Hertel measurements

An exophthalmometer is used to measure the prominence of the eye. The most common exophthalmometer used is the Hertel exophthalmometer (Figure 14-1). The Hertel exophthalmometer measures the anterior projection of the eye, from the lateral orbital rim to the cornea (Table 14-1). When you use the Hertel exophthalmometer, be sure to lightly push the instrument against the lateral orbital rim and make the width or base setting of the exophthalmometer as narrow as comfortable for the patient. Try to use the same base setting for an individual patient each time you measure the prominence of the eye. Remember that measurements with the Hertel exophthalmometer are not exact, but you should be able to obtain repeatable measurements within 1–2 mm. When you learn to use the Hertel exophthalmometer, compare your readings with those of a more experienced examiner so that you can make sure you are measuring correctly. As the Hertel exophthalmometer uses the lateral orbital rim at a reference point, any surgery, disease, or trauma that changes the position of the lateral rim will affect the Hertel measurements. In cases where the lateral rim is not in normal position, you can use an exophthalmometer designed by Thomas Naugle. This device uses the forehead and cheek as reference points.

Figure 14-1 Hertel exophthalmometer measures the distance from the lateral canthal angle to the anterior surface of the cornea.

Table 14-1 Average Hertel measurements

Race and facial bone structure

The normal prominence of the eye in the orbit depends upon the surrounding facial bones. The bony structures vary from individual to individual and among races. The equator of the globe is at the lateral orbital rim in a white patient with average bone structure. You can appreciate the position of the eye relative to the rim during the physical examination by placing your index finger at the lateral orbital rim and pushing against the eye. The average Hertel measurement for a white patient is 20 mm. The Asian face shows less prominent eyes. The average Hertel measurement for an Asian patient is approximately 18 mm. The African American face shows relatively more prominent eyes. The maxilla is shallow compared with white or Asian facial bones. The average Hertel measurement in an African American patient is 22 mm.

Significant measurements: asymmetry and change over time

Because the normal position of the eye in the orbit varies from patient to patient, we are more interested in asymmetry in the prominence of the one eye compared with the other or a change in the globe position on one side that has occurred over time. Proptosis implies an anterior displacement of the globe. An orbital mass not centered within the orbit will displace the eye off axis as well. Globe ptosis is the term used when the eye is pushed down by a mass. As you perform the orbital examination, look for signs of axial and nonaxial globe displacement of the eye that will help you locate the mass that is displacing the globe.

The surgical spaces of the orbit

The orbit is conceptually and anatomically divided into surgical spaces (Box 14-1).

The intraconal space, sometimes called the central surgical space, contains the optic nerve and orbital fat (Figure 14-2). Many tumors arise within the intraconal space or push their way into this space. The most widely discussed tumors of the orbit, optic nerve glioma and optic nerve meningioma, occur in the intraconal space.

Figure 14-2 The surgical spaces of the orbit: intraconal space (central surgical space); extraocular muscles; extraconal space (peripheral surgical space); subperiosteal space; Tenon’s space; the extraorbital space (including periocular tissues, brain, nose, sinuses, bone, and surrounding soft tissues). (A) Axial view. (B) Coronal view.

The extraconal space, sometimes called the peripheral surgical space, contains the lacrimal gland, the superior oblique muscle and trochlea, and nerves and vessels in the extraconal orbital fat. The lacrimal gland is a common source of orbital pathologic processes. An enlarged lacrimal gland is often palpable in the upper lid and is readily accessible using an anterior orbitotomy through the upper lid skin crease.

A fibrous membrane, the intermuscular septum, extends between the anterior portion of the extraocular muscles, separating the intraconal and extraconal spaces. The muscles can become involved in neoplastic or inflammatory processes. The most common condition is thyroid orbitopathy. Painful inflammation of the muscles, myositis, may also occur. Primary neoplasms of the muscles are very rare, but metastatic lesions occur more commonly.

The subperiosteal space is a potential space between the orbital bones and the periorbita. A hematoma may collect in this space from an adjacent fracture. A collection of pus, a subperiosteal abscess, may collect medially from an adjacent ethmoid sinus infection.

