Masseter Muscle Hernia: Rare Case Report of Surgical Management via Preauricular Approach and Mesh

Summary:

Masseter muscle hernia (MMH) is an exceptionally rare condition characterized by muscle protrusion through a weakened fascia, with only 4 cases previously reported worldwide. Typically presenting as an asymptomatic tumor at the mandibular angle, MMH becomes more evident during mastication. Diagnosis relies on dynamic imaging, such as ultrasound, whereas treatment remains undefined due to its rarity. We report a novel case of MMH managed surgically with a preauricular approach and mesh reinforcement. A 35-year-old woman presented with a 6-month history of a painful, ovoid tumor (25 × 18 mm) at the right mandibular angle, exacerbated by chewing. Physical examination revealed a semisoft mass that hardened and enlarged with teeth clenching, reducing in size at rest. Dynamic ultrasound confirmed MMH by demonstrating muscle protrusion during contraction. Surgical intervention involved a preauricular approach, dissection of the superficial musculoaponeurotic system, primary closure of a 1 × 1.8 cm fascial defect, and polypropylene mesh reinforcement. The patient recovered well, with no recurrence at 12-week follow-up. This case highlighted MMH as a rare entity, predominantly affecting young women, with pain distinguishing it from prior asymptomatic reports. Dynamic ultrasound proved effective for diagnosis, and surgical repair with mesh reinforcement offered a successful outcome. This approach may serve as a viable option for managing similar cases, expanding the limited treatment repertoire for this uncommon condition.

Muscle hernias are an infrequent pathology, usually located in the lower extremities, particularly in the tibialis anterior muscle.¹ They occur due to an alteration or weakness of the muscle fascia that allows protrusion of the underlying muscle tissue.² However, masseter muscle hernia (MMH) is an extremely rare clinical finding. To date, only 4 cases have been reported in the medical literature.^2–5

Diagnosing MMH is difficult due to its rarity and resemblance to cysts, lipomas, parotid tumors, and other masses. Dynamic ultrasound is the preferred imaging modality, enabling real-time visualization of muscle herniation during contraction,⁶ whereas magnetic resonance imaging (MRI) may help rule out structural abnormalities in select cases. Given the few reported cases, MMH etiology remains uncertain; proposed causes include congenital weakness, trauma, or fascial degeneration linked to bruxism or excessive chewing.² We present the case of a female patient with an MMH who was treated surgically with primary closure of the defect and polypropylene mesh reinforcement.

CASE STUDY

Clinical Presentation

A 35-year-old woman with no significant medical history presented to the outpatient clinic with a tumor at the angle of the mandible, which had been evolving for 6 months. She noted mild pain with chewing and occasional paresthesia. On examination, a well-defined, ovoid, semisoft mass (25 × 18 mm) was noted, which became more prominent with clenching and reduced at rest (Fig. 1). It was mildly tender on palpation (Fig. 2). Intraoral examination was normal, with no signs of bruxism.

Fig. 1.

Dynamic ultrasound demonstrating masseter muscle contraction with visible protrusion consistent with a masseteric hernia.

Fig. 2.

Preoperative photograph without masticatory maneuver, showing a subtle soft tissue prominence at the right mandibular angle at rest.

Dynamic Muscle Ultrasonography

Based on the clinical findings, dynamic muscle ultrasonography was performed. The hernia protruded more during sustained contraction of the masseter when the patient clenched her teeth, decreased at rest, and nearly disappeared when the mouth was opened. These findings confirmed the diagnosis of MMH at the level of the right mandibular angle.

The benign nature of the defect and the available surgical options were explained to the patient. She chose to undergo surgery due to pain while chewing and aesthetic concerns.

Surgical Technique

A preauricular incision was marked with a 2-cm retroauricular extension. Local infiltration was performed using a 0.1% lidocaine with epinephrine solution. Subcutaneous dissection was initiated and transitioned to a deep sub-superficial musculoaponeurotic system (SMAS) plane approximately 2 cm posterior to the hernia. The preparotid and masseteric fascia were identified, dissected, and carefully elevated to protect the buccal branch of the facial nerve and expose the muscle fibers. A 1 × 1.8 cm fascial defect was identified, with elongated muscle fibers herniating through it. The hernia was manually reduced, and the fascial defect was closed using horizontal mattress sutures (polydioxanone suture 4-0). A polypropylene mesh (1.5 × 2 cm) was then placed over this primary closure, in direct contact with the underlying masseter muscle but carefully positioned to avoid contact with any facial nerve branches. The mesh was secured to the surrounding fascia to reinforce the repair (Fig. 3). Hemostasis was confirmed, and layered closure was performed.

