Schwannoma is a usually benign tumor that develops from Schwann cells, which are responsible for forming the protective covering around nerves called the myelin sheath. These tumors can occur along any peripheral nerve in the body but are most commonly found in the head, neck, and extremities. A well-known type is vestibular schwannoma, which affects the nerve responsible for hearing …

Postherpetic Neuralgia (PHN) is a chronic nerve pain condition that can occur after a shingles (herpes zoster) infection. It results from damage to the nerves caused by the varicella-zoster virus, which also causes chickenpox and shingles. PHN is characterized by persistent pain in the area where the shingles rash occurred, even after the rash has healed. It is more common …

Nephrotic syndrome is a kidney disorder characterized by excessive loss of protein in the urine due to damage to the filtering units of the kidneys, known as glomeruli. This loss of protein leads to low levels of protein in the blood and causes fluid to leak into body tissues. Nephrotic syndrome can occur in both children and adults and may …

Nephrogenic systemic fibrosis is a rare but serious condition characterized by thickening and hardening of the skin and connective tissues. It occurs almost exclusively in people with severe kidney dysfunction, particularly those with advanced chronic kidney disease or acute kidney failure. The condition has been strongly associated with exposure to certain gadolinium-based contrast agents used during magnetic resonance imaging scans. …

Nasal polyps are soft, painless, noncancerous growths that develop on the lining of the nasal passages or sinuses. They result from long-term inflammation and are often associated with conditions such as chronic sinusitis, asthma, or allergies. Nasal polyps vary in size and may occur in clusters, potentially blocking airflow and normal sinus drainage when they become large. Symptoms Small nasal …

Nasal and paranasal tumors are abnormal growths that develop in the nasal cavity or the paranasal sinuses, which are air-filled spaces around the nose. These tumors can be benign or malignant and are relatively rare. Because the nasal cavity and sinuses are close to the eyes, brain, and important nerves, even noncancerous tumors can cause significant symptoms if they grow …

Narcissistic personality disorder is a mental health condition characterized by a persistent pattern of grandiosity, an excessive need for admiration, and a lack of empathy for others. People with this disorder often have an inflated sense of self-importance and believe they are superior, while being highly sensitive to criticism. Narcissistic personality disorder typically begins in early adulthood and can significantly …

A quadriceps tendon tear is a musculoskeletal injury involving a partial or complete rupture of the tendon that connects the quadriceps muscle group to the top of the kneecap (patella). This tendon plays a critical role in straightening the knee and supporting movements such as walking, running, and jumping. Quadriceps tendon tears are more common in middle-aged and older adults …

Quadrantanopia is a visual field defect in which one-quarter of the visual field is lost in one or both eyes. It usually results from damage to specific parts of the brain involved in visual processing rather than a problem with the eyes themselves. The condition can affect daily activities such as reading, driving, and navigating surroundings, depending on which quadrant …

Q fever is a zoonotic infectious disease caused by the bacterium Coxiella burnetii. It primarily affects animals such as cattle, sheep, and goats, but humans can become infected through exposure to contaminated environments. Q fever occurs worldwide and can present as either an acute or chronic illness. While many infections are mild or asymptomatic, some cases can lead to serious …