rhombocele

rhom·boi·dal si·nus

, sinus rhomboidalis
a dilation of the central canal of the spinal cord in the lumbar region.
Synonym(s): rhombocele

rhomboidal sinus

(1) Cavity of septum pellucidum; cavum septi pellucidi [NA6]. 
(2) Terminal ventricle of spinal cord; ventriculus terminalis medullae spinalis [NA6]

rhom·boi·dal si·nus

, sinus rhomboidalis (rom-boy'dăl sī'nŭs, rom'boy-dā'lis)
A dilation of the central canal of the spinal cord in the lumbar region.
Synonym(s): rhombocele.

rhombocele

(rŏm′bō-sēl) [″ + koilos, a hollow]
The cavity of the rhombencephalon.