Pyogenic brain abscess associated with an incidental pulmonary arteriovenous malformation

Background

A pulmonary arteriovenous malformation (PAVM) is an aberrant communication between the arterial and venous supply of the pulmonary vasculature, bypassing the normal capillary bed between them.1 PAVMs can present with or without symptoms and can exist as solitary, multiple or part of a syndrome such as the genetic condition hereditary haemorrhagic telangiectasia (HHT).

Streptococcus intermedius is a bacterium commonly found in the normal microbiome of the gastrointestinal, respiratory and genitourinary tracts; however, it has been also recognised as one of the most common pathogens in abscesses of the central nervous system.2 Dental infections or cleanings can be a source of initial infection with subsequent seeding into the brain.

We report a case of a S. intermedius brain abscess, dental infection and an incidentally discovered asymptomatic PAVM that potentially linked the odontogenic infection to cerebral abscess formation.

Case presentation

A woman in her late 80s presented to the emergency department with a new and progressively worsening right-sided headache. The headache began 1 week prior to presentation and was described as a throbbing pain. The headache was associated with global weakness, fatigue, gait imbalance and behaviour changes. Friends and family noted she was less interactive, and her speech was slowed. She had no relevant medical history. At baseline, she lived alone, was independent in all instrumental and basic activities of daily living, and regularly engaged in activities in the community, including music lessons. She had no recent trauma or falls. She had no associated vision or hearing changes, numbness or weakness of her extremities, nausea, vomiting or urinary incontinence.

On presentation, she was afebrile with a blood pressure of 134/77 mm Hg, a pulse of 52 beats per minute and an oxygen saturation of 96% on room air. On physical examination, she was alert and fully oriented with a normal cardiopulmonary examination. Neurological examination was notable for 4+/5 weakness of the left upper and lower extremities, left hemianopsia and a wide-based, unsteady gait. Sensory, reflex, cranial nerve and cerebellar examinations were normal. There were no mucosal or skin telangiectasias.

Investigations

Initial laboratory data included a normal white cell count of 8.2 x10^∧9/Lwith 75% neutrophils. The patient’s haemoglobin, comprehensive metabolic panel, and urinalysis were within normal limits and an HIV test was negative. Chest radiograph was normal (figure 1). CT of the head demonstrated two hypodense masses in the right temporal lobe measuring 2.5×3.4 cm and 1.5×1.5 cm with surrounding vasogenic oedema, effacement of the right lateral ventricle and 5 mm of leftward midline shift. MRI of the brain was ordered. The neurosurgery service was consulted and recommended a CT of the chest, abdomen and pelvis to evaluate for an underlying malignancy, with a working diagnosis of a brain metastasis. This imaging study showed a right lower lobe PAVM and a uterine mass consistent with, but not diagnostic of, a fibroid (figure 2).

Differential diagnosis

Considering the CT findings, metastatic malignancy was initially of highest concern due to the patient’s advanced age and the presence of an uncertain pelvic mass. A primary malignancy of the central nervous system was less likely epidemiologically. The diagnosis of brain metastases from a presumed gynaecological origin was shared with the patient and her son, and she was admitted to the geriatrics service where her outpatient primary care provider (PCP) would be the attending physician. The leading diagnosis was rapidly abandoned when shortly following admission, MRI of the brain showed a 4.8 cm right temporal lobe lesion with irregular margination, peripheral enhancement with marked homogeneous central diffusion restriction, a ‘dual rim sign,’ and surrounding vasogenic oedema—a constellation of findings indicative of a brain abscess (figures 3 and 4).

Treatment

On establishing the diagnosis of a cerebral abscess, the neurosurgery team updated the patient and her son of this new diagnosis and explained the need for emergent surgical evacuation. The patient and her son were initially hesitant to proceed but agreed after a discussion with her PCP that reinforced the diagnosis and the risks of delaying intervention. The patient was retriaged to the neurosurgical service and underwent emergent craniotomy and abscess evacuation. Culture of the abscess yielded S. intermedius and Fusobacterium nucleatum, both common oral bacteria. Multiple sets of blood cultures remained negative and a transthoracic echocardiogram was without evidence of endocarditis. She received empiric broad-spectrum antibiotics that were narrowed to ceftriaxone and metronidazole. Because of the presence of oral flora in the abscess, a full dental examination was completed. There was mobility of the right upper second premolar. Maxillofacial CT demonstrated lucencies and mucosal thickening of the adjacent maxillary sinus concerning for infection. There was no radiographic evidence of direct communication between the tooth or maxillary sinus and brain abscess. This tooth was extracted on postoperative day three. The pulmonology service was consulted due to concern that the PAVM may have facilitated abscess formation; they recommended embolisation of the PAVM after completion of the antibiotic course.

Outcome and follow-up

She recovered well from surgery and was discharged to acute rehabilitation on hospital day 9. After a short acute rehabilitation stay, she was discharged home. She attended outpatient infectious disease and neurosurgery follow-up appointments and completed a 10-week course of intravenous antibiotics. Subsequent imaging demonstrated resolution of the abscess. The patient’s PCP remained involved in the case throughout inpatient admission, rehabilitation, and outpatient treatment and ensured follow-up with the pulmonology, infectious disease and interventional radiology subspecialists. The postoperative course was complicated by a deep vein thrombosis for which the patient was started on anticoagulation, which delayed PAVM embolisation. Approximately 6 months after her initial hospitalisation, she underwent successful coil embolisation of the PAVM by the interventional radiology team (figures 5 and 6). She has done well, experiencing resolution of her headaches, weakness and personality changes. She has been able to resume all of her prior activities.