Phlebolith in arteriovenous malformation in buccal fat pad masquerading sialolith: A rare case report.

Arteriovenous malformations (AVMs) are rare vascular lesion in the buccal fat pad (BFP). One of the important complications associated with these lesions is phlebolith formation within it. To the best of authors' knowledge, there is no medical literature on AVM with phlebolith formation in BFP till date. The present case is a 12-year-old boy who presented with a swelling in the right side of the face, clinically diagnosed to be sialocele with sialolith. Excision of the mass was done, and histopathology revealed AVM with the formation of phlebolith. This rare entity needs to be kept in mind while evaluating a case of calcification in BFP. The first case of AVM with phlebolith formation in BFP is reported here along with brief review of literature.

Introduction

Calcifications found on routine radiographs of the orofacial region may turn out to be an interesting diagnosis. Although in most of the cases radiopacities may be sialoliths, other differential diagnoses must not be exempted, such as calcified lymph nodes, calcification following trauma, calcifying fibrous tumor, dystrophic ossification, and phlebolith.

Vascular tumors are the most common benign tumors of the head and neck in infancy and childhood. Vascular anomalies of the head and neck were divided into two categories including hemangiomas and vascular malformations.[1] Arteriovenous malformations (AVMs) are a complex network of intercommunicating arterial and venous structures.[2] Changes in blood flow dynamics within dilated vascular spaces of AVM may result in phlebolith formation.[1]

Buccal fat pad (BFP) is a mass composed of adipose tissue covered with a thin capsule and is located in the buccal space, lateral to the buccinator muscle and deep to the zygomaticus major muscle.[3] BFP has a rich blood supply and any error in morphogenesis may give rise to AVM.[4]

After extensive search in various electronic databases, no report of AVM with phlebolithiasis in BFP has been found. Here, we report the first case of AVM with phlebolith in the BFP, not only because of its rarity but also due to its clinical simulation with sialolith.

Case Report

The patient was a 12-year-old boy presented to our dental out-patient department with the chief complaint of swelling in the right side of the face since last 1-year. Clinical examination revealed mild swelling in the right side of face which increased while crying or lying down but not during eating [Figure 1a]. On palpation, a unilobular, localized, movable mass, soft in consistency, was found along with a hard nodule within it in the right buccal space. There was neither any history of trauma nor any associated features of pain or fever. Patient was of normal built for his age and sex, and systemic examination was unremarkable. Our clinical diagnosis was sialolith with sialocele of the right parotid duct.

Figure 1

(a) Clinical photograph showing swelling in the right side of the face. (b) Sialographic image of right parotid showing normal parotid duct (arrow) and a separate spherical radio opaque mass (arrowhead). (c) Ultrasonographic image showing echogenic shadow (asterisk) within hypoechoic vascular lesion. (d) Magnetic resonance imaging (MRI) of the lesion. MRI revealed a hyperintense calcific speck within a hypointense vascular lesion

Fine needle aspiration yielded frank blood only with a reduction in the size of the swelling. Sialography of the right parotid showed normal parotid duct and gland but a spherical radiopaque mass was identified separately from Stensen's duct [Figure 1b].

Ultrasonography (USG) of the mass showed echogenic shadow, which was freely mobile along mandibular ramus within a hypoechoic vascular lesion. No dilated duct-like structure noted [Figure 1c].

To know the exact location and size of the mass and its relation to any vital structure, magnetic resonance imaging (MRI) was done which revealed well defined T1-weighted and T2-weighted mixed signal intensity lesion in right buccal region. T2-weighted MRI showed a hypointense calcific speck within a high signal intensity mass lesion [Figure 1d]. Angiography was advised but couldn’t be done as it was not available in our institution.

Based on clinical and radiographic examinations, preoperative diagnosis of a vascular lesion with phlebolith was made and an excisional biopsy was planned. Under general anesthesia and aseptic condition, surgery was done through intraoral approach [Figure 2]. Hemostasis was achieved and primary closure done. The specimen was sent for histopathological examination.

