Kim Kardashian must be frustrated as her impending annulment case with estranged husband Kris Humphries shows no sign of getting resolved any time soon.But the reality star managed put her personal woes to one side last night as she jetted to Las Vegas to celebrate her brother Rob’s 25th birthday.The 31-year-old was in good spirits as she joined mother Kris Jenner and little sisters Kylie and Kendall for a wild night in Sin City’s Mirage Hotel.As expected, the brunette was in her usual figure-hugging style, showing off her famous curves in a cream sequinned dress. There was no missing her mother Kris, 56, who stood out from the crowd in a right bandage dress.Uploading photos on Twitter from in the club, it appeared Kris was the bigger party animal out of the two.Kim tweeted several photos of her mother dancing in a private booth, writing: ‘Mom gone wild... How pretty is my momma!?!’However, while teenagers Kylie, 14, and Kendall, 16, had jumped in the private jet for the mini excursion, they weren’t allowed to join the party at the 1 Oak club because they’re underage.Kim strictly stipulated the pair were only allowed to join them for dinner as she tweeted about their attendance: ‘Even the little sisters are coming to Vegas! #DinnerOnly.’When they were finally reunited with their mother and older siblings for their 3am flight back to LA, they made no secret of how bored they had been while waiting.Kendall tweeted in the early hours of this morning: ‘Longest night ever...’But Kim had clearly enjoyed herself: ‘3am flight back home! What a fun night!’Kim’s night out came as it was revealed she and estranged husband Humphries were still clashing in their annulment petition.They’re both willing to annul their 72-day marriage, but each are insisting the other should confess to ‘fraud’, according to TMZ.com.Kim is said to be claiming Kris promised to live with her in Hollywood before they wed, but then demanded she moved to Minnesota afterwards.And Kris accused Kim of not having any intention of having a real marriage, which she has vehemently denied.dailymail.co.uk