Intramuscular Venous Malformation Associated with Muscle Herniation of the Left Masseter Muscle in a 12-Year-Old Boy

Introduction

A muscle herniation is defined as a focal protrusion of the muscle tissue through a defect in its fascia, which could be congenital or acquired secondary to trauma. It appears as a soft nodule that increases in volume during exercise and disappears with rest. Masseter muscle herniation is a very rare condition and to our knowledge only a few cases have been reported in the literature. It should be suspected when a patient has a mandibular angle swelling that appears with teeth clenching and disappears when the mouth is open. Dynamic ultrasonography is the imaging modality of choice for diagnosis [1].

The most recent International Society for the Study of Vascular Anomalies (ISSVA) classification classified vascular anomalies primarily into 2 types: 1) “Vascular tumors” with proliferative changes of the vascular endothelial cells which includes, and 2) vascular malformations that are vascular structural abnormalities without proliferative changes of the vascular endothelial cells [2]. Venous malformation (VM) is the most common type of low-flow vascular lesion, accounting for two-thirds of congenital vascular malformations (CVMs) and are predominantly sporadic and unifocal lesions; however, 1% are multifocal [3].

VM, previously known as cavernous hemangioma, is the most common type of CVM, with 1 to 2 per 10000 incidence and 1% prevalence [4]. In this report we use the terms cavernous hemangioma and VM lesions interchangeably.

Intramuscular venous malformation (IMVM) are rare entities that mostly occur in the head and neck, as well as extremities, and tend to be localized to a single muscle or a muscle group. Two-thirds of IMVM are noted at birth, and the remainder manifest in childhood and adolescence. IMVM are frequently asymptomatic and can be missed [5].

Less than 1% of vasoformative tumors occur in the skeletal muscles, and 15% arise in the head and neck. The masseter muscle is the most frequent site, with a typical clinical presentation and medical imaging features that allow it to be easily distinguished from other abnormalities [6]. A wide variety of tumors can be confused with IMVM, such as salivary neoplasms, cysts, lymphangiomas, rhabdomyosarcomas, masseter hypertrophy, and schwannomas [7]. The wide variety of vascular and non-vascular lesions pose a diagnostic challenge, as in the current case.

This report presents the case of a 12-year-old boy with an IMVM of the left masseter muscle coexisting with masseter muscle hernia. To the best of our knowledge, this coexistence has not been reported before in the masseter muscle, and it has rarely been reported in other muscles.

Case Report

A 12-year-old presented with a long-standing focal swelling in the left cheek, particularly noticeable during eating. Living in a rural area, the patient faced challenges accessing healthcare due to distance, limited transportation, and scarce medical facilities, leading to a delay in seeking medical advice. As time passed, the pain worsened, occasionally hindering eating activities. Eventually, the severity of the discomfort prompted the patient to seek medical attention. Apart from the cheek issue, the patient had no other medical concerns. Clinical examination revealed no abnormalities in other body systems, with no observable focal swelling or skin discoloration. However, focused examination of the affected area revealed a soft swelling in the left cheek, exacerbated by teeth clenching and alleviated at rest (Figure 1A, 1B).

Lateral X-ray revealed rounded calcification over the left mandibular region (Figure 2). Ultrasonography revealed a bulky left masseter muscle compared to the right, with mild heterogeneous structure, and evidence of 2 rounded calcified foci with distal acoustic shadowing (Figure 3A, 3B). Ultrasound Doppler found scattered focal color flow, with dilated blood vessels with slow venous flow and without detectable arterial spectral waveform. This, with the absence of associated soft tissue and presence of calcifications on X-ray, is radiologically diagnostic for VM (Figures 2, 3C, 3D). Ultrasonography with clenching of teeth revealed a superficial facial defect overlying the left masseter muscle with focal muscular herniation externally and was relieved by stopping clenching of teeth (Figure 3E, 3F).

The clinical and radiological findings led to diagnosis of left masseteric muscle hernia with coexistent IMVM. Surgery was performed to alleviate the pain, with excision of the left masseteric muscle lesion, the hernial defect was repaired, and a specimen was sent for histopathology.

Histopathology results showed left masseteric IMVM (Figure 4), and the patient was discharged without any immediate postoperative complications. At 6-month follow-up, the patient was completely free of any complications.

Discussion

This case report highlights that masseter hernias and IMVMs should be considered in the differential diagnosis of any masseter lesion and the importance of imaging in reaching the appropriate diagnosis. Muscle hernias are relatively rare occurrences characterized by the protrusion of muscle through a defect in its fascia. While they can occur in any part of the body where muscles are present, most are located in the extremities, with the tibialis anterior being the site most often reported in the literature. Excessive physical activity and trauma are proposed to be the main causes of muscle hernia. Congenital muscle hernias, on the other hand, occur as a result of inherent weaknesses in the muscle fascia, predisposing individuals to herniation with increased physical exertion [1,8]. Masseter muscle hernias, specifically, are particularly uncommon and to our knowledge only a few cases have been reported in the literature, all of them diagnosed in children, which supports the supposed congenital etiology.

Diagnosis of muscle hernias typically involves identifying focal protrusions of the affected muscle, which may become more prominent during muscle contraction and diminish upon relaxation. Most muscle hernias are asymptomatic and remain undiagnosed. However, over time with increasing muscular exercise, pain can develop either secondary to transient ischemia on the herniated muscle and/or increased pressure created on the overlying soft tissue [8]. In our case the presence of the protrusion on the face made the lesion very noticeable early in childhood. The lesion was symptomatic at the beginning, and the pain developed gradually.

