Abstract
Arteriovenous malformations (AVMs) of the temporalis muscle are an extremely rare subgroup of head and neck AVMs. The authors report two cases presenting with temporal fossa tumor-like lesions. MRI demonstrated enlargement of the temporalis muscle with hypointensity on T1, hyperintensity on T2 and moderate contrast enhancement. Angiography shows slow arteriovenous shunting with a dense capillary blush of the entire muscle before draining into facial veins. The arterial supply is characteristic of being restricted to the temporalis muscle.
In the authors’ experience, head and neck arteriovenous malformations (AVMs) are relatively rare compared with brain arteriovenous malformations (BAVMs). A review of the institution’s vascular malformation database from June 1984 to April 2007, revealed approximately 1090 BAVMs compared with about 70 cases with scalp or facial AVMs. Of these, only two were localized exclusively in the temporalis muscle. Scalp AVMs are localized primarily in the subcutaneous tissue, but involvement of the underlying muscle can also occur and was reported in up to 50% in F isher-Jeffes et al. . Lesions that are only localized in the temporalis muscle are extremely rare, only two cases have been reported . Intramuscular AVMs more commonly occur in the extremities, particularly the lower limbs . The authors describe the imaging characteristics of the two cases with an intramuscular AVM of the temporalis muscle and discuss how an accurate diagnosis may impact on the management of these lesions.
Case reports
Case 1
A 20-year-old woman, presented with a 6-month history of progressive left temporal swelling that fluctuated in size and was aggravated by positioning . The lesion was not known to be present prior to that time nor did she have any cutaneous lesions. There was no history of trauma. Computed tomography (CT) and magnetic resonance imaging (MRI) revealed tumor-like enlargement of the left temporalis muscle, which had slight low-signal intensity compared with other muscles on T1 and high signal intensity on T2WI with moderate contrast enhancement ( Fig. 1 ). Few small flow-void structures within the muscle were observed.
A neoplasm was suspected and surgical resection of the lesion was planned. A preoperative angiogram revealed a hypervascular lesion supplied by branches of the left superficial temporal artery (STA) and left posterior deep temporal artery with slow-flow arteriovenous shunting in the left temporalis muscle. Mild ectasia of the arterial feeders was noted with dense capillary staining of the entire muscle. Embolization using a 16% concentration of N-butyl cyanoacrylate (NBCA) mixed with 84% lipiodol as well as 250–350 μm polyvinyl alcohol (PVA) particles was carried out to devascularize the lesion.
Surgical removal of the lesion was performed the next day with a longitudinal incision along the temporal hairline overlying the lesion. The temporal scalp was reflected followed by resection of the lesion, which included the temporoparietal fascia and a portion of the temporalis muscle. Hemostasis was easily obtained with a bipolar cautery and the wound was closed over a Jackson-Pratt drain, which was later removed. Surgical pathology revealed large vessels with features of arteries and veins often in the same section. There was significant cellular intimal hyperplasia in many of the sections with multiple areas containing occlusive masses of foreign (Gelfoam-like) material in the lumen and focal mild chronic inflammation. The surrounding skeletal muscle and interstitium showed variable sized areas of smaller vessels without features of neoplastic disease. The appearance was that of an arteriovenous malformation with evidence of recent embolization.
Case 2
A 19-year-old man presented with a mass at the left temporal region which had been progressively enlarging for about 2 years. The lesion had enlarged for about 6 months and then appeared to change more slowly in size. There was no pain or skin change. There was no history of trauma. Physical examination revealed a non-pulsatile compressible mass at the left temporal region. CT and MRI revealed marked diffuse enlargement of the left temporalis muscle with isosignal on T1 and hypersignal on T2 tissue characteristics compared with the surrounding muscle, with moderate contrast enhancement ( Fig. 2 ). Few flow-void structures were noted within the muscle.
A preoperative angiogram revealed a large hypervascular lesion supplied by branches of the left STA, left anterior and posterior deep temporal arteries with capillary blush involving the entire left temporalis muscle. There was slow-flow arteriovenous shunting into the surrounding facial veins. Transarterial superselective embolization was carried out with 40% NBCA and 60% lipiodol mixture. Surgical removal was carried out the next day through a left temporal hairline incision. The lesion, along with the left temporoparietal fascia and most of the left temporalis muscle were resected with minimal blood loss. Pathology revealed large artery-like vascular channels with adjacent areas of much thinner, vein-like channels. An occasional vessel showed what looked like a combination of the two with a part looking like an artery and the rest like a vein. There were small aggregates of compact masses of endothelial-looking cells scattered within the vessels and subcutaneous tissues. A few clusters of striated muscle fibers were also seen. The findings were compatible with an arteriovenous malformation. There was no evidence of neoplastic disease.
Discussion
Vascular malformations of the head and neck are congenital lesions resulting from developmental errors of angiogenesis and vasculogenesis . As M ulliken & G lowacki reported in 1982 , they can be differentiated from hemangiomas by clinical history and imaging characteristics, the latter being a tumor and having the potential of growth and regression . Vascular malformations, due to their congenital nature, can be present since birth, but they usually present clinically later in life. The lesions grow with the child and can exacerbate with trauma or hormonal changes . On histopathology, hemangiomas are characterized by the presence of increased mitotic activity with a laminated appearance of the basement membrane, while vascular malformations have normal endothelial mitotic activity . They can be categorized according to the channel anomaly into arterial, capillary, venous, lymphatic and combined groups, the imaging characteristics of each type of classic vascular lesion are summarized in Table 1 .
| Lesion | MRI findings | Angiographic findings |
|---|---|---|
| AVM | Flow-voids | Rapid AV shunting |
| No focal mass, possible soft tissue thickening | Enlarged arterial feeders, multiple collateral supply | |
| Ectatic draining veins | ||
| Capillary | Slow-flow | Capillary blush |
| No flow-voids | Slightly early AV shunting/no AV shunting | |
| Small dilated spaces | No enlargement of the arterial feeders/veins | |
| Venous malformation | Slow-flow, some enhancement | No AV shunting |
| No flow-voids, phleboliths | No arterial feeders | |
| Dilated spaces, isointense to muscle on T1/hyperintense on T2 | Possible visualization of ectatic venous spaces in late venous phase | |
| Lymphatic malformation | No flow, no enhancement | Normal angiogram |
| No flow-voids | ||
| Dilated spaces | ||
| Hypointense to muscle on T1/hyperintense on T2 | ||
| Hemangiomas (proliferative) | Focal mass, enhancement | Hypervascular mass with AV shunting |
| Few flow-voids | Slightly enlarged feeding arteries and draining veins | |
| Isointense to muscle on T1/hyperintense on T2 | ||
| Hemangiomas (involutive) | Areas of high signal on T1 | |
| Less enhancement than proliferative stage | ||
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