Case report: absence of the right piriformis muscle in a woman

Abstract

We report a very rare case of a unilaterally absent piriformis muscle in a 60 year old woman. Accompanying variations comprised a common gluteal artery (instead of two distinct superior and inferior gluteal arteries), and an absent gemellus inferior muscle. The contralateral left side showed a normally developed piriformis muscle. In hominoids, the piriformis is constant, but is regularly missing in several other vertebrates. The piriformis muscle is an anatomical landmark for ultrasound investigations and ultrasound-guided interventions in the deep gluteal region such as a superior gluteal nerve block or even a sacral plexus block, also for any surgical approach such as total hip arthroplasty. A missing piriformis muscle therefore affects the orientation in the deep gluteal region and therefore the identification of the targeted structures.

A rare muscle variation – accessory piriformis muscle

“…In the literature, there are several variations of the piriformis described -divided piriformis, cleavage of muscle bellies, merging with other muscles, or even absence. [4,5] The most important muscle variations, however, are those related to the structure of the proximal sciatic nerve. [6] Six basic types of piriformis-sciatic nerve varitions are described in the literature and their distribution among the human population are presented in details.…”

Agenesis of the piriformis muscle: A case report with review of literature

“…However, Ikidag 8 presented a case with left flank pain but with contralateral piriformis agenesis. Brenner et al 7 reported in a cadaveric dissection case, piriformis agenesis, an ipsilateral common gluteal artery and an absent inferior gemellus muscle. In our case, the patient had progressively worsening low back pain radiating to both legs without neurological deficits on examination.…”

“…Following an extensive literature review, only a handful of case reports on the absence or agenesis of the piriformis muscle are documented. 5,7,8 Only two cases have been reported in living human subjects. 5,8 Because of the rarity in incidence, not much is known about the presenting symptoms, clinical findings and sequelae of piriform agenesis.…”

“…It is also an important reference for the surgeon performing tendon release of various pelvic muscles and the posterior surgical approach in total hip arthroplasty. 7 It can be postulated that the variation in the anatomy of such an important landmark definitely increases the risk of complications if the surgeon or interventionist is not aware.…”

On the Function of Piriformis Muscle in Relation to Piriformis Syndrome

“…Important neurovascular structures pass through infrapiriform foramen, including sciatic nerve [2]. In literature, case examples with variations of no or two piriformis have been reported [8][9][10][11].…”