The Master muscles are used for chewing. When these muscles are immobilized with botulinum toxin, the Temporalis muscles are recruited to aid in chewing to compensate for the last of master function. This would actually cause a slight hypertrophy and filling in of the temples rather than hollowing.
Bruising can occur after Botox injection. Arterial or Venus puncture can result in a hematoma which can appear as a mass. Warm compress should help and you should follow up with your physician.
Botox is not used with the specific purpose of reducing muscle bulk; its function is to weaken (temporarily) the muscle function. Of course, it's possible that over time with consistent injections for maintenance, the muscle bulk may atrophy from disuse but that would likely take at least 4-6...
