Journal of Neuro-Ophthalmology, December 1995, Volume 15, Issue 4

Incidental Asymptomatic Orbital Calcifications

OBJECTIVE: To use modern computed tomography (CT) imaging to quantify the incidence of asymptomatic incidental orbital calcifications and describe their histological features. MATERIALS AND METHODS: One hundred orbital CT scans were reviewed. In addition, patients who had orbital calcification(s) detected on a brain CT scan were examined by the ophthalmology service. RESULTS: Of the orbital CT scans, 2% had bilateral drusen of the optic nerve head, 3% had calcified scleral plaques anterior to the medial or lateral rectus muscles, and 3% had bilateral ossification of the trochlear apparatus. Routine brain CT scans detected asymptomatic calcifications of the sclera and dura surrounding the proximal optic nerves. CONCLUSION: Incidental asymptomatic orbital calcifications are commonly encountered on modern high-resolution CT images of the brain and orbit. This article should help the clinician to confidently distinguish these densities from foreign bodies or pathological calcifications.

Journal of Neuro- Ophthaimology 15( 4): 203- 203, 1995. © 1995 Lippincott- Raven Publishers, Philadelphia Incidental Asymptomatic Orbital Calcifications Jennifer L. Murray, M. D., L. Anne Hayman, M. D., Rosa A. Tang, M. D., and Jade S. Scniffman, M. D. Abstract: Objective: To use modern computed tomography ( CT) imaging to quantify the incidence of asymptomatic incidental orbital calcifications and describe their histo­logical features. Materials and Methods: One hundred orbital CT scans were reviewed. In addition, patients who had or­bital calcification( s) detected on a brain CT scan were examined by the ophthalmology service. Results: Of the orbital CT scans, 2% had bilateral drusen of the optic nerve head, 3% had calcified scleral plaques anterior to the medial or lateral rectus muscles, and 3% had bilateral ossification of the trochlear appa­ratus. Routine brain CT scans detected asymptomatic calcifications of the sclera and dura surrounding the proximal optic nerves. Conclusion: Incidental asymptomatic orbital calcifica­tions are commonly encountered on modern high-resolution CT images of the brain and orbit. This article should help the clinician to confidently distinguish these densities from foreign bodies or pathological calcifica­tions. Key Words: Computed tomography- Orbit- Cal­cification- Drusen- Trochlear apparatus- Medial/ lateral rectus muscle- Dura ossification- Dura mater. Manuscript received October 22, 1994. From the Department of Ophthalmology, UTMB, Galveston, 0. L. M., R. A. T.), Department of Radiology, Baylor College of Medicine, ( L. A. H.), Department of Ophthalmology, UTMSH, Houston, Texas, and West Palm Beach, Florida ( J. S. S.), U. S. A. Address correspondence and reprint requests to Dr. L. A. Hayman, Department of Radiology, Baylor College of Medi­cine, One Baylor Plaza, Houston, TX 77030, U. S. A. The computed tomographic ( CT) literature that describes orbital calcification is more than a decade old ( 1- 4). Modern high- resolution scanners have greatly improved the sensitivity of this technique, and calcifications in asymptomatic individuals are now routinely seen. These can initiate unwar­ranted concern that a pathological process or for­eign body is present. The purpose of this article is to provide a practical guide to the imaging features of these incidental calcium deposits. It illustrates benign calcifications in the optic nerve head, troch­lear apparatus of the superior oblique muscle, the sclera, and the proximal dural sheath of the optic nerves. MATERIALS AND METHODS The material for this article came from two stud­ies. The first was a retrospective orbital CT study on 100 unselected Ben Taub General Hospital pa­tients who were examined by two authors ( J. M., L. A. H.). Scans with motion artifacts were ex­cluded from consideration. A General Electric 9800 Signa Scanner was used for all cases. Eighty- nine cases had 3- mm axial and coronal views of the or­bits. All of the data were filmed in narrow ( soft tissue) and wide ( bone window) settings. The CT scan slices were angled to avoid dental- filling arti­facts. The scans in the remaining 11 cases had only axial views of the orbit. The incidence of calcification in the optic nerve head, sclera, and trochlear apparatus of the supe­rior oblique muscle was noted. The sex and age of each patient was recorded. The medical charts of all cases with calcifications were reviewed for or­bital or systemic pathological conditions or both. No attempt was made to determine the race of each patient because diversity is the hallmark of our patient population. The second study was a 6- month review of brain CT scans to detect orbital calcifications. Cases in 203 204 /. L, MURRAY ETAL. which calcifications were seen in areas not de­scribed in the orbital study were selectively re­ferred to the ophthalmology clinic for evaluation. RESULTS This retrospective orbital CT study analyzed 199 orbits in 100 patients. One patient had destruction of the right globe by a gunshot blast. The mean age was 35 years; the range was 3 to 85 years old. There were 28 female and 72 male patients in the study. Calcifications were noted in 8% of the pa­tients. Two patients, one female and the other male, had bilateral drusen of the optic nerve head ( Fig. 1). Three patients had bilateral calcifications in the trochlear apparatus of the superior oblique muscle ( Fig. 2A and B). This group contained two FIQ. 1. Axial computed tomography shows bilateral calcification ( arrow­heads) in the substance of the optic nerve head, consistent with the diag­nosis of optic nerve drusens. men ( 30 and 48 years old) and one girl ( 16 years old). None of them had diabetes. Two patients had scleral calcifications, A 65- year- old man had bilateral calcified scleral plaques anterior to the insertion of the lateral rectus muscle ( Fig. 3). An 85- year- old man had a unilateral calci­fication of the sclera medial to the insertion of the