Tenon’s space lies between the eye and the fibrous capsule. Tenon’s capsule, which surrounds all but the anterior portion of the eye, is the bloodless space in which enucleation and scleral buckle procedures are performed. This space is rarely involved in orbital pathologic processes, the most common lesion being extraocular extension of a choroidal melanoma.

The extraorbital space, or periocular tissue, includes all the structures surrounding the orbit: bone, brain, sinuses, nasal, skin, and conjunctiva. A variety of problems originate in these tissues and involve the orbit secondarily. We will talk about some of these conditions at the end of this chapter (Table 14-2).

Table 14-2 Differential diagnosis based on direction of globe displacement in adults

The “P’s” of the orbital history and physical examination

Krohel, Stewart, and Chavis described the familiar mnemonic involving the “P’s” of the orbital history and physical examination. Although this system is somewhat contrived, it is a useful way to learn the orbital history and conduct the physical examination, providing a checklist of what to consider. The six P’s they described are the following:

We will see in a few paragraphs that we should add a seventh P to the list, past medical history.

Pain and progression

Pain and progression are the characteristics of the orbital problems that you will find most helpful in developing the differential diagnosis. Pain is caused by inflammation, infection, acute pressure changes, and bone or nerve involvement. Once you become familiar with the common orbital disorders, you will find that the presence or absence of pain is very helpful in developing a differential diagnosis.

Progression is the other “P” that will refine the differential diagnosis easily for you. As you can imagine, some processes progress quickly, whereas others take months or years to develop. You can classify progression into:

History as a clue to the pathologic process

It is impossible to diagnose every cause of proptosis based on pain and progression only, but you will be surprised how easy it is to develop a differential diagnosis of a general pathogenesis. Consider the types of pathologic processes that affect the body as a whole. You probably learned these in your medical school pathology course:

Now consider how the symptom of pain fits into the categories. Pain suggests inflammation, infection, hemorrhage, or perhaps a tumor growing into nerves or bone. Neoplasms, in general, do not cause pain until a complication related to the neoplasm arises. You will remember from your general surgery days in medical school that the large bowel tumor sits quietly in the abdomen until there is an obstruction that causes secondary inflammation, infection, or hemorrhage. This is true of orbital tumors as well. The majority of orbital neoplasms do not cause pain until late in their course.

A sudden onset with rapid progression over minutes suggests a hemorrhage (Figure 14-3). Acute processes occurring over hours to days suggest inflammation or infection. Slower processes occurring over weeks to months suggest more chronic types of inflammatory processes such as thyroid disease. Chronic conditions with a vague onset and slow progression over months suggest a benign neoplasm or lymphoma.

Figure 14-3 Spontaneous orbital hemorrhage. (A) Pain and proptosis developed over minutes with no progression after the initial presentation. (B) CT scan demonstrates a well-circumscribed mass (based on axial and coronal cuts). Drainage of the hematoma was required because of pain (see Figure 15-12). No etiology was determined.

Onset and progression of symptoms and signs are related features. Onset identifies a point in time when the problem started and how it manifested itself initially. Progression describes any change in the symptoms (and the rate of change) occurring over the period of time since the onset. For example, an orbital infection may have an onset 3 days after the start of a respiratory infection. The pain and inflammation are minimal initially, but progress rapidly after onset. A contrasting example is the proptosis and globe ptosis resulting from a benign mixed tumor of the lacrimal gland. The progression is so slow, over months or years, that it is difficult for the patient to identify the exact onset of any symptoms. In many chronic conditions, the patient’s perception of the onset and the progression of the disorder may not be accurate. In these cases, the patient’s perception of onset is often when the proptosis was noted, which may not be when the process actually started. In these cases, the use of the so-called family album tomogram (FAT) scan is useful. The review of these old photos can help to identify the true progression of a disorder.

Past medical history

Lastly, we should add past medical history to the list of the original six P’s. Any previous diagnosis of neoplasm elsewhere in the body must be noted. Past trauma of the face may have caused some facial asymmetry that may accentuate or diminish the appearance of a proptotic eye. Any history of thyroid disease that has already been diagnosed should be noted. This is perhaps the most important information to solicit. Don’t forget to include basic information in the history such as age and sex. You will see that most orbital processes tend to occur at certain ages. The differential diagnoses of childhood and adult orbital disorders don’t share many diseases in common. The most common disorder that has a striking sex difference is thyroid disease, which occurs about six times more often in women than in men.

