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May-Thurner syndrome occurs when the left iliac vein, which carries blood from your legs and pelvis back to your heart, is compressed by the right iliac artery.

Meckel's diverticulum is a small pouch in the wall of the intestine, near the junction of the small and large intestines. The pouch is a remnant of tissue from the prenatal development of the digestive system...

Mediastinal disease refers to an unusual group of tumors that form in the area called the mediastinum, which separates the lungs in the middle of the thoracic cavity. About half of mediastinal tumors cause no symptoms and are found on a chest X-ray or scans for another reason. Occasionally, they will cause symptoms of chest pain or shortness of breath.

Melanoma is the most serious type of skin cancer. It starts when the pigment-producing cells in your skin (melanocytes) become abnormal and grow out of control.

Memory disorders go beyond occasional forgetfulness, hindering one’s ability to make, retain, and retrieve memories. They can be the result of progressive neurological disease or sudden brain injury, and can range from mild to severe cognitive impairment...

A variety of illnesses are specific to men. Prostate problems, erectile/sexual dysfunction, depression and heart disease can all be interrelated. Typical concerns include: problems achieving and/or maintaining an erection sufficient for satisfactory sexual intercourse (ED); achieving an ejaculation too soon after penetration (premature ejaculation); lack or orgasm and/or ejaculation...

Learn about meningioma diagnosis, symptoms, causes and treatments at Northwell Health’s Brain Tumor Center.

A damaged meniscus can cause pain and swelling of the knee, particularly during physical activity. Though a torn meniscus may sometimes heal with only conservative treatment such as rest and reduced activity, in many cases the only lasting relief comes through a surgical operation known as a meniscectomy, most often performed using minimally invasive techniques.

Meniscus tears are fairly common knee injuries affecting the rubbery, crescent-shaped discs that provide cushioning between the knee bones. The meniscus is an important component of the knee; it offers shock absorption and contributes to the stability of the knee. A meniscus tear can keep the knee from functioning properly and greatly disrupt everyday life until it’s healed.

Menopause is a normal condition that every woman experiences (most commonly at age 51) when her ovaries no longer produce estrogen.

Learn about menorrhagia, also known as abnormal periods, and the treatment approach at Northwell.

Learn about common menstrual disorders, such as premenstrual syndrome, and how experts at Northwell Health treat and manage these disorders.

There are three different forms of mercury that cause health problems: elemental mercury (also known as liquid mercury or quick silver), inorganic mercury salts and organic mercury...

Mesenteric ischemia occurs when blocked arteries restrict blood flow to the small intestine, which can happen either over time (chronic) or suddenly (acute).

Mesothelioma is a rare form of lung cancer that usually arises in the tissue lining of the lungs, called the mesothelium. It usually starts in the lungs, but can also start in the abdomen or other organs. Most people who develop mesothelioma have worked on jobs where they inhaled asbestos particles.

Mesothelioma is a rare form of lung cancer that usually arises in the tissue lining of the lungs, called the mesothelium.

Methicillin-resistant Staphylococcus aureus (MRSA) is a type of Staph bacteria that is resistant to many antibiotics. There are two types of MRSA: Hospital-associated MRSA, which can cause infections in the bloodstream and at surgical sites and pneumonia Community-associated MRSA, which can cause skin or lung (less common) infections MRSA is often spread through direct contact with an infected wound...

Micropenis is defined as a normally structured penis that is below the normal size range for an infant. Normally, the length of a newborn boy's penis is between 2...

Learn more about miscarriage and Northwell Health’s comprehensive approach to the leading reason for pregnancy loss in the U.S.

Mitral valve prolapse (MVP) is the most common heart valve abnormality. In this condition, enough blood does not flow through the mitral valve into the coronary artery. If the leaflets (valve flaps) do not close tightly, blood can leak back into the heart’s chambers (left atrium and left ventricle), in a condition known as mitral regurgitation.

Valvular heart disease occurs when the heart's valves that control blood flow do not work properly. Valvular conditions can be present at birth or can be acquired later in life, resulting in valvular regurgitation (also known as valve insufficiency).

Valvular stenosis occurs over time as the opening in a valve narrows due to a collection of calcium deposits. When that happens, the heart cannot pump as well.

Learn about molar pregnancy, a complication that occurs during fertilization, and the treatment approach at Northwell.

Learn how behavioral health specialists at Northwell Health treat mood disorders.

Morton’s neuroma is a build-up of benign (non-cancerous) tissue in the nerves running between the long bones of the foot. Morton’s neuroma occurs when two bones rub together and squeeze the nerve between them...

Multiple birth is defined as twins or a higher order of multiples, including triplets, quadruplets, quintuplets, sextuplets, septuplets, etc.

Multiple myeloma (plasma cell neoplasm) is a rare type of cancer that results in the uncontrolled production of one type of white blood cell (plasma cell) in the bone marrow. The cancer cells can crowd out normal blood cells, causing a reduction in red blood cells (anemia).

Myasthenia gravis (MG) is an autoimmune disorder of the nerves and muscles of the body that causes progressive weakness and, often, drooping of the eyelids known as ocular myasthenia.

Myelodysplastic syndrome (MDS) is a group of blood diseases that cause an abnormally low production of blood cells. MDS is more common in older adults and rare in children and may develop before the start of a more serious blood disease, acute myelogenous leukemia.

Myeloproliferative neoplasm is a disease that affect blood cell formation. In all forms of myeloproliferative disorders, a bone marrow problem leads to increased levels of blood cells circulating in the bloodstream.

Chronic muscle pain caused by myofascial pain syndrome can be both relentless and debilitating. The causes of myofascial pain syndrome center around points in your muscles called trigger points...

Myofascial pain affects skeletal muscles that connect muscles to bones and help you move. It also affects the tissue (called fascia) that surrounds the muscles...

Myositis is a rare disease in which the immune system chronically inflames the body's own healthy muscle tissue. The muscles are progressively weakened by persistent inflammation...