3D-Printable Files of the Sinus Anatomy and Skull

With hay fever season rapidly approaching in the northern hemisphere, embodi3D® is tackling the topic of the paranasal sinuses and portions of the upper skull. It's an autumnal celebration — embodi3D® style. Granted, we take on a number of arguably more interesting topics in our posts, and nasal and sinus anatomy should be fairly straightforward, right? After all, aren't these just openings and passageways in the skull that allow us to take in fresh air and exhale carbon dioxide? Not quite. This is human anatomy we're talking about, so nothing is ever as simple as one would assume, and the paranasal sinuses are certainly not an exception to this rule.

The paranasal sinuses have six primary parts, including the frontal sinus, ethmoid sinus, nasal cavity, maxillary sinus, and mucus membrane. These features allow us to efficiently take in air from the environment. But, as outlined in in a study titled CT of Anatomic Variants of the Paranasal Sinuses and Nasal Cavity: Poor Correlation With Radiologically Significant Rhinosinusitis but Importance in Surgical Planning, there are certain conditions that complicate breathing and prevent the paranasal sinuses from operating efficiently. These include Agger nasi cells, nasal septal deviation (deviated septum), and a condition in which the sphenoid sinuses extend into the posterior nasal septum. As these conditions can have chronic and significant impacts on a patient's quality of life, it's no wonder that paranasal sinus CT scans are among the most-request scans ordered by ENT outpatient departments. The study's authors were unable to find a difference that was statistically different among variations of patients with nasal cavity disease of paranasal sinus disease. This means that all those CT scans being ordered for cases of rhinitis or sinusitis are lacking in value unless a surgery is being planned. 

Some incredible files of a CT scan following superior maxillary surgery have been uploaded in the past. Could 3D-printed models using CT scans converted in STL files provide better results than CT scans alone? We'll let you decide. But, we're certain you'll form an opinion after viewing these excellent uploads to embodi3D®. Don't forget: to get the most out of these files and to create your own 3D-printed models. Register with embodi3D® today! It's free and takes just a few short minutes of your time. 

#1. A Half-Skull Available for Download in STL Format

An incredible 3D model of an half skull in half size uploaded by Dr. Mike. The paranasal sinuses (“the sinuses”) are air-filled cavities located within the bones of the face and around the nasal cavity and eyes. Each sinus is named for the bone in which it is located.  This example it´s perfect for teaching and as a discussion piece.
 

#2. Anatomy of the Paranasal Sinuses

This excellent 3D model uploaded by valchanov  shows:

Maxillary sinus- one sinus located within the bone of each cheek.

Ethmoid sinus- located under the bone of the inside corner of each eye, although this is often shown as a single sinus in diagrams, this is really a honeycomb-like structure of 6-12 small sinuses that is better appreciated on CT scan images through the face.

Frontal- one sinus per side, located within the bone of the forehead above the level of the eyes and nasal bridge.

Sphenoid- one sinus per side, located behind the ethmoid sinuses; the sphenoid is not seen in a head-on view but is better appreciated looking at a side view. 

#3. An Anatomically Precise 3D-Printed Nasal Cavity with Paranasal Sinuses

The pink-hued membranes lining the sinuses make mucus that is cleared out of the sinus cavities and drains into the nasal passage. The right and left nasal passages are separated in the middle by a vertical plate of cartilage and bone called the nasal septum. The sidewall of each nasal passage is lined by three ridges of tissue, and each of these is called a turbinate or concha. Specifically they are designated as inferior, middle, or superior depending on whether one is referring to the lower, middle, or upper structure. 

Most of the sinuses drain from underneath the middle turbinate, into a region called the osteomeatal complex. When air flows through the nasal passage on each side, it streams through the crevices between the nasal septum and these turbinates. Both airflow and mucus ends up in a part of the throat called the nasopharynx (the very back of the nose, where it meets the rest of the mouth and throat). Air is then breathed into the windpipe and lungs, while the mucus is swallowed.

#4. A CT Scan of Paranasal Sinuses Converted from a CT Scan DICOM

Other interesting structures associated with the nasal and sinus tract:

- Tear duct (called the nasolacrimal duct): drains tears from the inside corner of the eye into the nasal cavity.

- Eustachian tube: this is the tube responsible for clearing air pressure in the ears; it opens into the back of the sidewall of the nasopharynx.

