Pure orbital floor fractures account for approximately 67–84 % of all orbital trauma cases [
1,
3]. Occasionally, history or clinical examination alone may be inadequate to raise the suspicion of a retained periorbital foreign body. Therefore, CT is important for the evaluation of periorbital injuries [
2]. The clinical course and indications for removal of the periorbital foreign body depend on a variety of factors, such as its position (near vital structures), chemical structure (many metals and plastic materials may be inert, whereas wood is associated with a higher incidence of complications), potentially infectious nature, or clinical findings (displacement or damage to vital anatomical structures and ophthalmological evaluation findings) [
4,
8]. In some periorbital trauma the foreign body is dislocated in the maxillary sinus; many authors suggested its removal to prevent future infections [
9,
10]. However, infection is not a certain outcome since sinuses have been observed to be healthy despite the inclusion of foreign materials [
11]. The sinus can remain asymptomatic for several months before an acute infection develops. The removal of the foreign body is considered necessary because of peculiarities of the topographic anatomy of the maxillary sinus. The close proximity of the external posterior wall to the pterygopalatine fossa lodging the main trunk of the second division of the trigeminal nerve (the maxillary nerve), maxillary artery, and venos plexus connected with the orbit and cavernous sinus of the dura mater may promote the spread of pathology from the maxillary sinus to this region [
12]. The superior wall of the maxillary sinus separates it from the orbit. On the surface of the wall lies a canal (sometimes a semicanal), which opens into the maxillary cavity and contains the maxillary nerve and vessels. Therefore, pathological conditions of the sinus may affect this vascular-nerve bundle or spread into the orbit [
12]. Also the trigemino-cardiac reflex (TCR) reported by some authors is considered an indication for the removal of the intraorbital foreign body [
13,
14]
. Ophthalmological findings include the presence of double vision (Hess–Lancaster evaluation), enophthalmos/hypoglobus, and conjunctival ecchymosis [
15].
With regard to radiological evaluation, CT is ideal for evaluating fractures of the orbital walls and the integrity of the adjacent sinuses [
2]. Three-dimensional reconstruction after image acquisition allows categorization of the size and shape of fracture, thus aiding in surgical treatment planning [
2]. Periorbital foreign bodies can be distinctly observed on CT, which remains the most sensitive study and should be the first imaging modality in such cases [
16,
17]. We initially suspected a periorbital surface injury in our patient, and we considered CT to verify our suspicion of an orbital floor fracture, not to evaluate the potential presence of a periorbital foreign body. We were surprised to observe that a sizeable periorbital foreign body such as a plastic pen cap could find its way into the sinus through a small entry site, without showing major clinical manifestations such as sinusitis or sinus infection. The previous surgical treatment (orbital frame sutures) did not consider radiological findings; therefore, it was inadequate. Generally, the indications for surgical removal of foreign bodies include neurological compromise, mechanical restriction of ocular movements, development of acute or chronic infection, or chronic suppurative reactions, such as those observed with copper foreign bodies [
18]. Removal of foreign bodies located close to the apex is also generally discouraged, because the risk of collateral damage far outweighs the benefits [
19]. In our patient, surgical removal was considered to prevent sinus and periorbital infections.