A typical history might be written, “A 65-year-old noted proptosis of the left eye and a mass in the lid 4 months ago. Since that time the proptosis and swelling have progressed slowly. There is no pain. There is no past medical history of trauma or thyroid disease. He was treated for lymphoma in the past. He is currently taking no medications.” Are you getting the idea? Already you are thinking about the possibility of orbital lymphoma and will be looking for some fullness of the superior fornix, a little globe ptosis, and a palpably enlarged lacrimal gland during the physical examination.

The physical examination “P’s”

The “Ps” of the orbital examination are:

Proptosis

The most important part of the orbital examination is the evaluation of the proptotic eye. An orbital mass or volume-producing process “pushes” the eye away. The larger the mass is, the more displacement of the globe.

In most cases, when we talk about proptosis, we are really talking about proptosis or an axial displacement of the eye in an anterior direction. When you see axial proptosis, think of thyroid orbitopathy with enlargement of the extraocular muscles. Other intraconal disorders such as optic nerve tumors or a benign cavernous hemangioma may occur within that muscle cone as well and cause axial anterior displacement of the eye. In some conditions, you will see nonaxial displacement of the eye. If you see the eye pushed downward, think of problems arising in the area of the lacrimal gland or, less commonly, defects in the orbital roof due to trauma, encephalocele, or frontal sinus mucocele formation. When you see the eye displaced laterally, there is usually a problem in the ethmoid sinus. The most common situation that displaces the eye laterally is a subperiosteal abscess (an acute process) arising in the ethmoid sinus and extending into the subperiosteal space. Rarely, sinus carcinomas (a slowly progressive process) or mucoceles (a very slowly progressive process) of the ethmoid sinus can cause this type of lateral displacement. You will rarely see the eye being displaced upward. A number of rare conditions can cause this (Figure 14-4). Although lymphoid lesions occur most commonly in the superior orbit, lymphoid lesions are so common that they are the most common cause of an inferior orbital mass. Rarely, tumors arising from the maxillary sinus can erode through the orbital floor and push the eye upward. Likewise, it is rare to see the globe pushed medially. If medial globe displacement is present, the eye usually is also being pushed downward by an enlarged lacrimal gland. You can estimate the nonaxial displacement of the eye with a ruler or use an instrument designed for this purpose known as the McCoy Tri-Square (P-3795, Jarit Instruments, http://www.jarit.com) (Figure 14-5).

Figure 14-4 Globe displacement. (A) Superior displacement of the right eye. (B) CT scan shows a well-circumscribed mass, determined to be an unusual mesenchymal tumor after excisional biopsy.

Figure 14-5 McCoy Tri-Square measuring millimeters of globe ptosis.

There is an exception to the rule that an orbital mass pushes the eye away from the mass. Scirrhous carcinoma of the breast is an infiltrative sclerosing tumor, which may actually cause an enophthalmos of the eye. You have already asked about past medical history of other carcinomas, so if you heard that the patient has a history of breast carcinoma and you note that eye is sunken, think of metastatic breast cancer (Figure 14-6).

Figure 14-6 Enophthalmos secondary to metastatic breast cancer. (A) Note slight enophthalmos of the left eye. (B) CT scan shows an infiltrative orbital mass.

We have already talked about the use of the Hertel exophthalmometer to measure the prominence of the eye. Remember that there are normal variations among individuals and races. When you use the Hertel exophthalmometer, asymmetry between the left and right sides is more important than the actual measurement. Any asymmetry measuring more than 2 mm is significant. Don’t forget that trauma or congenital variation may be a cause of the asymmetry. Similarly, a change in the displacement of the eye based on the patient’s history or old photographs is an important finding.

