I.Introduction

Caliber persistent artery (CPA) has been considered as a developmental vascular anomaly and found as large diameter artery immediately subjacent the surface epithelium.¹⁾ This phenomenon was first discovered in the gastrointestinal tract in 1962,²⁾ where it may cause fetal gastric hemorrhage. Caliber persistent labial artery (CPLA) in the submucosa of lip was described by Howell and Freedman in 1973.³⁾ Although CPA was often unrecognized and infrequently reported, it was known to be relatively common vascular anomaly.¹⁾

So far many cases of gastric CPA were reported, which showed the most dangerous form of gastrorrhagias; the overall lethality rate is 60.5%.^4-6) And the CPAs were occasionally found in sciatic artery and temporal artery.^7,8) A case of nose CPA was also reported.⁹⁾ Oral CPA usually occurs in the labial artery exhibiting soft tissue elevation of labial mucosa that can be bluish or normal in color, disappears when stretched, and pulsates on gentle palpation.¹⁾ Often the artery can be visualized through the stretched mucosa. CPLA usually occurs in an elderly population (average age = 58 years), is equally distributed between males and females, and twice as common in the upper lip than in the lower.^1,10-12)

CPA was usually asymptomatic with a few being associated with surface ulceration. When this lesion was clinically mistaken for a mucocele, fibroma or, other vascular lesion, and biopsied, brisk bleeding was encountered.^13,14) The ulcerated mucosa could be also misdiagnosed as squamous cell carcinoma.^1,15-18) Ultrasonography may help distinguish a CPLA from other vascular lesions of the lip such as an aneurysm, however, atypical cases of CPA with chronic ulcerations mimicking a cancer should undergo biopsy so that a malignant process is not missed.^19,20)

The present case of oral CPA occurred in the left retromolar buccal mucosa, exhibiting pinkish granular appearance mimicking hemangioma. It was asymptomatic but slowly growing for three years, and recently much irritable during mastication. A histological and immunohistochemical (IHC) study was performed to elucidate the architecture of CPA and its growth potential with the review of literature.

II.Case report

A 37 years old male patient showed a pinkish granular lesion in left retromolar buccal mucosa (Fig. 1A). This lesion was found about 3 years ago as a small pinkish spot, about 10 × 10 mm, but it was asymptomatic except slight irritation due to retromolar mucosa biting during mastication. He had a habit of heavy smoking, otherwise his general medical history was nonspecific. Recently the lesion increased in size up to 20 × 25 mm, and became hemorrhagic when the retromolar buccal mucosa was injured by deep molar biting. The pinkish granular lesion was partly ulcerated superficially but subsequently healed well, and showed slight pulsation on touch. The patient felt that the lesion was slowly growing and gradually extended to the adjacent buccal mucosa, therefore, he was afraid of the occurrence of oral cancer.

In the local clinic the lesion was primarily diagnosed as hemangioma, and still needed to be ruled out lymphangioma, biting purpura, oral cancer, etc. Therefore, a careful incisional biopsy was performed in the anterior margin of the retromolar buccal lesion, where biting wound was frequently happened. The removed specimen was referred to the Department of Oral Pathology, Gangneung- Wonju National University Dental Hospital (GWNUDH). The usage of biopsy specimens was approved by the institutional review board of GWNUDH (IRB 2015-07).

The specimen was fixed with 10% buffered formalin solution, routinely prepared for paraffin sections in 4 μm thickness, stained with hematoxylin and eosin (HE), and followed by the IHC stains using the triple sandwich indirect method described previously.²¹⁾ Particularly in order to know the architecture of vascular structure the serial microsections were made and their images were digitalized and analyzed under light microscope capture system (DP-70, Olympus, Japan).²²⁾

Histologically the lesion showed a tortuous artery (in the microsection the artery appeared as many arteries) localized at the submucosa area, and the size of artery was similar to the ordinary artery. But its intimal lining was thickened and its lumens were much narrowed (Fig. 1B). Many arterioles were also found in the vicinity of the artery, and they were occasionally branched and formed multiple vascular channels with the thick muscular wall (Fig. 1C). Some arteriole gradually grew into the adjacent muscle tissue, but capillary proliferation was sparsely observed (Fig. 1D). There appeared no features of arterio-venous malformation, usually characterized by the anastomosis between dilated arteries and veins. Therefore, with the differential diagnosis from hemangioma, lymphangioma, and arterio-venous malformation this lesion was diagnosed as retromolar buccal mucosa CPA.

The immunohistochemical study was subsequently performed using different antisera of proliferating cell nuclear antigen (PCNA*), α-smooth muscle actin (α-SMA^@), CD31*, vascular endothelial cell growth factor(VEGF*), basic fibroblast growth factor(b-FGF^#), capillary morphogenetic protein2 (CMG2^#), transforming growth factor β1 (TGF-β1^@), heat shock protein-70 (HSP-70*), 14-3-3, and transglutaminase 2 (TGase2*) (*Santa Cruz Biotech., USA; ^#NEOMARKERS, USA; ^@DAKO, Denmark).

