Radiology in AIDS

Thoracic manifestations

 

Thoracic manifestations of AIDS can be divided into infectious and noninfectious entities, the latter including neoplastic and non-neoplastic diseases. The type of pulmonary manifestations seen in AIDS has evolved considerably; this is partly due to improvement in therapy, such as the widespread use of prophylaxis for Pneumocystis carinii pneumonia (PCP), while infection due to Mycobacterium tuberculosis has been rising at an epidemic rate, and the number of patients with Kaposi's sarcoma (KS) has been decreasing continuously.

 

a

Figure 7. Cystic PCP. Radiographic CT correlation. a) Posteroanterior chest radiograph shows the presence of diffuse pulmonary infiltration, predominantly distributed in upper and middle lung zones, associated with subtle, bilateral thin-walled cysts in the upper lobes. b) CT scans made through the carina at the same time as (a), shows that numerous cysts of various sizes and wall thickness are seen bilaterally in the upper lobes that are infiltrated with nodular and ground glass opacities. Subtle bilateral pneumothorax is also seen.

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Infectious diseases

Pneumocystis carinii pneumonia (PCP)
PCP is the most common pulmonary infection in patients with AIDS. This infection occurs at least once during the course of the disease in approximately 60% of AIDS patients, and nearly one-quarter of these initial episodes is fatal. In addition, the likelihood of severe recurrent infection occurs in between 20 and 40% of all cases. Radiographically, PCP appears as peripheral interstitial infiltrates that may progress within a few days to diffuse consolidation involving the entire lung. Atypical patterns, including focal parenchymal lesions, cavitary nodules, hilar and/or mediastinal adenopathy, pleural effusions and even a miliary pattern, occur in 5 % of the patients. They should prompt consideration of possible coexisting infections.

Figure 8. M. Tuberculosis. Posteroanterior radiograph shows consolidation in the upper part of the left upper lobe containing several cavities. This pattern is consistent with mycobacterium or bacterial infections.

An increasing number of patients also developing cystic lung disease demonstrated radiographically by the presence of air-filled cysts or pneumatoceles predominantly located in the upper lobes. The etiology of both these signs has not been firmly established, but there is a clear association between the presence of cystic abnormalities and the development of pneumothorax (Fig. 7). Calcified lymphadenopathy is increasingly common and seems to be related to prophylaxis with aerosol delivered pentamidine. Finally, in 10% of the cases, the chest radiograph will appear normal in patients with proven PCP. Although the radiograph remains the radiological standard of diagnosis, CT can show ground-glass densities even when the chest film has been interpreted as being normal. In addition, CT may show unexpected bronchial dilatation as well as cystic lung disease.

Mycobacterial infection
Infection with Mycobacterium tuberculosis occurs in about 10% of cases and its incidence is increasing every year. The radiologic appearance of tuberculosis reflects the degree of impairment of the immune system. When the deficiency is subtle, tuberculosis is usually indistinguishable from that which occurs in non-HIV-infected patients, with upper lobe cavitary infiltrates (Fig. 8). The more advanced the immunodeficiency is, the more suggestive of primary disease the radiographic pattern is, including adenopathy, effusion and diffuse infiltrates without evidence of cavitation. At this stage, the presence of extensive low-density mediastinal and hilar lymphadenopathy on contrast-enhanced CT scans is highly suggestive of the diagnosis of tuberculosis or fungal infection.

Pulmonary disease is relatively uncommon in patients infected with M. avium-intracellulare and usually occurs late in the course of HIV infection. The radiographic abnormalities include intrathoracic adenopathy, pulmonary infiltrates, nodules and a miliary pattern. Other atypical mycobacteria may cause pulmonary infection in AIDS is M. kansasii.

Bacterial infections
The incidence of bacterial infections in AIDS patients has risen sharply. It is currently estimated that 5-30% of AIDS patients develop bacterial pneumonia during the course of their disease.

In pyogenic infections, the radiograph typically shows lobar consolidation, nodules and focal infiltrates with or without an associated pleural effusion. However, some cases present with a predominant interstitial infiltrate which is indistinguishable radiographically from that usually associated with PCP infection. A prompt diagnosis of bacterial infection is necessary because most patients respond to routine antibiotic therapy. In some cases, CT can be of value by revealing foci of cavitation or necrosis, as well as documenting the presence of unsuspected loculated pleural effusions or bronchiectatic foci.

Fungal diseases
Fungal infections are uncommon, occurring in less than 5 % of AIDS patients. They include infections with Cryptococcus neoformans, Histoplasma capsulatum, Coccidioides immitis, Candida albicans and Aspergillus.

