Human immunodeficiency virus (HIV) infection compromises immunity of human body and the complicated opportunistic infections and AIDS-related malignant neoplasms are common causes of death in patients with AIDS. The diagnostic imaging can help to define AIDS-related diseases timely, which is important for timely therapeutic interventions and decreasing death rate. AIDS related diseases can involve the central nervous system, respiratory system, digestive system, bones and soft tissues, which is in different fields of diagnostic imaging. The diagnosis of opportunistic infections is an important field in diagnostic imaging. The pathogens include bacteria, viruses, fungi and protozoa. Pneumocystis carinii often involve lungs; cytomegalovirus invades lung and brain; herpes simplex virus and toxoplasma gondii cause intracranial infection; tuberculosis can simultaneously involve multiple sites. Opportunistic infection is most commonly found in lungs, with chest X-ray and CT scanning demonstrating morphologically different imaging findings. There are imaging demonstrations of ground glass liked density, parenchymal changes, nodules, cavities and lymphadenectasis. The opportunistic infections of the nervous system can be diagnosed by CT scanning and MRI imaging. HIV can cause AIDS related encephalopathy by passing through blood brain barrier, which may develops into progressive brain atrophy. Gastrointestinal tract and abdominal organs are also susceptible to a variety of pathogenic infections. Soft tissues infection of extremities are commonly caused by group A streptococcus and staphylococcus aurous, leading to purulent lesions such as cellulitis. Infections of bones and joints include osteomyelitis and septic arthritis. AIDS related malignancies can be demonstrated a space-occupying effect by the diagnostic imaging of the corresponding tissues or organs, in which Kaposi’s sarcoma and Non-Hodgkin’s lymphomas are the most common. The incidence of other neoplasms is also higher than the general population. For instances, in the low age group sustaining HIV infection, the occurrence of pulmonary carcinoma increases. Some diseases have obviously higher occurrence in patients with AIDS than in the general population, which can be used as the indicator disease of AIDS, such as penicilliosis marneffei, Kaposi’s sarcoma and non-Hodgkin’s lymphoma. Some imaging findings are common in AIDS related diseases, such as the diffusive lesions in lungs and brain, multiple enlarged lymph nodes, multiple organs lesions and imaging findings that are less common in the general patients. When these diseases or imaging findings are found, HIV infection should be considered in the differential diagnosis. The appropriate diagnostic imaging is favorable for timely detection and diagnosis of diseases. Due to the limited value of chest X-ray in the early detection of pulmonary opportunistic infections, clinical symptoms with negative chest X-ray findings should be further examined by CT scanning. CT scanning can facilitate the demonstrations of intra-pulmonary ground-glass density shadows, small nodules and enlarged lymph nodes. CT scanning can help to further analyze the non-specific changes demonstrated by chest X-ray. And CT scanning with high resolution is necessary for the differential diagnosis of intrapulmonary small lesions and diffusive lesions. Lesions in the brain can be diagnosed with CT scanning as the first choice, but MRI has more favorable sensitivity to lesions. Based on these diagnostic imaging, some special techniques are sometimes needed, such as MR spectroscopy, single photon emission computed tomography (SPECT) and magnetic transfer contrast imaging, for facilitative examinations and early diagnosis of AIDS. MRI can favorably show the range and depth of soft tissue infections, and necrosis; multislice spiral CT and its restructuring techniques contribute to findings and diagnosis of the chest and abdomen diseases; digitized X-ray has improved demonstrations of chest X-ray films and gastrointestinal radiography.

