The present invention provides monitoring means for monitoring the space and volume within a lower annulus. In particular, the monitoring means monitors the space and volume within the lower annulus 52 located between the inner surface of the 22 intermediate casing string 22 and the outer surface of the inner casing string 32. Furthermore, the monitoring means provides the capability to retrieve and/or introduce fluid(s) into the annular space 52. The monitoring means provides a port, specifically a passageway 100, which extends upwardly from the annular space 52 to an outlet located above the hanger 36 for the intermediate casing string 22. The passageway 100 is provided in a sleeve 102. The monitoring means includes a sensor located above the hanger 36 which means that the fluid in the annular space 52 can be monitored without the need for penetrating a casing in the wellhead.