Palpation

The next step in the orbital examination is palpation. Start with palpation of the orbital rims and then move toward the eye, palpating the superior and inferior fornix for any anterior masses. If a mass is palpable, you want to note its shape, size, and position. Often, you can tell if the mass has a smooth border separate from adjacent tissues or is infiltrating into adjacent tissues. In some patients, the mass will be fixed to bone or a nearby structure such as an extraocular muscle, suggesting an infiltrative tumor. You should try to determine if there is any tenderness in the area of the lesion as well. Infectious or inflammatory disorders will often cause the skin to be erythematous and warm to touch.

Pulsation

Pulsations of the orbit are rare but, when present, are diagnostic. A classic finding is pulsatile proptosis. This pulsation of the eye suggests either an arterial vascular malformation in the orbit or the absence of orbital bone that allows the normal pulsations of the brain to push on the eye. The most common cause of pulsatile proptosis is the absence of the sphenoid wing seen in neurofibromatosis. If you think you are seeing a case of pulsating exophthalmos, you will find it useful to confirm the globe pulsations using the Hertel exophthalmometer to view the eye from the side. Feel the radial pulse at the same time and you will see that the pulsations are synchronized.

Orbital arterial vascular lesions can pulsate. If the flow is high, you may be able to hear a bruit or feel a thrill. These lesions are rare also. Vascular abnormalities that are primarily venous are more common than arterial lesions. Venous lesions do not pulsate, but they will usually show enlargement with the Valsalva maneuver or with the head in a dependent position (Figure 14-7).

Figure 14-7 Valsalva maneuver causing swelling of the lid in a patient with a large orbital varix. (A) Eyelid without Valsalva maneuver. (B) Eyelid swelling with Valsalva maneuver. (C) Conjunctival varix engorgement with Valsalva maneuver. (D) CT scan showing nondiscrete orbital mass. Note phleboliths and enlargement of the superior orbital fissure.

Periocular changes

The last point to note in the orbital examination is periocular changes. These include a variety of abnormalities in the skin, conjunctiva, eye, or surrounding periocular tissues. Some periocular changes that are most useful for diagnosis are the temporal flare of the lateral portion of the upper lid and lid lag seen on downgaze in patients with thyroid orbitopathy (Figure 14-8). Other examples of periocular changes include a conjunctival salmon patch suggesting orbital lymphoma (see Figure 14-18), fullness of the temple suggesting a sphenoid wing meningioma (see Figure 14-22), and periocular skin malignancy suggesting intraorbital spread of cutaneous carcinoma.

Figure 14-8 Periocular changes associated with thyroid orbitopathy. (A) Right upper lid retraction and temporal flare of the lateral upper eyelid, suggesting thyroid orbitopathy. (B) Lid lag on downgaze in the same patient.

At this point, stop and think about the orbital examination and remind yourself of how you will proceed:

Proptosis? Order a CT scan

Almost all patients with proptosis will require orbital imaging. One exception to this may be the patient with findings typical of stable Graves’ disease in whom the diagnosis is so apparent that no imaging is needed to confirm your clinical suspicion. CT scanning is used as the primary imaging technique for evaluation of any patient with proptosis. You should order a magnetic resonance imaging (MRI) scan of the orbit in special cases, primarily those situations in which imaging of the orbital apex and chiasm is required.

You are undoubtedly familiar with the CT scan technique. You will recall that CT scanning uses ionizing radiation passed through the tissue to form a computer-generated radiograph. Like other radiographs, excellent views of the bony structure are obtained, making the CT scan the method of choice for viewing bony orbital trauma. Remember that fat is radiolucent (black) on a CT scan. The intraconal fat gives a good natural contrast with adjacent soft tissue structures (shades of gray) without any injection of intravenous contrast agents. For these reasons, the CT scan gives excellent views of the orbital bones and the majority of orbital structures.

CT scan is essential for evaluation of orbital trauma. CT scans are readily available. Helical CT scanners have reduced orbital scanning times to less than a minute per patient. You should order and review axial and coronal projections on all patients. Sagittal views are occasionally helpful. All projections are available without repositioning the patient. You hospital or imaging center should be providing high resolution orbital scans with no more than 1–2 mm cuts. The cavernous sinuses and paranasal sinuses should be included with orbital scans. You will want intravenous contrast agent for evaluation of most tumors. Contrast allergies are not uncommon, so make sure you ask about iodine or fish allergies. CT scanning remains significantly less expensive than MRI.

