Spinal Dysraphism: This condition, which includes a range of spinal anomalies, is the most likely diagnosis due to the presence of a sacral dimple and a tuft of hair. These signs are indicative of an underlying spinal defect, such as spina bifida occulta or a tethered cord, where the spinal cord becomes attached to the spine and can cause neurological problems.

Dermoid Cyst: A dermoid cyst, which can form along the spine, may present with a sacral dimple and associated hair, due to the abnormal collection of cells and tissues.
Lipoma: A lipoma, especially one associated with the spine, can cause a sacral dimple and may have overlying hair, due to its fatty tissue composition.
Teratoma: Although less common, a teratoma, which is a type of tumor containing several different types of tissues, could present similarly, especially if it involves the sacral area.

Tethered Cord Syndrome: This is a critical diagnosis not to miss, as it can lead to significant neurological deterioration if not addressed. The presence of a sacral dimple and tuft of hair could indicate a tethered cord, which requires surgical intervention.
Meningocele or Myelomeningocele: These conditions, where the meninges or spinal cord protrude through a defect in the spine, are critical to diagnose early due to their significant implications for neurological function and infection risk.

Neurenteric Cyst: A rare congenital anomaly where there's an abnormal connection between the intestine and the spinal cord, which could potentially present with a sacral dimple and hair.
Spinal AVM (Arteriovenous Malformation): Although rare, an AVM in the spinal region could potentially cause a sacral dimple and associated findings, including a tuft of hair, due to the abnormal vascular structure.