Get all the keys from a hierarchical hash

I have a multi-tier hash (see below) and I'd like to be "search" the hash for a given $id, and return that section, regardless of how many layers deep it is. Sort of like how xpath works? Once I have that I'd like get ALL the children of a given node. So I could ask for 86, and get 36, 38, 56, etc and all THEIR children. Basically I want *all* the ID #s that are children. Array ( [88] => Array ( [109] => ) [86] => Array ( [36] => Array ( [8] => [121] => [127] => [135] => [144] => [161] => [165] => ) [38] => Array ( [18] => [39] => [156] => [158] => [182] => ) [56] => [97] => [107] => Array ( [240] => ) [115] => [123] => [146] => [149] => [223] => ) [157] => Array ( [3] => Array ( [5] => Array ( [11] => ) [13] => Array ( [6] => [7] => [98] => Array ( [81] => ) ) [111] => Array ( [10] => [17] => [110] => ) ) [148] => Array ( [9] => [87] => [102] => [104] => [114] => [130] => [133] => [160] => [201] => [237] => [238] => ) ) )