Anatomy, Head and Neck, Sphenopalatine Artery

Structure and Function

The SPA is a terminal branch of the maxillary artery, which arises from the external carotid artery.[5] The maxillary artery is classically divided into 3 segments: mandibular, pterygoid, and pterygopalatine. The SPA originates from the pterygopalatine segment of the maxillary artery within the pterygopalatine fossa (see Image. Plan of the Maxillary Artery Branches).[6] The pterygopalatine fossa lies posterior to the medial wall of the maxillary sinus and contains the maxillary artery and nerve, as well as the pterygopalatine ganglion, collectively forming the principal neurovascular conduit to the nasal cavity.

From its origin, the SPA courses medially and anteriorly through the pterygopalatine fossa toward the sphenopalatine foramen to enter the nasal cavity (see Image. Nasal Cavity Blood Supply).[7][8][9] The borders of the sphenopalatine foramen include the body of the sphenoid superiorly, the orbital process of the palatine bone anteriorly, the sphenoidal process posteriorly, and the perpendicular plate of the palatine bone inferiorly.

Although positional variability exists, the foramen is most commonly located at the junction between the middle and superior meatus (see Image. Sphenopalatine Foramen). This location is frequently just superior to the posterior end of the horizontal lamella of the middle turbinate. The ethmoidal crest of the palatine bone lies immediately anterior to the foramen and serves as a reliable landmark for endoscopic identification. In most individuals, the foramen is located posterior to the ethmoidal crest. Several studies describe accessory foramina, reflecting the frequent branching of the SPA before entry into the nasal cavity.

The SPA demonstrates considerable anatomic variability. About 1 to 10 branches may arise, with more than 2 present in 97% of individuals and more than 3 identified in 67%. Branching may occur before the artery reaches the sphenopalatine foramen. In approximately 42% of specimens, early division produces separate bony foramina.

Immediately medial to the crista ethmoidalis, 2 or more branches are identified in the majority of cases. At least 3 branches are present in 67% of individuals, while 4 or more branches occur in approximately 1/3. Despite variability in branch number and distribution, 2 principal vessels are consistently described: the posterior septal and posterior lateral nasal.[10]

The posterior septal artery crosses the anteroinferior margin of the sphenoid sinus and supplies the posterior nasal septum. The posterior lateral nasal artery descends along the perpendicular plate of the palatine bone toward the posterior end of the middle turbinate. This vessel continues inferiorly to supply the middle and inferior turbinates and the lateral nasal wall.[11] The posterior lateral nasal artery serves as the dominant arterial supply to the lateral nasal wall. Therefore, surgical management of refractory epistaxis requires ligation of this artery proximal to the branch supplying the middle turbinate.

The SPA provides the primary arterial supply to the nasal cavity, accounting for up to 90% of mucosal perfusion. The artery irrigates the lateral nasal wall, the superior, middle, and inferior turbinates, the fontanelle regions, and the posterior 2/3 of the nasal septum.[12] The anterior and superior portions of the septum receive blood from the anterior and posterior ethmoidal arteries. The ethmoidal artery originates from the ophthalmic artery, which derives from the internal carotid artery.

Within the nasal septum, the SPA participates in an extensive anastomotic network. The Kiesselbach plexus, or the Little area, represents the convergence of branches from both the internal (anterior and posterior ethmoidal arteries) and external (superior labial artery, greater palatine artery, and posterior septal branch of the SPA) carotid arteries (see Image. Arterial and Venous Anatomy of the Head and Neck).[13]

Embryology

During developmental weeks 4 and 5, the aortic sac gives rise to the aortic (pharyngeal) arches. The maxillary artery emerges from the mesoderm of the 1st aortic arch and subsequently gives rise to the SPA. The number of developing branches and the diameter of the SPA determine the number and morphology of the sphenopalatine foramina in the palatine bone.[14]

Nerves

The maxillary nerve constitutes the 2nd branch of the trigeminal nerve (cranial nerve V2) and courses in proximity to the maxillary artery. The nerve extends from the middle cranial fossa into the pterygopalatine fossa via the foramen rotundum.[15] Within the pterygopalatine fossa, the maxillary nerve gives rise to multiple branches, including the infraorbital, nasopalatine, zygomatic, superior alveolar, pharyngeal, and the greater and lesser palatine nerves. The maxillary nerve also establishes communication with the pterygopalatine ganglion, which is suspended by 2 small trunks termed the "pterygopalatine nerves."[16]

The pterygopalatine ganglion resides deep within the pterygopalatine fossa near the sphenopalatine foramen.[17] The ganglion is the largest parasympathetic structure associated with the maxillary nerve branches and receives preganglionic input primarily from the greater petrosal branch of the facial nerve (cranial nerve VII) via the Vidian nerve.

The Vidian nerve forms from the junction of the greater petrosal nerve, containing preganglionic parasympathetic fibers, and the deep petrosal nerve, originating from the carotid plexus and containing postganglionic sympathetic fibers. Only the preganglionic parasympathetic fibers synapse within the pterygopalatine ganglion. Postganglionic parasympathetic fibers distribute through their respective branches to provide secretomotor innervation to the lacrimal gland and mucosal glands of the oral cavity, nose, and pharynx.[18]

The nasopalatine branch courses alongside the SPA and enters the nasal cavity through the sphenopalatine foramen. This nerve travels across the roof of the nasal cavity, inferior to the sphenoid sinus orifice, to reach the septum. The nasopalatine nerve then proceeds obliquely between the periosteum and mucous membrane of the lower septum to connect with the greater palatine nerve.[19]

Physiologic Variants

SPA anatomy has been studied extensively in numerous cadaveric investigations. Around 97% of these studies demonstrate at least 2 arterial branches at the plane of the sphenopalatine foramen. These branches correspond to the posterior lateral and septal arteries, as described previously. Although 2 to 4 SPA branches are most commonly observed, studies occasionally demonstrate up to 10 branches. After exiting the sphenopalatine foramen, distal and posterolateral branches demonstrate greater variability. Some segments of the artery may course anterior to the posterior maxillary wall.

