Foramen Rotundum Duplication on High-Resolution CT. Case Report

Abstract

To report a case of an accessory canal arising from the floor of the foramen rotundum (FR) and extending to the infratemoral fossa. This case report describes the imaging findings of FR duplication on high-resolution CT in multiple planes. The FR is formed when the foramen anterius lacerum is divided into the superior orbital fissure and the FR inferiorly by an osseous spur arising from the sphenoid body. It has been hypothesized that FR duplication/fenestration, and accessory canal formation may be induced by adjacent bone spurs or vessels. This case reports the imaging appearance of FR duplication on multiplanar CT.

Introduction

The foramen rotundum (FR) is a short canal in the greater sphenoid wing at the skull base inferior to the superior orbital fissure. It connects the middle cranial fossa and the intracranial compartment with the pterygopalatine fossa (PPF) anteriorly [1, 2]. The FR runs along the lateral wall of the sphenoid sinus, and transmits the maxillary division (V2) of the trigeminal nerve from the cavernous sinus to the PPF [3]. In addition to V2, it contains the artery of the FR, and emissary veins [1, 4]. In the axial plane, the FR is a tube-like structure extending dorsal to ventral; in the coronal plane, the FR is round in appearance. This case report presents a case of FR duplication with the additional canal terminating in the infratemporal fossa, incidentally discovered on CT.

Case Report

A 42-year-old male presented to the emergency department with eye pain following altercation. CT scan of the maxillofacial structures was negative for fractures, and showed an incidental duplicated right FR (Fig. 1). The smaller accessory foramen arose from the FR cranial margin and extended anteriorly and laterally into the infratemporal fossa posterior to the pterygomaxillary fissure. The duplicated FR was inferior to the FR in the greater wing of sphenoid and superior to the sphenoid sinus right lateral recess.

Fig. 1
figure1

a Coronal CT image shows duplication of the right FR (black arrow) with inferior position of the accessory canal (white arrow). Note normal appearance of the left FR (white arrowhead). b Axial CT image shows the opening of the accessory foramen (white arrow) into the infratempotal fossa (white asterisk). The opening is posterior to the PPF (yellow asterisk) and the pterygomaxillary fissure. c Sagittal CT reconstruction through the accessory canal (white arrow) shows its origin from the floor of the proximal FR (black arrow), and its inferior course. The white asterisk denotes the PPF

Discussion

Embryologically, the FR is derived from the foramen lacerum anterius formed between the greater and lesser sphenoid wings [1]. An osseous spur arising from the sphenoid body divides the foramen lacerum anterius to the superior orbital fissure and the FR inferiorly [1]. It has been suggested that duplication or “fenestration” of V2 may be induced by chondrification or vascular structures at the skull base during morphogenesis [5].

Ginsberg et al. observed a similar anatomic variation in 16 of 98 patients on CT [1]. Specifically, they describe a small opening along the floor of the FR as in this case. In their study, the accessory canal, named “inferior rotundal canal,” terminates in the infratemporal fossa or between the pterygoid plates, and they suggest it could transmit emissary veins [1]. In the same series, a “lateral rotundal canal” was described in 8% of the cases extending to the infratemporal fossa [1]. This case most likely represents an “inferior rotundal canal,” as per Ginsberg et al. The only difference is that with improved scanner technology, the entire course of the canal on a single sagittal CT slice may be depicted, and this allows for the first time the visualization of the opening of the accessory canal in the infratemporal fossa posterior to the pterygomaxillary fissure. It may transmit emissary veins; however, the possibility of transmitting neuronal tissue cannot be excluded [1, 4]. No MRI was performed to identify any duplication of the maxillary division of the trigeminal nerve.

In an anatomic study, in approximately 1% of cases and almost always on the right, the FR has one opening in the middle cranial fossa, and there are two anterior openings; one in the PPF, and one in the orbit inferolateral to the superior orbital fissure following the course of a smaller accessory canal starting along the lateral wall of the FR [2, 4]. Rusu reported an intracranial duplication or “fenestration” of V2 anterior to the Meckel’s cave [5]. The additional nerve branch extended anteriorly through its own canal inferior to the FR into the PPF, where the branches joined [5].

Familiarity with anatomic variations at the skull base is important on imaging, and imperative for endoscopic surgical planning [5]. The contents of the duplicated foramen can only be speculated, and neuronal damage may be caused during surgery.

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SC: manuscript writing/editing

MK: project development, manuscript writing/editing

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Correspondence to Marinos Kontzialis.

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Cömert, S., Kontzialis, M. Foramen Rotundum Duplication on High-Resolution CT. Case Report. SN Compr. Clin. Med. 3, 692–693 (2021). https://doi.org/10.1007/s42399-021-00798-3

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Keywords

  • Foramen rotundum
  • Duplication
  • Accessory
  • Canal
  • CT