Abstract
Objective
The aim of this study is to present a case of superior oblique muscle dysfunction after a frontal sinus mini-trephine.
Methods
This is a case report of an 18-year-old woman where a mini-trephination approach and endoscope were used to open and marsupialize a symptomatic, opacified type IV cell within the left frontal sinus. After surgery, the patient developed a persisting diplopia; a left superior oblique muscle palsy was diagnosed. Nine cadaveric dissections of the trochlea were undertaken to clarify mechanisms for potential trochlear damage.
Results
Cadaveric dissection reveals that the trochlea is more than a simple pulley; it is a complex structure in close proximity to the orbital rim. The superior oblique tendon telescopes and is surrounded by a vascular sheath that could be easily traumatized.
Conclusion
Damage to the trochlea could occur, as the periosteum is elevated from bone or during healing. Alternatively, prolonged traction on soft tissue near the trochlea could cause swelling of the vascular sheath, fibrosis, and hypomobility of the superior oblique tendon. Careful siting of the incision for external frontal sinus surgery as well as careful retraction of skin flaps and periosteal elevation are all techniques used, which should reduce the risk of damage to the trochlea.
1
Introduction
Frontal sinus disease, which was typically managed with external procedures, is now usually managed endoscopically. Despite endoscopic advances, an external procedure such as a frontal sinus mini-trephine or an osteoplastic flap may still be required . A case is reported where a mini-trephination approach led to a superior oblique muscle palsy. A report on the anatomy and physiology of the trochlear as well as cadaveric dissections in the present study shows that trochlear anatomy should be carefully considered when designing external frontal sinus incisions as well as during surgery. These issues have been considered and discussed.
2
Case report
An 18-year-old woman presented with a history of recurring sinus infections and left frontal sinus pain. Previous left-sided endoscopic sinus surgery had been unsuccessful. Nasendoscopy showed a wide open left maxillary sinus ostium and 2 potential openings to the left frontal sinus. A computed tomographic scan showed an opacified type IV cell in the left frontal sinus ( Fig. 1 ). A combined internal-external approach was used to approach this cell . An incision was made under the left eyebrow ( Fig. 2 ), and the dissection continued down to bone. Periosteal flaps were raised; retraction of soft tissues was obtained with a self-retaining retractor and a circular opening (approximately 8 mm) made into the floor of the left frontal sinus. The opacified frontal cell was identified and removed. The frontal sinus was then identified and opened further from below. The external incision was closed in layers. Postoperatively, there was no swelling or hemorrhage ( Fig. 2 ). The patient noticed diplopia immediately after surgery, which improved after 4 to 6 weeks. However, some diplopia persisted at 3 months. Resulting tests showed a slight superior oblique underaction and resultant left hypertropia. This has been corrected with strabismus surgery.
2.1
Anatomical dissections
To clarify the mechanisms for potential trochlear damage, 9 anatomical dissections of the trochlea were performed; the structure of the trochlea was also examined histologically. The trochlea can be identified using bony anatomical landmarks. The trochlea can be identified 10.0 ± 0.9 mm inferior to the palpable superior orbital foramen in a medial direction just under the superomedial orbital margin ( Fig. 3 ) . The trochlea commonly attaches to the frontal bone in the trochlea fossa ; however, it may also attach to a trochlear spine . This spine was apparent in 2 of the dissections. The superior oblique muscle tendon then travels laterally along an oblique vector (within 1 mm) to the frontozygomatic suture .
The trochlear is also more than just a simple pulley . The superior oblique tendon is made up of separate fascicles, which telescope on each other ( Fig. 4 ); the central part of the tendon has a greater range of movement than the peripheral part . As the tendon moves within the concavity of the trochlea, the outer part of the tendon must move a greater distance than the inner part; how the tendon and the muscle achieves this is not known. A highly vascular sheath surrounds the intratrochlear portion of the tendon. It is the only extraocular muscle or tendon with such a rich vascular tunic; this sheath is postulated to meet the need for repair of “wear and tear” as well as for heat dissipation .
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
