lunedì 3 dicembre 2007
Multiple fungal abscesses secondary to blastomycosis dermatitidis
Figure 1 and Figure 2: Noncontrast axial CT images demonstrate two focal areas of subtle hyperattenuation in the right parietal and left superior temporal lobe with adjacent edema.
T2 (Figure 3 and Figure 4), FLAIR (Figure 5 and Figure 6), and post-gadolinium T1 weighted (Figure 7 and Figure 8) MR images demonstrate two lesions located near the grey white junction with a small surrounding zone of edema and ring enhancement. No additional lesions were seen. There was no evidence of restricted diffusion.
Figure 9: The spectrum from the lesion shows no significant elevation of the choline peak, no depression of the NAA, and no lactate peak.
Diagnosis: Multiple fungal abscesses secondary to blastomycosis dermatitidis
The differential diagnosis for multiple ring enhancing lesions includes
- Metastatic disease
- Primary neoplastic processes
MRI spectroscopy is a powerful tool to help differentiate these entities in cases where the clinical and conventional imaging findings are equivocal.
Blastomycosis is an endemic organism in the southeast region of the United States usually contained within moist soil. Infection results from inhalation of the organisms which then transform to the yeast. Acutely cases may mimic bacterial pneumonia. Chronically, the disease can present in the lungs, urinary tract, skin, and occasionally with CNS involvement. CNS and severe pulmonary infections are treated with Amphotericin B.
Ring enhancing lesions on MRI have a long differential. Some use the mneumonic “Magical Dr” to help remember the etiologies. These include: Metastatic disease, Abscess, Glioblastoma multiforme, Infarction, Contusion, Aids (toxo), Lymphoma, Demyelination, and Radiation. Each of these entities can have similar imaging features on conventional MRI, however, the constellation of findings can help differentiate between the cases. In cases where the findings are equivocal, advanced techniques such as MR spectroscopy and perfusion imaging may help arrange the differential diagnosis appropriately.
MR spectroscopy of a tumor characteristically shows elevation of the choline to creatine ratio, elevation of the choline to NAA ratio, and frequently will have a lactate peak suggesting necrosis. While some inflammatory lesions can have a similar spectra such as multiple sclerosis, the lack of any significant spectral abnormalities in this case suggests a benign process. Very few processes that have post contrast ring enhancement have a relatively normal MR spectrum.