Absent kidney can be due to surgical removal or it can also occur genetically and is then called renal agenesis.

An accessory spleen is a small nodule of splenic tissue which is not connected to the rest of the spleen. They are benign and asymptomatic.

Usually there are two renal arteries that branch off from the abdominal aorta (the main blood vessel that exits the heart and brings oxygen-rich blood to the rest of the body). An accessory "extra" renal artery is a common variant of the renal arteries. They are common findings in approximately 25% of the population.

Lymph nodes filter substances that travel through the lymphatic fluid, and they contain lymphocytes (white blood cells) that help the body fight infection and disease. There are hundreds of lymph nodes found throughout the body. The perirectal lymph nodes are located around the rectum and drain parts of the colon and the upper part of the rectum. Sometimes lymph nodes are noted on imaging to be prominent (enlarged). Anything that causes inflammation can cause enlarged lymph nodes, including viral and bacterial infections. Usually enlarged lymph nodes do not cause symptoms, are self-resolving and do not need any further follow-up. If symptoms are present they could include abdominal/pelvic pain and/or weight loss.

The acetabulum is the socket of the hipbone, into which the head of the femur (thigh bone) fits. A labrum is a cup-shaped rim of cartilage that lines and reinforces a ball-and-socket joint. Ossification is the process of bone remodeling. When a fracture occurs, the body’s healing and remodeling process can have a typical appearance on imaging. If a labrum is injured (e.g. torn) it can become hardened, calcified, and even turn into bone (ossified). Os acetabuli are unfused ossifications at the upper acetabular margin. All of these indicate an increased probability of impingement of the hip joint. The result is increased friction during hip movements that may damage the joint.Symptoms include pain in the groin after prolonged sitting or walking. Many athletes often describe pain in the groin with deep flexion or rotation of the hip during activity. Occasionally, a popping or clicking in the front of the hip is described. Pain may also radiate along the side of the thigh and in the buttocks.

An acoustic schwannoma (also known as acoustic neuroma or vestibular neuroma) is a benign tumor that develops around a nerve in the inner ear. This tumor grows around and compresses either the auditory (cochlear -for hearing) or vestibular (for balance) nerves leading from your ear to the brain.

Paranasal sinuses are a group of air-filled spaces that surround the nasal cavity: the maxillary sinuses are located under the eyes, the frontal sinuses are above the eyes, the ethmoid sinuses are between the eyes and the sphenoid sinuses are behind the eyes. Indications of acute sinusitis (inflammation of the sinuses with symptoms lasting less than four weeks) that are seen on imaging include the presence of air-fluid levels and/or a "bubbly or foamy" appearance of the sinuses.

There are two adrenal glands in the body, one on top of each kidney. The adrenal glands make hormones that regulate the body’s metabolism, response to stress, and salt and water balance. Adrenal nodules (adenomas) are growths inside these glands and are estimated to be present in 1-9% of people. Nodules smaller than 4 cm are most common and usually benign (non-cancerous). Nodules greater than 4 cm in size require further evaluation. Adrenal nodules are usually asymptomatic, but sometimes can overproduce hormones and cause symptoms including: changes in face and body shape, acne, unexplained weight gain or loss, high blood pressure, diabetes, muscle weakness, increase in body hair in women, excessive sweating, abnormal fatigue, and sexual dysfunction.Adenomas contain lipids (fatty content), and when more than 80% of its contents are lipids, they are considered lipid-rich.

There are two adrenal glands in the body, one on top of each kidney. The adrenal glands make hormones that regulate the body’s metabolism, response to stress, and salt and water balance. Calcium can deposit inside healed scar tissue anywhere in the body, and this finding suggests that there was past damage to the adrenal gland.

An adrenal myelolipoma is a rare, usually unilateral (found in only one adrenal gland and not the other), benign (non-cancerous) tumor. It is composed of mature fat cells and interspersed hematopoietic cells (cells that give rise to other blood cells) that resemble bone marrow. On imaging, the presence of large amounts of fat in an adrenal mass is diagnostic of a myelolipoma. Most lesions are asymptomatic (do not cause symptoms) and may be discovered incidentally when the region is imaged for other reasons.