A system includes a plug assembly having a housing configured to be positioned within a first passageway formed in a wellhead component. A channel is formed in the housing, and the channel is configured to enable fluid to flow from a bore of the wellhead component into the channel. A sensor is supported by the housing and is configured to measure a condition of the fluid within the channel. An annular seal is configured to extend between an outer surface of the housing and an inner surface of a second passageway formed in a flange that circumferentially surrounds at least part of the plug assembly while the flange is coupled to the wellhead component.