Arteriovenous malformations (AVMs) are abnormal connections between arteries and veins, bypassing the capillary system. They account for 2–6% of adolescent upper extremity vascular lesions, presenting diagnostic and treatment challenges due to their rarity, ambiguous imaging, potential for growth, mass effect, and recurrence ^[1]. AVMs, though congenital, may remain clinically silent until adolescence, often exacerbated by hormonal changes [2, 3]. We report a rare case of an extensive symptomatic AVM in the forearm of a 15-year-old girl, focusing on its clinical presentation, surgical management, and follow-up.

A 15-year-old right-handed female was referred to our tertiary care center with a 2-year history of progressively enlarging, painless mass in the right forearm, accompanied by tingling and numbness on the medial border and medial one-and-a-half digits. There was no history of trauma, fever, or weight loss. Physical examination revealed a localized, mobile, well-defined, non-tender, deep swelling measuring 4 × 4 × 12 cm, extending from the elbow to the distal forearm. No skin changes, bruit, or thrill, muscle wasting, fixity to underlying structures, or variable consistency was noted.(Fig. 1-3) Motor functions in the hand and forearm were normal, however sensory loss over the medial digits was present, with a positive Tinel’s sign and a negative Phalen’s test, suspecting nerve compression. Imaging studies, including Xray and MRI, revealed a well-defined, fusiform lesion located deep within the intramuscular plane of the dorsal forearm. The lesion measured 2.2 × 2.5 × 10.6 cm, appeared hypointense on T1-weighted images, and heterogeneously hyperintense on T2-weighted images, with no suppression on fat-saturated sequences. There were multiple blooming artifacts on GRE sequences, suggesting vascular channels. The lesion exerted a mass effect on the extensor digitorum and extensor digiti minimi muscles without evidence of invasion.(Fig. 1,2) It also compressed the ulnar neurovascular bundle, raising suspicion of schwannoma. Histopathological correlation was recommended to confirm the diagnosis.

Given the lesion’s extensive nature and proximity to the ulnar nerve, surgical excision was chosen as the optimal treatment approach. Under tourniquet control, meticulous dissection was performed to preserve the ulnar neurovascular bundle and other adjacent structures. Intraoperatively, the lesion exhibits a characteristic “nidus” pattern, which is a tangled network of blood vessels that are typical of AV malformations. The nidus was visible as a dense, reddish-pink irregular mass of vessels within the exposed tissues.(Fig. 4) No gross invasion of adjacent muscles or tendons was noted. Despite the vascular surgeon being on stand-by no major vessel involvement was observed and with the intact vasa nervosum on the opposite side, no re-anastomosis was performed and the excised end was coagulated and tied. (Fig. 5,6)Histopathology confirmed the diagnosis of an AVM, composed of dilated arteries, veins, and capillary proliferations.(Fig. 7) Post-operative recovery was uneventful, and the patient experienced full resolution of her symptoms. At the 1-year follow-up, clinical and radiological assessments revealed no recurrence of the AVM.

Pediatric vascular anomalies are broadly classified into hemangiomas and vascular malformations, based on clinical and histological characteristics [4, 5]. AVMs are considered high-flow vascular malformations due to the presence of direct arteriovenous shunting ^[6]. While AVMs are congenital, they may not become symptomatic until adolescence or later due to the influence of hormonal changes, as seen in this case [7, 8]. The patient’s AVM caused neural compression, leading to tingling and numbness, which are uncommon but reported symptoms in AVM presentations. [7, 9]. The classification of AVMs using systems such as the Schobinger staging, Yakes classification, and nidus morphology assists in diagnosis and management decisions. Our patient’s lesion was categorized as Type I in the Schobinger classification (quiescence) and Type I in nidus morphology, with minimal arterial feeders and venous outflow. This guided the decision to proceed with surgical excision rather than embolization, which was avoided due to the risk of nerve injury ^[2]. MRI remains the imaging modality of choice for evaluating AVMs, providing detailed information on the lesion’s extent, flow characteristics, and involvement of adjacent structures [2, 3, 9]. In our patient, the MRI findings indicated compression of the ulnar nerve, correlating with the clinical symptoms of sensory loss.(Fig. 2).  The recurrence rate of AVMs following surgical excision ranges from 47 to 76%, depending on the lesion’s size and complexity [1, 10]. In our case, complete excision was achieved without recurrence at 1 year. However, long-term follow-up is critical to monitor for recurrence, particularly in pediatric patients.

This case highlights the importance of considering AVMs in the differential diagnosis of forearm and hand swellings, particularly when accompanied by neurovascular symptoms. Surgical excision, when carefully performed, can lead to favorable outcomes with low recurrence rates. Given the high likelihood of recurrence, long-term clinical and radiological follow-up is essential for managing AVMs. Multidisciplinary care, involving radiologists, orthopedic surgeons, vascular surgeons, and pathologists, is crucial to optimize outcomes in complex cases like this.

This case highlights the importance of considering AVMs in the differential diagnosis of progressively enlarging, painless forearm masses in adolescents, particularly when associated with neurovascular symptoms, such as tingling and numbness. MRI plays a crucial role in diagnosis and surgical planning, while surgical excision remains the treatment of choice for symptomatic AVMs. A multidisciplinary approach is essential to optimize outcomes, and long-term follow-up is necessary due to the high risk of recurrence. Early diagnosis and appropriate intervention can prevent complications and improve patient quality of life.