Muscular hernia can be evaluated by dynamic ultrasound, a valuable diagnostic tool capable of visualizing the affected area during both contraction and relaxation of the involved muscle – the masseter muscle in our case. While clinical examination and ultrasound are typically enough for diagnosing muscle hernias [1,9], MRI can provide valuable additional information, especially in complex cases or when there is uncertainty about the diagnosis. MRI offers detailed imaging of soft tissues and help assess the extent of the herniation and any associated soft tissue injuries or complications [10].

Despite their rarity, understanding and diagnosing muscle hernias, including those involving the masseter muscle, is essential for appropriate management and treatment planning.

Venous malformation refers to the abnormal growth and development of a single type of vessel or a combination of vessels within the venous system. This condition is characterized by the presence of malformed veins, which may vary in size and appearance. Venous malformations can occur anywhere in the body and may manifest as soft, compressible masses or lesions beneath the skin. The underlying cause of venous malformations is often attributed to errors in embryonic development, leading to the improper formation of veins and their associated structures. While venous malformations are typically benign, they can cause discomfort, pain, or complications such as thrombosis or bleeding, depending on their location and size. IMVM can be difficult to diagnose due to delayed presentation, deep intramuscular location, and vague clinical manifestations [11]. In the head and neck, the masseter muscle is the most frequently involved muscle, followed by the trapezius, periorbital, sternomastoid, and temporalis muscles. Tongue, extraocular, and posterior neck muscles are the least frequently affected [12]. Liston first reported intramuscular hemangiomas (IMHs) in 1843 [13]. In this report, we documented an extremely rare IMVM in the masseter muscle of a 12-year-old boy who presented with a mass in the left mandible region.

X-ray and MRI are the typical imaging methods used to diagnose IMHs. X-ray shows calcified phleboliths in 25% of IMHs [14]. VMs mostly undergo a continuous cycle of spontaneous thrombosis and thrombolysis, and persistent thrombi may calcify, resulting in phleboliths formation, which is pathognomonic for VM on plain X-ray [3]. In our case, X-ray found rounded calcification over the left mandibular region, which was the key to diagnosis. Melman and Johnson reported that phleboliths on X-ray are specific findings for cavernous hemangioma [15]. In our patient, ultrasonography found a mixed echogenicity lesion in the left masseter muscle with a rounded focus of calcification and calcification-related acoustic shadowing. Ultrasound Doppler found dilated blood vessels with venous flow. These findings are similar to those of a previous case report [16].

Melman and Johnson reported that the typical presentation of cavernous IMH is an enlarging soft-tissue mass without cutaneous changes, but it can be locally destructive, and most do not undergo spontaneous regression; surgical excision is the definitive treatment [15]. Our patient underwent surgical excision of the left masseter IMVM, the hernial defect was repaired, and the patient completely recovered.

The 2020 WHO classification of soft tissue tumors reported that histopathology is the criterion standard for diagnosis and grading of soft tissue lesions, but radiology-pathology confirmation is crucial to avoid misdiagnosis [17]. In our patient, the diagnosis of VM was confirmed by histopathology findings of typical VM. The goal of treatment should be to cure the VM using 1 or more of the available various methods, including conservative treatment, sclerotherapy, laser therapy, and surgery [18]. However, the results of non-surgical methods of treatment such as cryotherapy, corticosteroids, sclerosant injection, isolated embolization, arterial ligature, and radiation therapy are controversial [19]. In our case, surgery was feasible and achieved good results, consistent with the results of surgery in a previous case [19].

The coexistence of IMVM and muscle hernia is extremely rare. We hypothesize that individuals with congenital muscle hernias may have an increased predisposition to the development of venous malformations due to underlying structural weaknesses in connective tissues. The inherent weaknesses in the muscle fascia associated with congenital muscle hernias could potentially extend to surrounding vascular structures, including veins. This structural vulnerability may create a conducive environment for abnormal growth and development of venous vessels, leading to the formation of venous malformations. However, the absence of literature on the coexistence of muscle hernia and venous malformation could be related to the fact that most reported cases of muscle hernia were traumatic, and the coexistence could involve unrecognized congenital factors. Future research exploring potential shared genetic predispositions or common pathways in connective tissue and vascular development may shed light on their possible association. Collaborative studies between specialists in radiology, genetics, and vascular medicine may provide valuable insights into the underlying mechanisms and clinical implications of their coexistence. Furthermore, the management of muscle hernias complicated by AVMs poses unique therapeutic challenges. While surgical repair of the muscle hernia may alleviate symptoms and improve functional outcomes, the presence of an AVM necessitates careful preoperative planning to mitigate the risk of intraoperative hemorrhage and postoperative complications. Multidisciplinary collaboration involving vascular surgeons, orthopedic surgeons, and radiologists is often essential for optimal results.

Conclusions

To the best of our knowledge, this is the first report of the coexistence of these 2 rare pathologies within the masseter muscle: muscle hernia and IMVM. This occurrence may stem from congenital muscular weakness and structural disruption and may be related to shared genetic defects, which require further collaborative studies to explore the underlying pathophysiology. Comprehensive diagnosis can be achieved through a combination of clinical examination, X-ray, and ultrasound assessments.