Ref: Nelson's Textbook of Pediatrics, 19th edit ion. Pages 2049 and 2052Explanation:HOUNSFIELD SCALEIt is a quantitative scale for describing radiodensity.The Hounsfield scale applies to medical grade CT scans.A change of one Hounsfield Unit (HU) represents a change of 0.1% of the attenuation coefficient of water since the attenuation coefficient of air is nearly zero.It is the definition for CT scanners that are calibrated with reference to water.The HU of various substances and organsSubstance/OrganHounsfield Unit (HU)Air-1000lung-500Fat-100 to -50Water0CSF15Kidney30Blood+30 to +45Muscle+ 10 to +40Grey matter+37 to +45White matter+20 to +30Liver+40 to +60Soft Tissue. Contrast+100 to +300Bone+700 (cancellous bone) to +3000 (dense hone)* So. -50 to -60 HU is suggestive of Tat' in the renal lesions.Characteristics of caseCharacteristics of the CaseFamilialAngiolipomatosisADPKDVHLTuberousSclerosisAge of 8 yearsNo (Presents in 3rd lo 5th decade)No (Presents in 4th to 6th decade)YesYesMental ReiaftlulionNoNoNoYesRenal Lesions (containing fat)Yes (But extremely rare)No (Renal cysts)NoYes(Angiomyolipoma of kidney)Liver Lesions (coniainirte fat)Yes (But extremely rare)No (Liver cysts)No(Liver cysts)Yes(Angiomyolipoma of liver)TUBEROUS SCLEROSIS (BOURNEVILLE'S DISEASE, EPILOA)Autosomal dominant inheritance.Mutations in TSC-1 gene at 9q - encodes Tuherin.Mutation nTSC-2 gene at 16 p - encodes Hamartin.Cutaneous LesionsAdenoma sebaceum (Facial angiofibromas).Ash leaf-shaped hypopigmented macules. Shagreen patches. Depigmented nevi.Neurological LesionsSeizures.Mental retardation.Autism.Calcified subependymal nodules.Ependymomas and childhood astrocytomaso >90% are subependymal giant cell astrocytomas.o These are benign neoplasms that may develop in the retina or along the border of the lateral ventricles.o They may obstruct the foramen of Monro and produce hydrocephalus.Candle dripping appearance in MRI.Renal ManifestaionsRenal cysts.Renal cell carcinoma.Angiomyomas of the kidney.Other ManifestationsAngiomyomas in:o Liver.o Adrenalso Pancreas.Rhabdomyomas of the myocardium.Pulmonary lymphangioliomyomatosis.m-TOR inhibitor Rapamycin, Minocycline are tried.VON HIPREL-LINDAU DISEASEAutosomal dominant inheritance.Mutation in tumor suppressor gene. VHL.VHL gene is located on chromosome 3p25-p26 and encodes a protein (pVHL).Clinical Features:Hemangioblastomaso Cerebellar (Most common site)o Retinalo Spinal cord.Cystic lesions of the kidneys, pancreas, liver and epididymis.Pheochromocytoma.Renal carcinoma (Most common cause of death in VHL).Polycythemia.FAMILIAL MULTIPLE LIPOMATOSIS (FML)Autosomal dominant inheritance.Very rare entity that is characterized by:o Numerous, encapsulated lipomas on the trunk and extremities.It generally affects consecutive generations within families.Multiple, well-encapsulated, oval-to-round, subcutaneous, rubbery lipomas.Size ranged from a few millimeters to 25 centimeters.Lipomas first appear in the 3 - 5th decades of life.Most commonly on the trunk and extremities.The forearms are a site of frequent occurrence.Visceral lesions are extremely rare.