Case of the Week

Background:

• Being rare clinical entities, the development of fungal abscesses is dependent on the patient’s immune system and fungal virulence factors. The major contributing factors for decreased host immunity are increasing incidence of organ transplants, chemotherapies, and HIV infections. Common routes of spread of infection are hematogeneous dissemination from a distant focus such as lung, through direct implantation after trauma, or secondary to the local extension from sinonasal, orbital, or spinal infections. An aggressive diagnostic approach and timely initiation of antifungal therapy is imperative to reduce morbidity and mortality.
• The most common fungi are Cryptococcus and Candida. Due to their small size, they can access the microcirculation and can cause diffuse leptomeningitis or manifest as parenchymal granulomas or abscesses. Aspergillus and Mucor due to their larger size cannot access the meningeal microcirculation and cause a more focal disease. They cause cerebritis, abscess formation, or involvement of larger vessels resulting in vasculitis, vascular occlusion, cerebral infarctions, or formation of mycotic aneurysms.
• In our case, the patient had fungal sinusitis of the right maxillary sinus that was proven after debridement. This was a case of fungal abscess due local extension from sinonasal disease.

Clinical Presentation:

• Nonspecific symptoms like weight loss, fever, malaise, and fatigue are common symptoms. CNS involvement is characterized by headache, meningismus, change in mental status, and seizure. 

Key Diagnostic Features:

• On T1WI, fungal abscesses demonstrate a hypointense core with a surrounding iso- to mildly hyperintense rim. T2WI shows increased signal intensity of the core of the lesion with a surrounding rim of hypointensity. Peripheral enhancement is seen on T1-weighted postcontrast sequence.
• Fungal abscesses may contain lipids (1.2–1.3 ppm), lactate (1.3 ppm), alanine (1.5 ppm), acetate (1.9 ppm), succinate (2.4 ppm), and choline (3.2 ppm) that can be visualized on MR spectroscopy. A typical feature of fungal infections is the disaccharide trehalose (3.6 ppm) as a distinctive component of the fungal wall.

Differential Diagnoses:

• Pyogenic, tubercular, and carcinomatous meningiti:
  • Pyogenic abscess usually shows T1 hypointense wall in contrast to hyperintense wall of fungal abscess. Blooming on SWI in the abscess wall is also seen due to mineral fungal components. This helps differentiate fungal from pyogenic abscess. On spectroscopy, pyogenic abscesses show lactate peak at 1.3 ppm and amino acid peak at 0.9 ppm.
  • Tubercular abscesses show prominent lipid peak. Associated features like basal exudates and tuberculomas may also be seen.
  • Carcinomatous meningitis shows diffuse leptomeningeal thickening and enhancement along with ring-enhancing lesions.
• Other mimics of fungal abscesses are primary neoplasms such as glioblastoma with central necrosis and metastasis. Perfusion is raised in enhancing areas of glioblastoma. Metastases show low NAA peak.

Treatment:

• The goals of treatment are: 1) relief of mass effect when present, 2) identification of a pathologic agent by specimen culture, 3) control and eradication of infection, 4) minimization of loss of neurologic function, and 5) systemic supportive care.
• Antifungal agents in general have poor penetration across the blood-brain barrier, and medical therapy alone is not indicated for fungal brain abscesses. Antifungal agents are selected based upon the offending agent.
• Candida albicans infection is treated with amphotericin B, fluconazole, or caspofungin. Cryptococcal infections require amphotericin B and flucytosine, though fluconazole can be used as an alternative. Liposomal amphotericin B has increased permeability across the blood-brain barrier and has been used to treat Aspergillus nonsurgically; however, A. fumigatus and Mucormycosis species abscesses are still best treated with surgery followed by antifungal therapy. Prophylaxis with anticonvulsants is recommended for all patients with brain abscesses.