnosia, acalculia, right-left disorientation, alexia, and aphasic disturbances. Non-dominant lesions may be associated with a anosognosia (denial of neurologic impairment), autotopagnosia (failure to recognize himiplegic limbs as belonging to the self), spatial disorientation, hemispatial neglect, constructional apraxia (abnormal drawing and copying), and dressing apaxia.

In a patient with fever and chills and a visual field defect, one must be concerned about the possibility of an infectious process

44

Acute Homonymous Hemianopsia in Febrile Patient

affecting the central nervous system. Lesions producing such impairment include abscesses, aneurysms, empyema, encephalitis, granuloma, meningitis, and ischemic infarction related to endocarditis or sepsis.

An abscess is a circumscribed area of pus that may be epidural, subdural, or intracerebral. Intracerebral abscesses are usually solitary and are most often located in the cerebral hemispheres. Most intracranial abscesses are caused either by local invasion of one or more organisms or by septic emboli. An untreated or incompletely treated middle ear infection is the most common source of a locally derived brain abscess. Chronic mastoiditis may produce brain abscess as may chronic paranasal sinusitis. Orbital cellulitis may cause intracranial abscess but these are usually frontal or temporal in location caused by extension of the organism through the superior orbital fissure. Acute bacterial meningitis is a rare cause of brain abscess except in neonates. Septic foci on the scalp or face are relatively rare cause of brain abscess. Dental infections, tonsillitis, or other facial infections may cause an abscess. Cerebral abscesses may also occur after trauma or neurosurgical procedures. Metastatic abscess seas that result from blood-borne organisms may develop in the setting of bacteremia or septicemia. Such abscesses are usually multiple and may be of varying size.

Most intracranial abscesses are caused by bacteria. Aerobic bacteria are found more often than anaerobic bacteria, but polymicrobial infections may exist in a single abscess. The most common aerobic bacteria that produce both single and multiple intracranial abscess are Gram-positive cocci, such as Streptococcus and Staphlococcus species, and Gram-negative bacilli, including Haemophilus species and many members of the Enterobacteriaceae. Nevertheless, Gram-negative cocci, such as Neisseria meningitides, and Gram-positive bacilli, such as Listeria monocytogenes, Actinomycosis, and Nocardia, can produce brain abscess in otherwise healthy people. The most common anaerobic bacteria that cause brain abscesses are the Gram-negative bacilli, Bacteroides and Propionibacterium. Organisms other than bacteria may produce

45

Emergencies in Neuro-Ophthalmology: A Case Based Approach

intracranial abscesses, particularly in chronically ill, immunodeficient, or immunosuppressive patients. These include fungi, toxoplasmosis, Cysticercus species, Angiostrongylus cantonensis, and Treponema pallidum.

Neuroimaging, preferably contrast MRI studies, are warranted urgently. Suppurative encephalitis appears as an area of decreased density on a CT scan, whereas an abscess appears as a low-density core surrounded by a capsule that enhances when the patient is given an intravenous injection of iodinated contrast agent. Features of abscess on MRI study include:

•Peripheral edema producing mild hypointensity on T1-weighted images and marked hyperintensity on proton density-weighted and T2-weighted images;

•Central necrosis with abscess fluid that is hypointense relative to white matter and hyperintense relative to CSF on T1-weighted images and hyperintense relative to gray matter on proton densityweighted and T2-weighted images;

•Extraparenchymal spread (intraventricular or subarachnoid) manifested by increased intensity relative to normal CSF on T1-weighted images, proton density-weighted, and T2 weighted images;

•Visualization of the abscess capsule is isoor mildly hyperintense relative to brain on T1-weighted image and isoto hypointense related to white matter on proton density-weighted and T2weighted images.

Course. Initial acute brain CT with contrast in our patient demonstrated a ring enhancing lesion in the left occiptal lobe consistent with brain abscess (Fig. 4.3). Diffusion-weighted image (DWI) MRI of the brain demonstrates high signal in the left occipital region corresponding to the area of ring enhancement, representing pus within the abscess (Fig. 4.4). It is thought that the abscess was due to infection from the patient’s recent nose piercing.

Dr. Brazis. The treatment of an intracranial abscess is directed both at the abscess and its source, and may be medical, surgical, or both.

46

Acute Homonymous Hemianopsia in Febrile Patient

Fig. 4.3. Brain CT with contrast demonstrates the ring lesion in the left occiptal lobe (arrow) consistent with brain abscess.

Fig. 4.4. Diffusion-weighted image of the brain demonstrates high signal in the left occipital region (arrow) corresponding to the area of ring enhancement on the previous image representing an abscess.

47

Emergencies in Neuro-Ophthalmology: A Case Based Approach

Medical treatments usually consist of appropriate antibiotics or other drugs designed to eliminate the organism causing the infection. The blood brain barrier is altered in areas of cerebritis and abscess, thus allowing increased penetration of anti-infectious agents. Occasionally, corticosteroids are used to reduce the cerebral edema surrounding the intracranial abscess. The specific medical regimen recommended depends on the known or presumed causative organism. In patients with no significant neurologic deficits with a normal state of consciousness, with a single deep abscess less than 2 cm in diameter, harboring multiple abscesses, or for whom surgery of any type might be inappropriately hazardous, medical treatment alone may be successful in eradicating the abscess. If there is clinical deterioration, if CT scanning or MR imaging reveals enlargement of the abscess at any time during medical treatment, or if there is no decrease in size of the abscess within several weeks, surgery should be considered. Most patients with an intracerebral abscess should undergo aspiration or excision of the abscess for both diagnosis and treatment. Aspiration is usually all that is required. When a brain abscess results from a systemic infection, the source of infection also must be treated (e.g. bacterial endocarditis).

Dr. Lee. An intracerebral abscess can be a life-threatening condition. Although the classic triad of fever, headache and focal neurologic deficit (e.g. homonymous hemianopsia) are useful findings, these findings do not always occur in patients with a brain abscess. Likewise, an elevated white blood cell count or elevated erythrocyte sedimentation rate is only variably present if at all. Classically, a ring-enhancing mass lesion on CT or contrast MRI could be an abscess, a primary brain tumor or a metastasis. DWI in a brain abscess might show hyperintense signal as opposed to the other lesions in the differential, which normally would not be bright on DWI. A patient thought to have a primary brain tumor might undergo a biopsy alone and be discharged pending the pathology if an abscess is not considered ahead of time in the differential diagnosis. The absence of fever,

48