Magnetic resonance imaging

Generation of images is based on entirely different principles than those used in CT scanning. No ionizing radiation is used. An image is generated based upon the “vibration” of protons in tissue when a patient is placed in the magnetic field and then subjected to a series of radio wave pulses. The radiologist can vary the radio wave pulses so that different tissues generate signals (this is how the standard T1- and T2-weighted scans, and the many other specialized sequences, are generated). Some general imaging characteristics will help you to interpret MRI scans:

The resolution for MRI is less than for CT. The tissue contrast, however, is better with MRI. As the fat provides a contrast to most other structures, CT can be used as the main screening technique for orbital disease. MRI plays an important role in the evaluation of specific orbital diseases and is sometimes used in addition to CT scan.

The main indication for MRI is to view the orbitocranial junction. If you suspect an optical nerve tumor, you should request an MRI scan. Because bone is not visualized, the bony artifact from the dense bones of the orbital apex seen on CT scans is not present. The soft tissues of the apex are visualized in detail. Some intraorbital organic foreign bodies are seen better with MRI scans than with CT scans. Vascular tumors or other very heterogeneous tumors are often seen more clearly on an MRI scan than on a CT scan, as well. Lastly, any secondary orbital disease originating from the brain or paranasal sinus can often be visualized best by both CT and MRI together. This allows the best view of bone and soft tissue. In the case of sinus neoplasms extending into the orbit, T2-weighted MRI sequences help to distinguish sinus opacity caused mucous retention (bright signal) from that caused by tumor (dark signal).

Most radiology departments have routine imaging sequences that are used under an orbital protocol. In addition, an intravenous contrast material, gadolinium, can be injected to enhance some pathologic processes. An imaging sequence known as fat suppression is used with gadolinium. With this technique, the normally bright orbital fat appears dark. Without fat suppression, you will not see any enhanced orbital structures against the normally bright fat background.

There are many specific sequences that help with imaging certain disease processes; for example, the FLAIR sequence is especially good for identifying optic neuritis due to demyelinating disease. You will want to develop a working relationship with a radiologist interested in orbital disease to help you with these nuances. Similarly, you will find that working with an interventional radiologist can help you understand and deal with vascular flow issues in some of your orbital patients.

In practice, you will be looking at T1 and T2 scans with contrast injection. Use these tips to evaluate an MRI scan:

MRI has several practical disadvantages compared with CT scanning. MRI is still about three times more expensive than CT. Imaging takes significantly longer. Bone is poorly viewed. As we said above, the spatial resolution of MRI is less than that of CT, so detail is not as clear. MRI is not safe for patients who have metallic foreign bodies or aneurysm clips in place. It is difficult, or impossible, to obtain an MRI scan for any patient who requires a ventilator, pacemaker, or cardiac monitor.

Special imaging studies

Special imaging studies are available or can be arranged with consultation with your radiology colleagues.

CT studies for stereotactic navigation are commonly obtained by our ear, nose, and throat (ENT) and neurosurgical colleagues, especially when performing endoscopic operations. You are probably familiar with studies but, if not, you should see the technique in action. By linking the preoperative high resolution images with cameras in the operating room that sense the position of your instruments, you can have real time localization of your position in the patient. This technique is especially useful where the “normal” anatomy is quite variable (paranasal sinuses) and for reoperations where normal landmarks have been altered. It can be helpful for you when you are operating in less familiar areas. For example, I used this when I was less experienced in skull base procedures. CT scanning before and during Valsalva maneuver is helpful for detecting the venous flood seen in orbital varies. 3D CT scans produce amazing pictures (see Figure 14-9). These images are most useful for craniofacial anomalies and extensive facial trauma. 3D scans are valuable for planning a reconstructive operation and are also useful for teaching residents and patients. CTA and MRA are easy ways to view the blood supply of a tumor. For a number of reasons, MRA is usually the first choice for our purposes. Arteriography remains the gold standard for vascular imaging. At the same time, therapeutic selective occlusion of feeding vessels can cure or decrease vascular flow decreasing or eliminating the problem or, in some cases, making operation safer. Similarly, direct venous puncture and occlusion can be helpful in selected cases of varix or other mixed venous malformations. If your practice includes these patients, you will need a strong working relationship with a neurointerventional radiologist. Echography has been used in the imaging of ocular and orbital diseases for many years. In the hands of experienced practitioners, useful information can be obtained. In most centers, CT and MRI have replaced echography in the study of orbital disease.