Due to compromised immunity of patients with AIDS, the imaging demonstrations of AIDS-related diseases are different from those of common diseases. Pulmonary tuberculosis is one of the AIDS-related diseases, occurring in 20 % patients with AIDS related pulmonary infections. In patients with severely compromised immunity and the CD4 count being less than 200/ul, AIDS related pulmonary tuberculosis has different imaging findings from common secondary TB in adults, but similar to primary TB. AIDS related TB commonly causes intra-thoracic lymphadenectasis. In addition, AIDS related TB has more atypical demonstrations in lesions locations and morphology, with more common findings of blood dissemination and bronchial dissemination. For AIDS related TB, extrapulmonary occurrence is up to 50 %, with involvement of peritoneum, liver, spleen, pancreas and gastrointestinal tract. However, in patients with non AIDS related TB, the occurrence of extrapulmonary TB is only 10–15 %, with primary manifestations of systemic lymph nodes tuberculosis including lymphadenectasis of superficial, pulmonary hilus, mediastinum and abdominal cavity. AIDS related bacterial pneumonia can have atypical manifestations, such as diffusive lesions in both lungs by diagnostic imaging. AIDS related neoplasms occur in multiple locations, with occurrence of Kaposi’s sarcoma in lymph nodes, gastrointestinal tract and lungs, occurrence of non-Hodgkin’s lymphoma in 75 % AIDS patients during the progressive stage. Extracapsular extension is commonly seen in the central nervous system, gastrointestinal tract and bone marrow. Pulmonary manifestations are multiple nodules, parenchymal changes and pleural effusion. Differential diagnosis of AIDS related diseases is the premise for administration of a specific therapy. For the diagnostic imaging, infections should be firstly differentiated from neoplasms. Many scholars have focused attention on the image findings of these diseases and a comprehensive analysis of the imaging signs will facilitate the defining of the lesions range. Due to the multiple pathogens to cause infections, their imaging manifestations are mostly similar, presenting challenges for the differential diagnosis. It is therefore important to combine the diagnostic imaging and the clinics (including transmission route of HIV, clinical manifestations and signs, laboratory tests, immunity and therapeutic outcomes) to diagnose and differentially diagnose AIDS related diseases. CD4 count is an indicator of immunity. Different CD4 counts indicate the hosts susceptible to different diseases with different manifestations. Before etiological and histological examinations findings, the preliminary diagnosis can be made based on clinics and the diagnostic imaging, which will facilitate the early therapeutic intervention.

X-ray is the most commonly used imaging technique in clinical practice. Chest X-ray can help to know the development of thymus and pulmonary infections. Anterioposterior and lateral chest X-ray for children under 12 months old can find thymus shadow on the surface of major blood vessels in unilateral or bilateral mediastinum. Lateral observation can find that thymus shadow is immediately behind the sternum, inside the anterior mediastinum and upper mediastinum. For children under 12 months old, invisible thymus shadow by chest X-ray indicates severe cellular immunodeficiency or combined immunodeficiency. But for children aged above 12 months or elder, chest X-ray bears unfavorable findings. Instead, special examinations such as mediastinal pneumography, mediastinal ultrasonography, CT scanning, MRI imaging and isotope scanning can be used to examine the development of the thymus. Chest X-ray may find the abnormalities in patients with pulmonary infections, such as bronchiectasis, interstitial pneumonia and lobular pneumonia. Pneumocystis carinii pneumonia is common disease in patients with AIDS or with severe immunodeficiency. By chest X-ray, the demonstrations are symmetrical blurry infiltration shadows surrounding pulmonary hila. For serious cases, the lesions can involve the middle lateral areas of both lungs. In patients with AIDS, the lungs can be obviously abnormal or close to normal in the early stage, with following occurrence of (1) lobar or lobular parenchymal lesions; (2) ground glass liked lesions; (3) singular or multiple nodular lesions; (4) cavitations; (5) hilar lymphadenectasis; and (6) pleural effusion. The lesions above can be concurrent. For some commonly seen diseases with unknown causes, AIDS related diseases or immunodeficiency should be considered.

For cases of immunodeficiency with accompanying esophageal candida infection, esophageal mucus is rough with unsmooth border. Esophagus is susceptible to cytomegalovirus infection. In such cases, esophageal mucosal folds are thickened, filling with defects and have occurrence of erosion or ulceration. Gastric cytomegalovirus infection may show lesions of stomach stenosis, granuloma, erosion or ulceration, thickened and stiff intestinal wall. Kaposi sarcoma and lymphoma occur commonly in gastrointestinal tract, with polypoid, ulcer-like, plaque or nodule-like lesions in sizes of several millimeters to several centimeters. The lesions have no significant specificity, whose definitive diagnosis should be based on barium meal, in combination with gastrointestinal endoscopy and pathological biopsy if necessary.