Rare causes of pulmonary hypertension. Spectrum of radiological findings and review of the literature

Following a brief introduction covering the clinical signs and symptoms of pulmonary hypertension (PH), its most recent classification into six groups, and the computed tomography (CT) features common to all forms of PH, this paper illustrates the typical patterns that can be found on chest radiography and CT in rare causes of PH. We present and compare with the existing literature our personal series of cases of rare forms of PH, found in the following diseases: veno-occlusive disease, pulmonary capillary haemangiomatosis, non-thrombotic pulmonary embolism (tumour embolism and carcinomatous lymphangitis, talcosis, hydatid disease), pulmonary artery sarcoma, neurofibromatosis, sarcoidosis, and Langerhans cell histiocytosis. Rare forms of PH show low incidence and prevalence, and are, therefore, poorly recognised. Their diagnosis is a challenge for clinicians, pathologists, and radiologists, and any additional knowledge about the CT findings may help the diagnosis in the case of patients affected by PH of unknown origin.