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Ring lesions on MRI of the brain raise suspicion of abscess or renal cell carcinoma, but seldom both.
A man of 57 was found unresponsive after three weeks of weight loss, cough with haemoptysis and diplopia. His only noteworthy medical history was ankylosing spondylitis. He was profoundly confused, pyrexial (39.1 °C), cachectic, apathetic and doubly incontinent. On examination he was tachypnoeic and at the right lung base there was percussion dullness, reduced air entry and bronchial breathing; there was weakness in the upper and lower limbs (4/5), most pronounced at the right shoulder (3/5); vertical nystagmus and a pout reflex were present. He had a neutrophilia of 28 × 109/L. A chest X-ray demonstrated right lower zone consolidation with a cavitating lesion. MRI of the brain showed 20 rounded lesions with enhancing rims in both hemispheres; the largest, located in the left parietal lobe, measured 2 cm in diameter (Figure (Figure1a1a,,1b). 1b). An extracerebral collection was present over the right parietal lobe. A chest/abdomen CT scan showed a moderate left pleural effusion with minor consolidation and a small right pleural effusion with cystic areas containing air—fluid levels. A soft tissue mass was present in the right kidney.
Renal cell carcinoma with cerebral metastases was suspected radiologically, because of the lack of vasogenic oedema surrounding the lesions. However, diagnostic pleural aspiration yielded 30 mL of pus. Bilateral pleural empyemas were aspirated under ultrasound guidance. Multiple brain abscesses were then suspected: the patient was started on intravenous ceftriaxone and metronidazole and transferred for neurosurgery. Stereotactic drainage of pus from the right subdural space confirmed a subdural empyema. The pus contained Gram-positive cocci. On simultaneous stereotactic biopsy, the largest ring-enhancing lesion was confirmed histologically as a brain abscess. Back in our department, ultrasound-guided aspiration of the right renal mass yielded 120 mL of pus; a pigtail catheter was inserted and drained a further 150 mL. Streptococcus anginosus was cultured from pleural and perinephric aspirates; cytology showed no malignant cells; multiple blood cultures were negative. Echocardiography and HIV and Mantoux tests were normal.
The patient's condition improved with antibiotic therapy. After the perinephric catheter ceased draining, a repeat abdominal CT scan showed a persistent perinephric abnormality. CT-guided aspiration was performed to reposition a drainage catheter. Unexpectedly, only solid tissue was found, and biopsy revealed papillary renal cell carcinoma. The patient underwent an uncomplicated right radical nephrectomy. The tumour measured 8.0 cm, and no capsular or vascular invasion was apparent. A follow-up MRI brain scan at two months showed almost complete regression of all lesions. The patient subsequently recovered fully.
Ring-enhancing brain lesions are difficult to diagnose from the images alone since brain abscesses can mimic cerebral neoplasia and vice versa1. Multiple brain abscesses are rare. Most reports are isolated cases, the largest series being of only sixteen patients over 16 years2. To our knowledge there are no reports of multiple brain abscesses in association with malignancy. The multiple intracerebral lesions in our patient—initially thought to have renal malignancy and then found to have empyemas—presented a particular diagnostic dilemma. Currently, aspiration or more aggressive surgical drainage of brain abscesses over 2.5 cm in diameter is recommended1,2, and only the largest was drained. Had other lesions not responded to antibiotics, drainage as well as diagnostic biopsy for malignancy would have been necessary. Serial MRI brain scanning played a principal role in monitoring abscess regression during antibiotic therapy. The near complete regression of all intracerebral lesions on serial MRI scanning, and the continued clinical improvement, indicated that none of the cerebral lesions was a metastasis.
Without the follow-up abdominal CT scan after drainage of the perinephric abscess, the renal tumour might not have been detected. A report of four patients with pyogenic renal infections and kidney tumours suggested that the tumour might predispose to renal abscess formation3. We are not aware of any reports of S. anginosus causing a perinephric abscess, but this nomenclature is relatively new; S. anginosus is the preferred name for one of the organisms that used to be called the ‘milleri streptococci’ or S. milleri, and these organisms are known to cause brain abscesses, pleural empyema and abdominal infections4. The infections are usually local, involving one single viscus or mucous membrane, though possibly at multiple sites4. It is especially unusual for a patient to have so many different and widely disseminated sites of infection simultaneously. In a report of fifty-one cases of S. milleri group bacteraemia, which included a review of a further 158 cases from previous publications, one localized area of infection was the rule5. It is noteworthy that eight of these patients had underlying neoplasia.