for 8.1+ postgresql

select gist_tree(INDEXNAME);
select gist_tree(INDEXNAME,MAXLEVEL);
select gist_stat(INDEXNAME);


example from gmake installcheck on rtree_gist:
select * from gist_print('pix') as t(level int, valid bool, a box);

# select * from gist_print('pix') as t(level int, valid bool, a box) where level < 2;
 level | valid |              a              
-------+-------+-----------------------------
     1 | t     | (37357,50073),(34242,357)
     1 | t     | (43499,49770),(40358,43)
     1 | t     | (31193,24679),(25047,12410)
     1 | t     | (31018,12142),(25083,6)
     1 | t     | (49944,25174),(43471,12802)
     1 | t     | (12577,49757),(6302,37534)
     1 | t     | (12528,37333),(6171,24861)
     1 | t     | (50027,49751),(46817,25462)
     1 | t     | (46870,49912),(43664,25722)
     1 | t     | (24855,25574),(12447,19263)
     1 | t     | (25054,19126),(12403,12796)
     1 | t     | (32737,49923),(31178,1038)
     1 | t     | (3184,24465),(15,81)
     1 | t     | (24951,49983),(12740,44000)
     1 | t     | (24919,43956),(12617,37901)
     1 | t     | (40387,49852),(37338,25217)
     1 | t     | (40325,24963),(37375,491)
     1 | t     | (24919,12698),(12654,6518)
     1 | t     | (25002,6338),(12350,51)
     1 | t     | (49985,12554),(43447,222)
     1 | t     | (25003,37769),(12552,25573)
     1 | t     | (34270,49382),(32763,594)
     1 | t     | (6205,50012),(3,37527)
     1 | t     | (6163,37358),(120,25034)
     1 | t     | (12343,24542),(9295,294)
     1 | t     | (9308,24151),(6234,620)
     1 | t     | (6230,24629),(3169,108)
     1 | t     | (31179,50040),(28113,25556)
     1 | t     | (28048,49694),(25000,25000)
(29 rows)