In the immunochemistry α-SMA was positive for thick smooth muscle layer of arteries and arterioles, displaying the greatly tortuous architecture of CPA and the absence of vein vasculature (Fig. 2A-C). However, the immunoreaction of α-SMA was relatively weak throughout the artery,²³⁾ thereby, indicating that the artery was old and sclerosed. In some severely sclerosed artery α-SMA positive smooth muscle layer gradually disappeared and its lumen was shrunken with the thickening of intimal layer (Fig. 2C2). TGase 2 was weakly positive for the luminal surface of arterial intima. The TGase 2 reaction was partly positive on the endothelial cells (Fig. 2D). bFGF was consistently positive for the perivascular fibrous tissue, composed of collagenous connective tissue with a few capillaries (Fig. 1E). On the other hands, PCNA (Fig. 2E), VEGF, CD31 (data were not shown), CMG2 (Fig. 2F), TGF- β1 (Fig. 2G), HSP-70 (Fig. 2H), and 14-3-3 (Fig. 2I) were almost negative for the whole vascular lesion.

III.Discussion

CPA is supposed to be originated from the remnants of developmental vessels, of which circulation had been switched into other location during the embryonal morphogenesis. The existence of stapedial artery networks distributed in the mandibular and infra-orbital tissues may closely related to the high incidence of CPA in the perioral and facial areas. Actually the persistent strapedial artery is known to be a rare congenital anomaly that may present as a pulsatile middle ear mass found incidentally.²⁴⁾

CPA penetrates into submucosal tissue without division or reduction in arterial calibre. Intraorally, these abnormalities have been predominantly reported in the lip and rarely in the buccal vestibule²⁵⁾ and the eyelid.²⁶⁾ The present case of CPA in retromolar buccal mucosa was first reported in this study. As some CPLA cases were related to the lip biting habit and the lesion became dominant on touch. The present retromolar buccal mucosa CPA was also chronically irritated by biting and partly ulcerated.

Some typical small CPLA were not treated and abandoned after the clinical diagnosis, but the large CPA located at stressful area could be fronted with dangerous hemorrhage with minor injury. Therefore, careful surgical removal with the ligation of arteries should be recommended. Many cases of oral CPA have been primarily diagnosed as squamous cell carcinoma due to its awful features of superficial ulceration and deep bluish and pinkish color. But they may show no tumor induration but weak pulsation on touch.

Although it was known that the artery of CPA persistently remained as a dormant artery structure,^1,15) in the present CPA the smooth muscle layers of arteries and arterioles were thick with hyperplastic pericytes. In the observation of serial microsections it was clear that some arterioles were made by the luminal ingrowth of pericytes, and resulted multi-channels of arterioles in the vicinity of main artery. Particularly, in the periphery of CPA the arterioles gradually grew and penetrated into the adjacent muscles tissue. The arteries and arterioles of CPA were consistently positive for bFGF in their perivascular fibrous tissue, and diffusely positive for α-SMA in their vascular smooth muscle layer composed of pericytes. The α-SMA immunostain clearly disclosed the tortuous architecture of CPA, and more due to the weak immunoreaction of α-SMA it was indicated that the artery was old and became sclerosed. The sclerosed arteries were usually composed of thick intima layer but thin smooth muscle layer, and their lumens were almost obliterated. Therefore, with the findings of abundant pericyte growth and the immunoreactions of bFGF and α -SMA it was presumed that the present case of CPA might have a slow growing potential contrast to the common dormant nature of CPA.

The present CPA lesion was mainly composed of the tortuous artery and the associated arterioles without vein structure. The endothelial cell proliferation was minimum, and lymphatic was almost absent in the lesion. And the pinkish granular appearance in retromolar buccal mucosa showed no feature of epithelial tumor. In the immunohistochemistry the present vascular lesion was almost negative for PCNA, VEGF, CD31, CMG2, TGF-β1, HSP-70, and 14-3-3, indicating that the artery and arterioles were not actively proliferative, sparsely induced de novo angiogenesis, and was not in the degenerative cellular stress. Therefore, the present CPA could be differentially diagnosed from arteriovenous malformation, hemangioma, lymphangioma, and squamous cell carcinoma.

Actually CPA occurred in gastrointestinal tract is considered as a dangerous hemorrhagic lesion similar to hemangioma, but many CPLAs which were mostly small when detected were uneventfully treated with simple excision. But present retromolar buccal mucosa CPA was large in size, measuring about 20 × 25 mm, therefore, careful surgical treatment should be followed as soon as possible. The retromolar buccal mucosa CPA is first reported in this study and may present unusually clinical findings depending on its size and location. This asymptomatic lesion could be severely hemorrhagic by minor injury, therefore, precise differential diagnosis should be made through biopsy.