Fig. 3.

Intraoperative view showing the repaired fascial defect closed with horizontal mattress sutures (PDS 4-0), reinforced with a 1.5 × 2 cm polypropylene mesh secured to the fascia. PDS, polydioxanone suture.

The patient had an uneventful recovery with appropriate wound healing and no motor or sensory deficits. At 12 weeks of postoperative follow-up, no evidence of recurrence was observed (Fig. 4).

Fig. 4.

Postoperative photograph at 3-month follow-up during masticatory maneuver, showing no visible masseteric hernia.

DISCUSSION

MMHs are rare, with only a few cases documented in the literature.^2–5 The first reported case, by Römer³ in 1966, described a female patient with a cherry-sized mass that became prominent during clenching. Surgical exploration under local anesthesia via a submaxillary approach revealed herniated muscle fibers, which were repaired with deep sutures to the fascia, resulting in good functional and aesthetic outcomes at 6 months.³

All 5 reported cases, including ours, involved young women aged 14–35 years, with our patient being the oldest. Presentation was consistent—a mass that enlarged with clenching and resolved at rest—though ours was the only case with pain during mastication and palpation.

Only 1 case suggested a likely cause—trauma from a severe bite—implying that intense clenching may rupture the fascia.⁴ Other possible mechanisms include sudden fascial weakening or overstretching during wide mouth opening, though no cases have reported connective tissue disorders such as Ehlers–Danlos syndrome.^7,8 The masseter muscle plays a key role in jaw movement, generating rotational and translational forces. Chronic clenching from bruxism or gum chewing may cause localized stress and hypertrophy, but in the absence of clear triggers, MMH pathogenesis remains unclear.

Dynamic ultrasound is the preferred imaging for MMH, as it allows real-time visualization of herniation during muscle contraction, with reduced echogenicity observed in the affected tissues. Unlike MRI, which may need multiple scans at rest and during contraction, ultrasound is quicker, cost-effective, and confirmed the diagnosis in a single session in our case.⁵

Computed tomography ruled out structural abnormalities, making MRI unnecessary, whereas biopsy confirmed the presence of herniated muscle fibers. Differential diagnoses include cysts, lipomas, parotid tumors, masseter hypertrophy, hemangiomas, and various jaw lesions.⁵ Additional considerations include vascular malformations or neoplasms, parotid and facial nerve tumors, and, in trauma-related cases, retained hematomas or muscle tears. Of the 5 MMH cases, 4 underwent surgery following standard hernia repair principles; 3, including ours, used an external approach. We used a preauricular incision with deep-plane SMAS dissection, fascial closure, and mesh reinforcement to reduce recurrence risk. Although synthetic mesh carries potential risks—such as fibrosis, adhesions, infection, or foreign body reaction—none were observed in our case during the 12-week follow-up.

Of the 5 MMH cases, 4 underwent surgical repair; 3, including ours, used an external approach. We used a preauricular incision with deep-plane SMAS dissection, fascial closure, and mesh reinforcement, a technique similar to that used in abdominal hernias. Although no complications were observed at 12 weeks, longer follow-up is needed to assess potential mesh-related adhesions or fibrosis. Avoiding nerve injury is a key intraoperative challenge. Future research may explore alternatives such as acellular dermal matrices to reduce adhesion risk.

CONCLUSIONS

MMH is a rare condition seen in young women. Dynamic ultrasound aids in diagnosis, and treatment follows standard hernia repair principles. Botulinum toxin may help in hypertrophy cases. Our preauricular approach with SMAS dissection and mesh reinforcement is a viable option.

DISCLOSURE

The authors have no financial interest to declare in relation to the content of this article.

PATIENT CONSENT

The patient gave written informed consent for sharing her case details and images. Every precaution was taken to safeguard her privacy and confidentiality, ensuring her identity remains undisclosed in this report.