The arrangement of arterial branches exhibits considerable variability, with distributions superior or inferior to the ethmoidal spine, crisscrossing upon exiting the foramen, and demonstrating asymmetry between nasal cavities within the same cadaver. The ethmoidal crest provides a consistent landmark for orientation within the nasal cavity, independent of variation in SPA branching patterns.[20]

Surgical Considerations

Sphenopalatine Artery Ligation

Surgical management of epistaxis is indicated for patients whose bleeding is refractory to conservative therapies. Detailed knowledge of vascular anatomy and adjacent landmarks is essential to prevent surgical failure and reduce the risk of postoperative hemorrhage.

SPA exposure may be achieved endoscopically by elevating a posterolateral mucosal flap over the orbital process of the palatine bone. A vertical incision is placed inferior to the posterior portion of the middle turbinate, approximately 1 cm anterior to its posterior tip. Elevation of the mucoperiosteal flap posteriorly and superiorly exposes the ethmoid crest, which serves as a reliable landmark for SPA localization and is consistently positioned anteromedial to the sphenopalatine foramen. Resection of the ethmoid crest improves visualization of the SPA and facilitates identification of its terminal branches. 

During flap elevation and ethmoid crest resection, the fibro-neurovascular bundle containing the SPA and nasopalatine nerve becomes accessible at the sphenopalatine foramen. After isolation, the artery and its branches may be managed by bipolar cauterization, clip occlusion, or a combination of both. If distal bleeding persists, SPA tracing proximally through the sphenopalatine foramen into the pterygopalatine fossa permits ligation before terminal bifurcation.

Upon achieving hemostasis, the mucoperiosteal flap is repositioned and covered with an oxidized cellulose polymer hemostatic agent. Anatomical variations in SPA branching and the presence of multiple foramina can produce variable responses to SPA ligation.

Nasoseptal Flap

The nasoseptal flap represents a surgical technique for skull base reconstruction following anterior skull base tumor resection, transsphenoidal pituitary adenoma removal, and repair of sella and clival cerebrospinal fluid (CSF) leaks.[21] The flap functions as an effective barrier to prevent CSF leakage. The flap is pedicled on the posterior septal artery, a terminal branch of the SPA. A midseptum mucoperiosteal flap is incised inferiorly along the maxillary crest and dorsally beneath the olfactory epithelium. The posterior septal flap, pedicled on the posterior septal branch, is rotated around the pedicle into the defect. The septal branch–based blood supply ensures reliable revascularization and robust coverage for skull base reconstruction.[22]

Clinical Significance

Posterior Epistaxis

The SPA carries the largest volume of blood to the nasal cavity and serves as the source of most posteriorly based epistaxis. Posterior epistaxis accounts for approximately 10% of cases, with 80% of bleeding originating from SPA. This type of bleeding is most often associated with atherosclerotic disease, hypertension, and diabetes but may also occur from iatrogenic or idiopathic causes. Posterior hemorrhage may remain asymptomatic or present insidiously as hematemesis, anemia, or melena.

Additional clinical features of posterior epistaxis include blood in the oropharynx, recurrent episodes of epistaxis, failure to control bleeding with nasal packing, clots near the sphenopalatine foramen, clots in the maxillary sinus ostium, and absence of anterior septal bleeding. Management of posterior epistaxis is challenging due to the inaccessible location of the bleeding vessel.[23] The SPA is not readily visualized with anterior nasal speculum examination and is often identified only through nasal endoscopy.

Traditional management of posterior epistaxis includes anteroposterior nasal packing and balloon catheterization. Posterior nasal packing involves placement of a postnasal pack in the nasopharynx, occluding the posterior choana, combined with firm anterior nasal packing extending deeply into the nasal cavity. Hemostasis is achieved through direct pressure on the bleeding vessel. Nasal balloon catheters allow easier insertion, cause less discomfort, and provide targeted pressure at the point of maximal bleeding. This method reduces the compressive effect on the entire mucosal surface, thereby lowering the risk of mucosal ischemia. In cases of severe or refractory bleeding, direct cauterization, embolization, or ligation of the responsible vessel may be required. 

Juvenile Nasopharyngeal Angiofibroma

Juvenile nasopharyngeal angiofibroma (JNA) is an uncommon benign tumor originating from the lateral nasal wall near the sphenopalatine foramen. The tumor predominantly affects adolescent boys and exhibits local aggressiveness, frequently invading surrounding structures and tissues. JNA typically presents with painless, progressive unilateral nasal obstruction, epistaxis, and rhinorrhea. The tumor receives a rich vascular supply, primarily from the SPA. Macroscopically, JNA appears as a rounded, circumscribed, nonencapsulated, mucosa-covered mass. Microscopically, the tumor demonstrates erratically arranged collagen and an irregular vascular pattern. Due to the extensive vascularization, embolization of the SPA followed by surgical resection yields a favorable prognosis when the tumor is diagnosed promptly.[24][25]