<unk>  (also known as " Solitary<unk> " or "SPN") is defined as a relatively well defined round or oval pulmonary parenchymal lesion equal or smaller than 30 mm in diameter.<unk>  is usually surrounded by pulmonary parenchyma and/or visceral pleura and is not associated with lymphadenopathy, atelectasis, or pneumonia.<unk>  may be classified according to size (> 8 mm vs. ≤ 8 mm), attenuation (pure solid vs. part-solid), and distribution (solitary vs. multiple). It can also be classified into benign and malignant based on the radiological findings.Causes of<unk> s can be classified into etiologies presenting with solitary or multiple lesions. Common causes of solitary<unk>  include tuberculosis, primary lung cancer, granuloma, and rheumatic disease. Common causes of multiple<unk> s include pulmonary neoplasms and tumor metastasis from other parts of the body.<unk>  may be differentiated according to imaging (size, border characteristics, and attenuation), histological, and clinical features, from other diseases that demonstrate similar imaging findings. Common differential diagnoses of<unk>  include hamartoma, granulomas, rheumatoid nodule, and metastatic lesions.<unk> s are common. The estimated prevalence of incidental<unk>  ranges between 0.09% to 7% in the general population. The incidence rate of<unk>  increases with age, tobacco use, and prior cancer; the median age at diagnosis is between 35 to 70 years. The prevalence of malignancy among<unk> s ranges between 0.2% to 50%. Males are more commonly affected with<unk>  than females. The male to female ratio is approximately 2 to 1. There is no racial predilection to<unk> . According to the U.S. Preventive Services Task Force (USPSTF), screening for suspected lung cancer by low-dose computed tomography is recommended every year among smokers who are between 55 to 80 years old and who have smoking history of 30 pack years or more and either continue to smoke or have quit within the past 15 years (grade B recommendation). A hallmark feature in the evaluation of<unk>  is the malignancy risk assessment. The evaluation approach for<unk>  will mainly depend in the initial morphological evaluation of the nodule (size, margins, contours, and growth). Other characteristics, such as location, clinical features, and distribution may be helpful in the risk assessment, management, surveillance, and follow-up of<unk> .<unk>  can be divided into 3 risk categories: low risk, intermediate/moderate, and high risk. Based upon these risk categories, complementary diagnostic studies and management include: PET/CT scan, CT scan, non-surgical biopsy, and surgical resection. Lung biopsy is the study of choice to diagnose<unk> . Biopsy for<unk>  may be classified into 2 categories: non-surgical biopsy and surgical biopsy. Biopsy findings associated with<unk>  will depend on tumor histology. Common types of lung tissue biopsy for solitary<unk>  include conventional bronchoscopic-guided transbronchial biopsy, bronchoscopic-transbronchial needle aspiration, endobronchial ultrasound-guided sheath transbronchial biopsy, and endobronchial ultrasound-guided transbronchial needle aspiration. Common indications for biopsy in<unk>  include: high risk nodule (> 65%), intermediate risk nodule with a high risk patient profile, intermediate risk nodule with a positive positron emission tomography scan.<unk> s are generally asymptomatic. In some cases, patients may develop non-specific symptoms, such as difficulty breathing, hemoptysis, chronic cough, wheezing, and chest pain. Obtaining a detailed history is an important aspect of making a diagnosis of solitary<unk> . Specific areas of focus when obtaining history include previous infection of tuberculosis, previous or current smoking history, history of immunological conditions, high occupational risk profession, or recent traveling. Patients with<unk>  usually are well-appearing. Physical examination of patients with<unk>  usually has no remarkable findings. In some cases, solitary<unk>  may show findings associated with the underlying condition. There are no diagnostic laboratory findings associated with<unk> . There are no ECG findings associated with<unk> . On conventional radiography, characteristic findings of solitary<unk>  include well-defined, small, and rounded opacities within the pulmonary interstitium, usually 8 mm in diameter and normally surrounded by normal aerated lung. There are no echocardiography/ultrasound findings associated with<unk> . CT scan is the method of choice for the diagnosis of solitary<unk> . On CT, characteristic findings of solitary<unk> s include ground-glass opacity, rounded mass, and less than 30 mm in size. The evaluation of solitary<unk>  will depend on the following characteristics: calcification pattern, size, location, growth, shape, margins, attenuation, and contrast enhancement. On MRI, characteristic features of<unk>  include higher soft tissue contrast, lack of radiation exposure, lesion characterization by evaluation of signal intensities, and characterization of the dynamics of contrast uptake. Other imaging studies include PET/CT scanning, which may be useful as a staging modality, detection of occult disease, and malignancy assessment. Other diagnostic studies for solitary<unk>  include transthoracic percutaneous fine needle aspiration, bronchoscopy, and mediastinoscopy. The optimal management approach of solitary<unk>  mainly depends on the nodule size and growth. Other parameters, such as location and distribution may also be helpful. Surgical resection is often recommended among patients with a malignant likelihood of solitary<unk> . On the other hand, solitary<unk> s with benign features are eligible for periodic CT surveillance. Surgical excision is the mainstay therapy for malignant or high risk<unk> s. In<unk> , surgical procedure selection will depend on the size, margins, and size of the tumor. The preferred surgical procedure is wedge resection by video-assisted thoracic surgery and subsequent pathological evaluation. Primary prevention of solitary<unk>  includes avoidance of active and passive smoking, exposure to asbestos, and high risk occupational jobs. The American College of Chest Physicians (ACCP) and Fleischner Society guidelines offer a strategy to manage and follow up on<unk> .
Pulmonary nodule
Pulmonary mass
Lung mass
Multiple pulmonary nodules
Pulmonary metastasis
Pulmonary consolidation
Lung abscess
Parapneumonic effusion