foramen rotundum

**Location and anatomy:** The foramen rotundum lies in the greater wing of the sphenoid, inferior and posterior to the superior orbital fissure and anteromedial to the foramen ovale. It opens from the middle cranial fossa (near the cavernous sinus) into the superior part of the pterygopalatine fossa, where V2 then divides.

**Contents:** Maxillary nerve (CN V2) is the main structure. Some sources also note small emissary veins and the artery of the foramen rotundum (a branch of the internal maxillary artery), but these are not high-yield.

**Mnemonic for skull base foramina (CN V2 and neighbors):** "Standing Room Only" = Superior orbital fissure (V1), foramen Rotundum (V2), foramen Ovale (V3). This follows the order anterior to posterior, medial to lateral arrangement of these openings. For foramen ovale contents, "OVALE": Otic ganglion (not transmitted but nearby), V3, Accessory meningeal artery, Lesser petrosal nerve, Emissary veins.

**Sensory distribution of V2:** Skin over the cheek, lower eyelid, lateral nose, and upper lip. It also supplies maxillary teeth (via superior alveolar nerves), maxillary sinus mucosa, nasal cavity mucosa, hard and soft palate, and the nasopharynx. Branches include the zygomatic, infraorbital (exits through the infraorbital foramen), superior alveolar, greater and lesser palatine, and posterior superior nasal nerves, plus the meningeal branch and pterygopalatine ganglion communicating branches.

**Clinical significance:** - **Trigeminal neuralgia:** Lancinating pain in the V2 (and/or V3) distribution, triggered by light touch, chewing, or cold. Usually caused by vascular compression of the trigeminal root (commonly the superior cerebellar artery). Treated with carbamazepine first line. - **Perineural tumor spread:** Head and neck cancers (e.g., adenoid cystic carcinoma, squamous cell carcinoma) can track along V2 through the foramen rotundum into the cavernous sinus and Meckel's cave. Imaging may show enlargement or enhancement of the foramen. - **Cavernous sinus pathology:** V2 runs in the lateral wall of the cavernous sinus, so thrombosis or tumor can cause V2 sensory loss along with CN III, IV, V1, and VI deficits. CN VI runs within the sinus itself, so it is often affected first. Internal carotid artery is also in the sinus. - **Nasopharyngeal angiofibroma and skull base lesions:** Can extend through the pterygopalatine fossa to the foramen rotundum. - **Anesthesia:** V2 blocks (via the pterygopalatine fossa) are used for maxillary and midface procedures.

**Exam pearls:** - V2 is purely sensory (V1 is also purely sensory; V3 is mixed with motor to muscles of mastication). - Foramen rotundum is a true canal-like foramen with a bony length, unlike the superior orbital fissure, which is a cleft. - V2 exits the pterygopalatine fossa through the inferior orbital fissure to become the infraorbital nerve. - Do not confuse with foramen spinosum (middle meningeal artery, meningeal branch of V3), which lies posterolateral to foramen ovale. Rupture of the middle meningeal artery at pterion causes epidural hematoma. - Foramen lacerum, carotid canal, and the internal acoustic meatus are other commonly tested skull base openings.

**Skull base openings summary (middle cranial fossa):** - Optic canal: CN II, ophthalmic artery - Superior orbital fissure: CN III, IV, V1, VI, ophthalmic veins - Foramen rotundum: CN V2 - Foramen ovale: CN V3, accessory meningeal artery, lesser petrosal nerve (variable) - Foramen spinosum: middle meningeal artery and vein, meningeal branch of V3