Ⅰ. INTRODUCTION

Vascular malformation are congenital anomalies of the vascular system characterized by abnormally formed but mature blood vessels that are present at birth and grow proportionately with the patient^{1, 2}. They do not undergo spontaneous regression and may remain unnoticed until they enlarge or become symptomatic^{1, 3}. The head and neck region is a common site for these lesions, reflecting the rich and complex vascular network in this area². Within the oral cavity vascular malformations are less frequently encountered, and lesions confined to the buccal mucosa are particularly uncommon. This relative rarity can contribute to diagnostic uncertainty and delay in referral. The current International Society for the Study of Vascular Anomalies (ISSVA) classification distinguishes vascular malformations from vascular tumors and categorizes malformations according to the predominant vessel type and flow characteristics⁴. Vascular malformations are classified based on the predominant vessels involved into capillary, venous, lymphatic, and arteriovenous malformations and further categorized as high-flow or low-flow depending on the rate of blood flow through the lesion⁵. Although these lesions may share overlapping features such as discoloration, swelling, and soft tissue distortion, the underlying hemodynamics and biological behavior differ substantially among subtypes^{6, 7}. Capillary malformations tend to grow slowly and have a favorable prognosis. Lymphatic malformations can be associated with significant morbidity, sometimes even mortality, owing to their complex management challenges⁸. Venous malformations generally have a good prognosis but may cause problems such as pain, swelling and functional impairment⁹. Arteriovenous malformation shows the worst prognosis due to their high-flow nature and risk of severe complications¹. Delayed or incorrect diagnosis of vascular malformations often leads to complications such as thrombosis, hemorrhage, increased susceptibility to infection, and tissue necrosis, which may cause irreversible damage. Therefore, accurate clinical diagnosis is essential and requires careful clinical examination and appropriate imaging studies to distinguish them from other vascular anomalies or soft tissue lesions. Venous malformations typically manifest as soft, compressible, bluish lesions that may expand with dependency or Valsalva maneuver^{1, 10}. In the buccal mucosa, they can interfere with mastication, speech, and oral hygiene, and may cause bleeding or cosmetic concerns¹¹. Because their appearance can mimic other entities, such as hemangiomas, mucoceles, varices, or minor salivary gland lesions, careful differentiation is essential. Doppler ultrasonography and magnetic resonance imaging are particularly useful to confirm the low-flow nature, define lesion boundaries, and assess involvement of adjacent structures¹. This case report describes a low-flow venous malformation arising in the buccal mucosa and discusses diagnostic and therapeutic considerations, aiming to provide clinicians with a practical framework for managing similar lesions in the head and neck region.

Ⅱ. CASE PRESENTATION

A 45-year-old woman presented with a mass in the right buccal mucosa, first noticed one year ago. She had been diagnosed with a benign tumor at an otolaryngology clinic and followed periodically. Four days before presentation, she developed pain and swelling in the area and visited our hospital. She has no significant past medical history but was taking medication for hypercholesterolemia without aspirin use. No remarkable laboratory findings or family history were noted, and she reported no relevant dental history. Clinical examination revealed a blue-colored lesion in the buccal mucosa without ulceration or disruption of the overlying oral mucosa (Fig. 1). The lesion was easily compressible, with no change in color upon compression. Computed tomography demonstrated a 1.6 x 2.3 cm well-defined, mildly enhancing lesion in the right buccal space with internal calcification suggestive of venous malformation, likely accompanied by secondary thrombosis and phlebolith formation (Fig. 2). Magnetic resonance imaging showed 2.0 x 1.5 x 1.8 cm well-defined lesion with low T1 and high T2 signal intensity, mild enhancement, and no diffusion restriction, further supporting diagnosis of venous malformation with calcification (Fig. 3). Ultrasonography revealed a hypoechoic compressible lesion with internal echoes consistent with phleboliths (Fig. 4). Under the diagnosis of low-flow venous malformation, sclerotherapy was planned as a single session, with subsequent treatment to be determined based on therapeutic outcomes. However, the patient declined the interventions due to fear of injections, and the lesion remained unchanged during two months following initial presentation. Therefore, periodic follow-up was scheduled, reserving sclerotherapy for lesion progression or complication prevention. Sixteen months later, the patient returned complaining of a slight increase in lesion size and discomfort due to its solid consistency, which felt like hardened candy. Though the patient reported changes in the lesion, clinical examination revealed no significant difference from the previous visit, and regular follow-up was recommended without further intervention (Fig. 5).

Ⅲ. Discussion

Vascular malformations are common in the head and neck region, with venous malformations occurring less frequently than capillary malformations. Differentiating between these entities is critical for accurate diagnosis and optimal treatment selection. While both commonly affect the cheeks and lips¹², their age distribution differs. Venous malformations predominantly occur in children aged 0-4 years without sex predilection and decrease with age, whereas capillary malformations are more common in females aged 0– 4, 30-34, and 50-59 years⁹. The diagnosis of venous malformation at age 45, as in this case, seems to be uncommon, as is the anatomical location in the buccal mucosa. Literature suggest that buccal mucosa venous malformations are typically diagnosed between ages 20 and 60, later than lesions in other regions. Given their congenital nature, the reason for late detection remains unclear. It is hypothesized that lesions may be initially small and asymptomatic but gradually enlarge over time¹³. However, this hypothesis applies to venous malformations at all sites and does not fully explain the site-specific late presentation in the buccal mucosa. We suspect that the lesion was originally present but unnoticed by the patient due to the thick nature and complex anatomy of the buccal mucosa, which contains facial muscle, parotid gland, and submucosa, compared to relatively superficial lip and ventral surface of tongue. Symptom onset may relate to injurious stimuli such as inflammation or blockage of venous drainage, leading to enlargement and engorgement of the venous malformation. Regardless of the exact pathogenesis, age at diagnosis should not be overemphasized in diagnosing the lesion. Thus, low-flow venous malformations should be considered when clinical features include a bluish-colored lesion, thrombosis, and/or phleboliths, especially in older patients with buccal mucosa lesions.

Treatment strategies for low-flow venous malformations include sclerotherapy, surgical excision, combined sclerotherapy and surgical excision, laser therapy, and conservative management with compression¹⁴. Among these, sclerotherapy is the first-line treatment due to its minimally invasive nature, convenience, and suitability for access for head and neck region^{15, 16}. However, sclerotherapy has limitations, including pain, nerve injury, recurrence, and allergic reactions, and the need for repeated procedures. Therefore, various drugs for sclerotherapy are continuously investigated for effectiveness and safety in the treatment of VMs in the head and neck region¹⁷. When sclerotherapy is contraindicated or refused, conservative therapy with or without compression may be considered. However, the use of compression therapy is often impractical for intraoral lesions, as it typically requires custom-made devices such as denture- like appliances or intraoral splints, unlike the readily available methods (e.g., stockings) used for extremity lesions ¹³. Conservative pharmacotherapy, such as the use of phlebotonic agents or and NSAIDs, may be considered for symptomatic relief, but is not indicated for asymptomatic lesions and may be limited by patient comorbidities¹³. In the absence of symptoms and given the limitations of other non-surgical options, periodic follow-up without active intervention constitutes a reasonable management option. Patients must be thoroughly educated on symptoms that warrant immediate attention. They should be advised to seek immediate evaluation if they notice acute pain, swelling/ edema, hemorrhage, suspicion of infection, or rapid growth of the lesion. Through this report, we suggest that periodic follow-up without active intervention can be a reasonable option for asymptomatic, low-flow venous malformations when serious complications are absent and other active treatment modalities are not feasible.