Figure 14-9 Orbital teratoma. (A) Extremely rare and large congenital orbital mass in premature infant. (B) 3D CT reconstruction demonstrates soft tissue mass and large bony orbit. (C) Axial CT scan of head, soft tissue window—shows a large heterogeneous mass in the orbit without extension into the brain. Eye appears to be flattened at the most anterior portion of the mass. (D) Sagittal T1 MRI of the head, gadolinium enhanced, shows heterogeneity prompting vascular studies. (E) MR angiogram (MRA) demonstrates prominent vascular flow from the internal carotid artery branches. (F) Carotid angiography confirmed carotid artery flow. (G) Carotid angiography after occlusion of feeding arterial supply. (H) Successful tumor excision (orbital exenteration) with minimal blood loss.

The information that is available with current imaging techniques and the expertise of our radiology colleagues is incredible. This information can be extremely valuable for diagnosis and surgical planning. A good example is Figure 14-9 which focused our attention on the blood supply of a large congenital mass in a newborn. Vascular studies and embolization made the tumor removal safe for this premature baby weighing only 3 pounds.

Goals of imaging

As we have already discussed, many patients with proptosis will undergo imaging studies. Orbital imaging serves two purposes:

Most times with a quick look at the scan, you will be able to get an idea of what is causing the proptosis. Probably you will see one of two situations:

In a few situations, you may be able to make the diagnosis based upon the scan alone. For example, bilateral enlargement of extraocular muscles indicates thyroid orbitopathy until proven otherwise. More likely, the imaging will give you a few possible diagnoses. For example, an enlarged optic nerve usually indicates meningioma or glioma.

If a mass appears separate from the surrounding structures, the characteristics of the mass may help you put the lesion in a particular pathogenic category, such as neoplasm or inflammation. Based on the location of the mass in the orbit, you can determine the best surgical approach for biopsy.

Remember, the questions we are trying to answer are: “What is it?” and “What is the best surgical approach for biopsy?” Some specific characteristics of an orbital mass will help you with the diagnosis and surgical approach:

Location

Imaging clues to the biologic behavior of the mass

Relationship to adjacent soft tissue—a pusher or an eater?

This is important. Does the mass push the adjacent structures aside or does it infiltrate the adjacent tissues? Infiltrative lesions are usually malignant. Well-circumscribed lesions with smooth borders are usually benign (Figure 14-10). Think of these lesions as “pushers” or “eaters.” Pushers are more likely benign. Eaters are more likely malignant. Is the mass pushing against the optic nerve or growing into the optic nerve (Figure 14-11)? The latter lesion is more likely malignant. The relationship to adjacent structures, or borders, gives you a “snapshot in time” estimate of the biologic behavior of the mass. This concept is simple but extremely important.

Figure 14-10 Infiltrative mass compared with well-circumscribed mass. (A) CT scan of infiltrative lesion shown to be a metastatic breast carcinoma. (B) CT scan of a well-circumscribed benign mass, a cavernous hemangioma. Note that the medial orbital wall is bowed outward, but not eroded.

Figure 14-11 MRI scan of intraconal mass, medial to the optic nerve, apparently attached to the nerve. Proven by biopsy to be a metastatic cutaneous melanoma. Smooth shape is not characteristic of most metastatic tumors, which are infiltrative in nature.

Relationship to adjacent bone fossa formation or bone erosion

The relationship of a soft tissue mass to the adjacent bone gives similar information about the biologic behavior of the mass. Slow-growing benign masses “push” the bone or cause fossa formation. Aggressive malignant tumors “eat” the bone or cause bone erosion. When you evaluate a lacrimal gland mass, the presence of fossa formation is typical of a benign slow-growing mixed tumor of the lacrimal gland (Figure 14-12).

Figure 14-12 Orbital bone changes. (A

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