- Adenoids: this is a collection of tonsil-like tissue that is found at the top of the nasopharynx beyond the very back of the nasal cavity. Although it can be large in children, this tissue usually goes away during puberty, although sometimes it does not and is then, at times, surgically removed for various reasons. 

#5. CT Scan of Chronic Sinusitis

In this CT scan we can see maxillary sinuses with sclerotic thickened bone (hyperostosis) involving the sinus wall. Chronic sinusitis is one of the more prevalent chronic illnesses in the United States, affecting persons of all age groups. It is an inflammatory process that involves the paranasal sinuses and persists for 12 weeks or longer. The literature has supported that chronic sinusitis is almost always accompanied by concurrent nasal airway inflammation and is often preceded by rhinitis symptoms; thus, the term chronic rhinosinusitis (CRS) has evolved to more accurately describe this condition.

Diagnostic Considerations

- Problems to be considered include the following:

- Temporomandibular joint syndrome

- Asthma

- Other chronic rhinitis

- Nasal and sinus cavity tumors

- Facial pain and headache attributable to other causes

- Nasal polyp

- Dental infection

- Periodontal abscess

- Antral-choanal polyp

- Inverting papilloma

- Aspirin/nonsteroidal anti-inflammatory drug sensitivity

- Chronic headache of other etiology

#6. A CT Scan of the Paranasal Sinuses

In the article mentioned above the most common anatomic variant of the sinonasal cavities was deviation of the nasal septum, which was present in 98.4% of the patients but was considered to be more than minimal in 61.4%.

The second most common variant was Agger nasi cells, which were present in 83.3% of patients, falling within the wide range of 3–100% reported in previous studies . Agger nasi cells were also the second most common variant that occurred bilaterally in our study.

The third most common variant was extension of the sphenoid sinuses into the posterior nasal septum resulting in some degree of pneumatization of the posterior nasal septum (76.0%).

The fourth most common variant was sphenoid sinus pneumatization extending posterior to the floor of the sella turcica (68.8%), which was defined as air extending more than halfway beyond the middle of the sellar floor toward the dorsum sella. 

The prevalence of pneumatization of the anterior clinoid process in our study was 16.7%, which is commensurate with the prevalence of 4–29.3% described in the literature .

The prevalences of concha bullosa at 26.0% in our study (14–67.5% previously reported), pneumatized lamina of the middle turbinate at 37.0% (9.6–46.2% previously reported) 

#7. An Excellent 3D Model of the Skull in a Sagittal View

Identification of some anatomic variants is crucial in the planning of functional endoscopic sinus or other skull base surgery, because the presence of these variants may influence the surgical approach. Most notably, the presence of sphenoethmoidal (Onodi) cells is associated with increased risk of injury to the optic nerves or carotid arteries during functional endoscopic sinus surgery and with other transsphenoidal and skull base procedures.

Endoscopic sinus surgery (ESS) is one of the most common procedures done by otolaryngologists, so achieving a certain competency level in performing this procedure is crucial during the residency program. Moreover, ESS is considered a challenging procedure, especially surgery in the frontal sinus and the frontal recess, which remains the most challenging region of sinus surgery due to the variability and very complex nature of the cellular patterns. To overcome these challenges, simulation technology has emerged as a reasonable approach. A  3D-printed simulator currently developed in a work titled Development and validation of a 3D-printed model of the ostiomeatal complex and frontal sinus for endoscopic sinus surgery training proved to have realistic haptic feedback, especially for the bony dissection. As for the physical appearance, the realism of the anatomy scored high and this is  correlated with the ability of the model to enhance 3D learning as was reported by the participants.

References

1. Shpilberg, K. A., Daniel, S. C., Doshi, A. H., Lawson, W., & Som, P. M. (2015). CT of anatomic variants of the paranasal sinuses and nasal cavity: poor correlation with radiologically significant rhinosinusitis but importance in surgical planning. American Journal of Roentgenology, 204(6), 1255-1260.

2. Alrasheed, A. S., Nguyen, L. H., Mongeau, L., Funnell, W. R. J., & Tewfik, M. A. (2017, August). Development and validation of a 3D‐printed model of the ostiomeatal complex and frontal sinus for endoscopic sinus surgery training. In International forum of allergy & rhinology (Vol. 7, No. 8, pp. 837-841).