C. neoformans is the most common cause of fungal pulmonary infection in patients with AIDS. Chest radiographs may show a wide range of abnormalities but, in most patients, films are either normal or show focal parenchymal disease. In histoplasmosis, the chest radiograph is normal or shows disseminated nodular disease. In patients with coccidioidomycosis, films usually reveal a diffuse interstitial infiltrate often associated with thin-walled cavities. Aspergillus is rarely the cause of primary infection, however, secondary aspergillosis of cavities has been noted in association with PCP.

 

a	Figure 9. KS. a) Posteroanterior radiograph shows bilateral perihilar in filtrates predominantly distributed in middle and lower lung zones. b) CT scan through the lower lobes shows a typical pattern of tumours extending along perivascular and peribronchial pathways from the hila into the lung associated with a few, small, poorly defined peripheral nodules.
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Non infectious diseases

Kaposi's sarcoma (KS)
Almost all cases of KS in AIDS patients have been documented to occur in homosexual or bisexual men. It has been postulated that its development may be dependent upon an as yet undiscovered cofactor and may not be directly due to HIV infection, per se. Pulmonary involvement occurs in approximately 20% of the patients with AIDS-associated KS, and it is almost always preceded by cutaneous or visceral involvement. The radiograph shows bilateral infiltrates associated with characteristic poorly delineated nodules. Pleural effusions occur in up to one third of the patients and are typically serosanguineous. Lymphadenopathy develops in nearly 10% of cases and tends to be a late manifestation of KS. As diffuse interstitial infiltrates are non-specific and may be secondary to either KS or other entities, especially opportunistic infections, both CT and radionuclide imaging may be useful. On CT scans, the pulmonary involvement due to KS is seen as poorly defined peribronchial and perivascular densities, typically emerging from the hilum, associated with subpleural nodules and pleural effusions (Fig. 9). This highly characteristic distribution of the disease allows a presumptive diagnosis of parenchymal involvement in selected cases. Sometimes, CT scans show a pattern more consistent with lymphangitic carcinomatosis, probably reflecting involvement of central nodes. Since gallium rarely accumulates in KS patients, in those with KS and a coexisting opportunistic infection, gallium-67 scans may indicate the optimal site for biopsy or lavage. Bronchial erythematous plaques seen during bronchoscopy should be considered pathognomonic. The diagnosis can also be made based on a bronchial biopsy. Because chemotherapy can achieve short term palliation, bronchoscopy, bronchoalveolar lavage and scans should be performed in an attempt to diagnose KS.

Lymphocytic interstitial pneumonitis (L/P)
LIP occurs in patients with AIDS and is considered a disease indicator when confirmed histologically in children under 13 years of age or if documented in HIV -positive adults. The cause of LIP is unknown and could possibly be an indirect immune response to pulmonary infection by HIV. Radiographically, LIP is seen as fine and coarse diffuse, non specific reticular or reticulonodular opacities with or without superimposed patchy foci of airspace consolidation. These findings are typically indistinguishable from those of other opportunistic infections. Adenopathy and pleural effusions are usually absent. Diagnosis requires an open lung biopsy. As in non AIDS patients, progression to lymphoma is unusual.

AIDS-related lymphoma (ARL)
The incidence of ARL is clearly increasing. These tumours have a tendency to be highly aggressive, displaying poorly differentiated histologic subtypes associated with a poor prognosis. In most cases, AIDS is at an advanced state at the time of ARL diagnosis. The tumours are primarily extranodal in distribution and thoracic sites are relatively less common than those in the central nervous system, gastrointestinal tract, liver, spleen and bone marrow. ARL usually manifests itself as either solitary or multiple well-defined pulmonary masses, or as a focal parenchymal infiltrate, often in association with pleural effusions and frequently without mediastinal or hilar disease. These findings are non specific and may also be seen in patients with fungal infection or other tumours, including KS or solid tumors. The definitive diagnosis usually requires histologic confirmation.

Diagnosis and role of imaging
AIDS patients suspected of having pulmonary disease usually undergo fibreoptic bronchoscopy, particularly when a non-infectious etiology is suspected. Bronchoscopic investigation includes bronchoalveolar lavage sometimes in conjunction with transbronchial biopsy. In some cases, the initial bronchoscopic findings are non-diagnostic and further monitoring is required, including the patient's clinical status and radiologic findings. Gallium scintigraphy can be indicated to determine if active disease is present. In the case of clinical or radiological deterioration, patients should undergo a repeat bronchoscopy. Patients with focal lung disease may benefit from thoracic needle biopsy. The role of open lung biopsy is more controversial. However, surgery may be indicated specifically for patients in whom no diagnosis has been established. CT can help to: a) identify occult pulmonary disease including areas of ground-glass opacity in early PCP as well as occult tuberculous infection; b) differentiate PCP from KS and lymphoma; c) identify the low-density lymphadenopathy in patients with tuberculosis; d) guide transthoracic needle biopsy.

 

Marie-France Bellin, Philippe Grenier and Nadine Martin- Duverneuil