Figure 2

Intraoperative image of the lesion. Note the buccal fat pad with the hemangioma

Grossly the lesion was grayish yellow fibrofatty tissue measuring 5 cm × 1 cm × 0.5 cm with a separately sent phlebolith which was grayish white, hard, glistening globular measuring 0.7 cm in diameter [Figure 3a]. Microscopic examination showed fibro adipose tissue containing predominately intercommunicating dilated vascular channels of different calibers lined by a single layer of attenuated endothelial cells [Figure 3b]. The wall is irregularly thickened and collagenised without proper intimal layer or elastic lamina [Figure 3c]. These vascular spaces showed evidence of thrombosis with patchy dystrophic calcification and well-developed phlebolith [Figure 3d and f]. Few thick-walled vessels showing internal elastic lamina, which was highlighted by special stain are present along with the abnormal veins [Figure 3e]. The final diagnosis of arteriovenous hemangioma (AVH) with thrombosis and secondary calcification was made.

Figure 3

(a) Macroscopic image of phlebolith. (b) Microphotograph showing irregular dilated vascular spaces lined by flattened endothelial cells. One of the vascular space contain thrombus (arrow) (H and E, ×100). (c) Masson trichrome stain demonstrating irregularly thickened collagenized wall of the dilated vascular spaces (MT, ×100). (d) Higher magnification of a thrombus demonstrating dystrophic calcification (H and E, ×400). (e) Van Gieson's stain demonstrating internal elastic lamina in intralesional artery (arrow). Accompanying dilated vascular spaces lacks internal elastic lamina (arrowhead). (Van Gieson’s, ×100). (f) Histopathological view of phlebolith showing laminated concentric rings of calcification within a vessel wall with pressure atrophy of endothelium (H and E, ×100)

Postoperative period was uneventful, and postoperative USG revealed no residual mass lesion. Follow-up after 6 months showed no recurrence.

Discussion

Hemangiomas are considered as benign vascular tumors though controversies among the entities of malformation, reactive angiogenesis, and true neoplasm still persist. Morphologically it can be consisting predominantly of small capillary sized vessels, large cavernous type or mixed. AVMs are synonymous with arteriovenous hemangioma (AVH).[5] Demonstration of elastic lamina in wall of vessels is the most important criteria for differencing AVM from other hemangiomas.[4] In our case, Masson trichrome stain demonstrated the elastic lamina in some of the intralesional muscular arteries indicating this as AVM.

Phleboliths are calcified thrombi occurring in venules, veins, venous hemangiomas, cavernous hemangiomas or AVMs. Their formation is thought to be as a result of vascular stasis, which induces thrombus formation followed by organization of the thrombus and subsequent dystrophic calcification. The result is deposition end of a mixture of calcium carbonate and calcium phosphate with eventual stone formation.[6] They are usually laminated with a radiopaque center and concentric rings of calcification giving an “onion skinning like” appearance.[7] Phlebolith formation reported as a characteristic feature of vascular lesion was first described in the splenic vein.[8]

Arteriovenous malformations are true congenital vascular anomalies rather than tumors and are relatively uncommon lesions. Among hemangiomas occurring in head-neck region, cavernous type is most common. In a study of 35 cases of superficial AVH of oral cavity, only 4 cases of AVH of superficial buccal mucosa have been reported.[9] But AVM in the BFP has not yet been reported in English literature, to the best of authors’ knowledge.

Till date four cases of hemangioma in BFP have been reported. Deighan and Barton first reported a hemangioma case with phlebolithiasis in the BFP in 1956.[10] Only three other cases of hemangioma in the BFP have been reported of which one is cavernous, another capillary and in the other case type of hemangioma have not been specified.[111213]

Arteriovenous malformation is a complex network of intercommunicating arterial and venous structures. They need to be differentiated from other hemangiomas histologically. Their endothelial cell proliferation and turnover characteristics are normal in contrast to capillary hemangioma. They demonstrate a slow, steady growth pattern that commensurate with the growth of the child, and further, they also never involute. Complete excision of AVM is essential because incomplete excision results in recurrence.[5]

Angiography is the best diagnostic modality to confirm the diagnosis and establish the extent of disease. Accurate preoperative radiological assessment followed by histopathological confirmation is mandatory.