RESUMEN
BACKGROUND: Pathologic laughter is inappropriate, involuntary, and unmotivated laughter episodes that may or may not be associated with mirth or amusement. Although associated with many diffuse brain pathologies, its association with intracranial focal mass lesions causing ventrolateral brainstem compression, like petroclival meningioma, is very rare. The exact pathophysiology of this interesting and unusual clinical symptom is unknown, but probably involves disinhibition and release of the so-called coordination center located in the upper brainstem due to compression by the tumor. CASE DESCRIPTION: A 26-year-old woman presented with recurrent episodes of inappropriate and involuntary laughter, which significantly affected her quality of life, for 2 years. These episodes did not resolve, and a magnetic resonance imaging of the brain showed a giant petroclival meningioma causing upper brainstem compression. Near-total excision of the tumor was done using an extended middle fossa approach. To our surprise, the pathologic laughter subsided immediately after surgery. CONCLUSIONS: Pathologic laughter may be the only symptom of a focal mass lesion causing ventrolateral upper brainstem compression, like petroclival meningioma, well before other neurological sign/symptoms appear. Tumors causing ventral brainstem compression must be ruled out before the patient is sent for a psychiatric evaluation.