Marfan Syndrome: This genetic disorder is known for causing arachnodactyly (spider-like fingers) and can lead to hemorrhagic brain lesions due to its effects on blood vessels, including the risk of aneurysm formation and rupture.

Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues. Its vascular type can lead to rupture of arteries, including those in the brain, and some forms may present with arachnodactyly.
Pseudoxanthoma Elasticum (PXE): A genetic disorder that affects the elastic fibers present in the skin, retina, and cardiovascular system. It can lead to vascular complications, including hemorrhages, and may present with features that could be confused with arachnodactyly due to skin and joint laxity.

Neurosurgical Emergencies (e.g., Aneurysm, Arteriovenous Malformation): While not directly related to arachnodactyly, any hemorrhagic brain lesion requires immediate consideration of neurosurgical emergencies that could be deadly if not promptly addressed.
Vasculitis: Inflammation of the blood vessels that can lead to hemorrhagic lesions in the brain. It's crucial to consider vasculitis in the differential diagnosis due to its potential for severe and widespread vascular damage.

Homocystinuria: A genetic disorder that affects the metabolism of the amino acid methionine and homocysteine. It can lead to vascular complications, including thrombosis and potentially hemorrhage, and may present with features similar to Marfan syndrome, including arachnodactyly.
Sturge-Weber Syndrome: A rare disorder characterized by a port-wine stain (a birthmark) on the face, neurological abnormalities, and vascular malformations, including those that could lead to hemorrhagic brain lesions. Arachnodactyly is not a primary feature but could be considered in a broad differential for syndromic conditions affecting vascular and connective tissue.