Giant anterior interhemispheric fissure amoebic abscess: A rare case
Entamoeba histolytica, a protozoan, is the causative agent of amoebiasis. Nearly 10% of the world's population is infected with E. histolytica, which includes India and nations in the tropical regions of Africa, South and Central America, and Asia, due to poor sanitation and crowding., Infection is caused by ingestion of cysts contained in food or water contaminated with feces, or rarely, through the oral–anal sexual contact. Ingested cysts survive the acidity of the stomach. Trophozoites can invade the intestinal mucosa, causing amoebic colitis. They can travel through the mucosa into the bloodstream, and through the portal circulation reach the liver, causing amoebic liver abscess, which in some cases may rupture into the lung forming a hepatobronchial fistula. It can cause cerebral involvement in the form of a brain abscess in less than 0.1% cases of liver abscess. The other amoebae that can infect the brain are Acanthamoeba, Balamuthia, Sappinia, and Naegleria, which can cause granulomatous amoebic encephalitis mostly in immunocompromised people., The aim of this study is to present the first case of anterior interhemispheric fissure amoebic brain abscess.
A 22-year old boy presented to our emergency department with complaints of acute-onset altered sensorium for the last 2 days. He also had intermittent high-grade fever for the past 4 months. There were no complaints of headache, nausea, vomiting, and seizures. The patient was a known smoker and a marijuana addict.
On examination, he was conscious but disoriented, dysphasic agitated, pale, and incontinent. Decreased breath sounds in the right lower zone, neck rigidity, and Kernig's sign were present. Power in the right lower limb was 2/5 and in the left lower limb was 3/5 (Medical Research Council grading). The total leucocyte count was 20,100/mm 3 (with the eosinophil count being 0.2%). Viral markers for human immunodeficiency virus (HIV), hepatitis B, and hepatitis C were negative.
Contrast-enhanced computed tomography (CT) of the head [Figure 1]a showed a homogenous hypointense lesion with ring enhancement in the anterior interhemispheric fissure. There was massive perilesional edema with mass effect. Magnetic resonance imaging (MRI) of the brain [Figure 2] revealed a lesion in the anterior interhemispheric fissure, which was hypointense on T1-weighted images (WI), hyperintense on T2WI, and showed restriction of diffusion on diffusion-weighted imaging sequence. There was peripheral rim enhancement of the lesion after gadolinium administration [Figure 2]. There were lipid and lactate peaks on MR spectroscopy. The differential diagnosis included a bacterial brain abscess, an amoebic brain abscess and a high grade glioma.
The patient was taken up for urgent surgical evacuation of the brain abscess. A bifrontal craniotomy was performed. Intraoperatively, there was anchovy-sauce-colored pus in the abscess cavity with a thick fibrotic wall extending up to the third ventricle. Both the anterior cerebral arteries (ACAs) were seen passing through the abscess wall, which was densely adherent to the vessels. The abscess wall was excised except for the part adherent to the ACAs.
Postoperative CT scan of the head [Figure 1]b showed complete excision of the abscess. Pus microscopy was negative for any parasite. Pus cultures were sterile for bacterial, fungal, and tuberculous pathology.
Histology [Figure 3]b and [Figure 3]c showed an organized abscess consisting of foamy macrophages, gliosis and inflammatory cell infiltrates comprising of polymorphs and lymphocytes. No organisms were seen.
E. histolytica serology [immunoglobulin (Ig) G Ab enzyme-linked immunosorbent assay (ELISA)] was positive. Abdomen contrast-enhanced CT [Figure 3]a showed a 5 × 6 cm mass in segments 7 and 8 of the liver. Antibiotics including metronidazole were started on day 1. Pigtail drain was inserted in the liver which drained copious amounts of anchovy sauce-like pus from the liver abscess.
The clinical condition of the patient improved to E4V5M6 within the next 2 days, and power in both the lower limbs improved to 4/5 over 1 week. The liver abscess showed resolution on serial ultrasound imaging, the abdominal symptoms improved, and the hepatic drain was eventually removed. He was discharged on day 35. The hospital stay was prolonged due to slow resolution of the liver abscess and also due to the chest infection that developed during the hospital stay. The patient was doing well 3 months following surgery with normal power in both lower limbs.
E. histolytica is the only member of the Entamoeba genus known to cause brain abscess. Approximately half of the amoebic brain abscesses are associated with intestinal symptoms. Orbison et al., collected 64 cases of amoebic brain abscess from the literature and reported five more cases. Tamer et al., recently reported a case of multilocus amoebic brain abscess.
Headache and sensorium alteration are the most common initial presentations of cerebral amoebiasis.,, Symptoms and signs of meningitis can occur as well. Cranial nerve involvement is frequently reported.,,
Lesions within the brain have been reported as a single or confluent abscesses ,, as well as multiple abscesses.,, The right hemisphere is more likely to be involved, particularly the posterior-parietal area, occipital lobe, and parieto-occipital lobe. Two cases are reported in the posterior fossa. In our case, a large abscess was present in the anterior interhemispheric fissure with a large bifrontal extension.
The pathogenesis of an abscess, particularly in this location, could be explained by the fact that septicemia occurs due to a compromised liver function and the amoebae reach the pia-arachnoid of the interhemispheric fissure via meningeal vessels causing thrombosis and meningitis. Then, via diapedesis, they invade the brain parenchyma and cause vast necrosis and tissue death that can lead to a large interhemispheric abscess with bifrontal extension.
Serological investigation and clinical response to anti-amoebic drugs help in confirming the diagnosis of amoebic brain abscess, apart from the radiological imaging., The ELISA test with values ranging from 1:1000 to 1:50000 (dilution) are suggestive of extraintestinal amoebiasis. Serum antibodies reflect amoebic invasion but do not correlate with protective immunity. Hence, a positive amoebic serology indicates extraintestinal amoebiasis and helps in corroborating the diagnosis.,
Metronidazole is the drug of choice for treating amoebiasis of any organ. In some studies,, it was administered for 2 weeks, and in another  it was given for 8 weeks. However, the endpoint of antibiotic cessation was the resolution of the abscess. Indications for surgery include a large, multiloculated abscess, no improvement with drugs, mass effect,, poor Glasgow Coma Scale (GCS), and development of new abscesses. Surgery can be just pus drainage or it may include total excision of the abscess wall. Abscess wall, which can be excised safely, should be excised. Metronidazole is administered intravenously along with concomitant abscess drainage for the treatment of a large multiloculated amoebic brain abscess.,,,,
To the best of our knowledge, there are no recommendations in the literature regarding the total duration of antibiotics to be given or when to stop the antibiotics. In our case, the total duration of metronidazole therapy was 8 weeks, which comprised 6 weeks of intravenous and 2 weeks of oral therapy. Resolution of all the abscesses existing in the body along with improvement of the neurological status with symptomatic relief, are the indications for stopping the treatment.
The total leucocyte count in our case normalized within a week of the cranial surgery even when the liver abscess (although resolving) was still present. Hence, we cannot adequately rely on the leucocyte count for stoppage of therapy.
In our case, the histopathology of the intracranial abscess wall did not show trophozoites with engulfed red blood cells; however, the positive amoebic serology and response to anti-amoebic drugs support the diagnosis of amoebic brain abscess. Surgical evacuation is important for a rapid recovery and better response to anti-amoebic drugs.
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[Figure 1], [Figure 2], [Figure 3]