Extrapulmonary Aspergillosis

The paranasal sinuses are quite a common site for Aspergillus infections of patients in the tropics. The underlying histopathology is a sclerosing granuloma which occurs most frequently in the Sudan, India, and the Middle East. There may at first be only a simple aspergilloma in the sinus, but often the infection is invasive and proptosis develops as the fungus spreads from the adjacent sinus. On imaging, there is usually opacification of one or more sinuses. The disease is slow and painless, but CT particularly will show early periosteal reaction causing sclerosis of the antral wall next to the soft tissue granuloma. This closely mimics malignancy, particularly as the "tumor" spreads.

An infection by A. flavus (in the Sudan as well as elsewhere) may cause bone destruction which is irregular but quite well defined. Spread may be in any direction, medially or laterally or upwards into the floor of the orbit. CT and MR scanning are very important when there is upward spread, because the frontal bones and meninges may be penetrated and intracranial aspergillosis can be quite extensive (and fatal). Such infections show low attenuation and variable contrast enhancement. MRI will help in the differentiation between paranasal aspergillosis and neoplasm. Aspergilloma has a low T2-weighted signal intensity (due to the high iron and manganese content in fungi). Fungi in the nongranulomatous stage have a high T2-weighted signal, as do other inflammatory masses compared with most neoplasms, which show an intermediate signal, with a few giving a high T2-weighted signal. CT and MRI are thus excellent ways to show the extent of bone and soft tissue involvement and should be used whenever spread from the sinuses is suspected (Fig. 6.35). If scanning is not available, linear tomography will also be very helpful. There are almost always large soft tissue polyps and CT (or linear tomography) will demonstrate these. There may be similar polyps within the nose. If the infection spreads downwards, the teeth may be disrupted and appear to "float." In children in some parts of the tropics, Burkitt's lymphoma will have to be excluded as a cause of both proptosis and teeth displacement. In chronic aspergillosis there will be more bone sclerosis, and linear calcification has been reported, most commonly in recurrent infections: neither is likely in Burkitt's lymphoma (see Chap. 41).

Aspergillosis in other sites has no specific imaging characteristics. The granulomas or abscesses may be recognized by scanning, but in almost every patient the clinical and laboratory diagnosis has already been made.

Aspergillosis of the central nervous system may occur from hematogenous spread or, as noted, from direct invasion from the paranasal sinuses. Occasionally aneurysms develop because of fungal infarction. Aspergillus granulomas can be recognized on both CT and MR scanning, and are ring enhancing, mimicking tuberculosis, tumors, or other abscesses. Unfortunately, CSF culture following lumbar puncture is usually negative and the diagnosis must be made by tissue biopsy.

Cardiac aspergillosis is very rare and usually indicates immunodepression. Aspergillosis has been cultured from prosthetic valves and spread of the fungus from a valve has caused myocardial abscesses: echocardiography provides helpful information, which will demonstrate these complications in a known case of aspergillosis. As with the CSF, diagnostic blood cultures have a very low positive yield. Although of little significance for imaging, Aspergillus spp (usually A. niger) are often present in ear infections: this may be one of the few places in which it can be easily and successfully treated, but occasionally it becomes invasive and spreads into the temporal bone or mastoid. The destruction can be demonstrated by imaging, but as elsewhere, a definitive diagnosis cannot be made, although the clinician's worst fears may be confirmed.