medial rectus muscle ( Fig. 4). The review of the brain CT scans demonstrated three patients with orbital calcifications in areas not described in the first orbital survey. There were two women ( 43 and 48 years old) and one man ( 55 years old). Two cases had scleral calcifica­tions ( Figs. 5 and 6). Bilateral calcifications that ap­peared to be in the dural sheath surrounding the proximal optic nerve were seen in one case ( Fig. 7). None of these cases had a history of trauma, in- ( A) W FIG. 2. Coronal ( A) and axial ( B) computed tomography scans show calcification in the cartilaginous portion of the trochlear apparatus of the superior oblique muscle ( arrowheads). / Ueuro- Ophlhalmol Vol, 15, No, 4, 1995 ORBITAL FIG. 3. Axial ( A) and coronal ( B) computed tomogra­phy scans show bilateral calcification in the sclera ( ar­rowheads) just anterior to the insertions of the lateral rectus muscles, consistent with calcified scleral plaques. fection, or eye symptoms. The funduscopic exam­ination was normal in all cases. DISCUSSION Incidental asymptomatic calcification in the orbit occurred in 8% of orbital CT scans reviewed for this article. In spite of the frequency of this find­ing, it has received little attention in the recent literature ( 1^ 4). The following discussion outlines what is known concerning the features of these orbital calcifications. 205 FIG. 4. Axial ( A) and coronal ( B) computed tomogra­phy scans show a unilateral calcification In the sclera just anterior to the insertion of the medial rectus mus­cle, consistent with a calcified scleral plaque. Drusen of the Optic Nerve Head ( Fig. 1) On CT, drusen appears as a discrete, rounded high density confined to the optic disc surface ( Fig. 1). CT scans are so sensitive that they may detect drusen when the ophthalmoscopic examination is apparently normal. Therefore, the incidence of drusen by ophthalmoscopic observation was re­ported as only 0.34% of the population in Den­mark ( 3). In this CT study, it was found in 2% of the heterogeneous population of patients exam­ined at a large county hospital. Drusen of the optic disc was first described in / Netuv- Ophthalmol, Vol. 15, No. 4, 1395 206 /. I. MURRAY ET Al, 1858 ( 5). It is inherited as an irregular dominant trait, primarily in blond whites. It may be referred to as a " hyaline body" of the optic nerve head because it is a calcific cellular accretion of hyaline­like material. It is usually buried within the sub­stance of the nerve head anterior to the lamina cribrosa. It is covered by axons, glia, and the ves­sels that supply the nerve head. It can cause a distortion in the shape of the nerve, which causes the margins of the disc to become blurred or " lumpy," making it difficult to delineate them from the surrounding retina. Thus the drusen can FIG. 6. Axial computed tomography scan of the brain shows a calcification at the insertion of the superior rectus muscle ( arrowhead). FJG. 5. Axial computed tomography of the orbit shows small calcified scleral areas at the insertion of the lateral rectus muscle ( arrowheads). In addition, dense scleral calcifica­tions are present bilateraiiy ( arrows). be confused with disc edema on ophthalmoscopic examination; therefore, a CT may be ordered to rule out a space- occupying lesion. However, B scan ultrasonography is the procedure of choice to detect buried drusen. Retinoblastomas and optic nerve gliomas are among the few lesions that may produce calcification of the posterior globe. Know­ing the differences in radiologic presentation of these three entities is important in differentiating a benign from a more serious cause of pseudo-papilledema ( 1,2). Clinically, 87% of patients with drusen may even develop arcuate visual field de­fects and optic disc hemorrhage ( 3). Trochlear Apparatus Calcification ( Fig. 2) The trochlear apparatus of the orbit is the carti­laginous structure through which the superior ob­lique tendon and its sheath pass. The exact site of calcium deposition has not been determined by an­atomic studies. Possibilities include the tendon of the superior oblique muscle, the synovial sheath, and the cartilage ( 6). In this study, high- resolution CT images clearly showed that the calcifications were in the cartilage ( Fig. 2). A recent CT study suggests that calcification in the trochlear apparatus is strongly associated with diabetes in patients younger than 40 years ( 6). In that study, 12% of patients ( 19 of 159) had calcifi­cation in the trochlea apparatus. Our study found an incidence of only 3% This may be because none of our patients had diabetes, even though two of the three were younger than 40 years. Scleral Plaques ( Figs. 3- 6) Calcification of the sclera has been reported at sites of focal senile thinning that occur anterior to / Neuro- Ophlhalmol, Vol. 25, Wo. i, 1995 ORBITAL CALCIFICATIONS 207 FIG. 7. Axial ( A, B) and coronal ( C) computed tomog­raphy scans show calcification in the medial aspect of the dural sheath ( arrowheads in A and B) surrounding the proximal optic nerves. the tendinous insertions of the medial or lateral rectus muscles ( Figs. 3- 5) ( 7). In this study, focal calcification was also found at the insertion of the superior rectus muscle ( Fig, 5). These areas are commonly seen by the ophthalmologist and were identified in 3% of the orbital CT studies reviewed for this article. Scleral thinning and calcification may be caused by hyaline degeneration or may be secondary to the mechanical stresses created by contraction of the rectus muscles. The frequent occurrence of plaques in the elderly supports this concept. In this study, the youngest patient with scleral calci­fications was 48 years of age. If unilateral scleral calcification could be found in a patient with con­genital contralateral palsy of a rectus muscle, it would supply the evidence needed to substantiate this mechanistic theory. Asymptomatic calcification of the sclera at sites other than muscle attachments can rarely occur ( Fig, 6). Focal calcifications have been noted in the posterior sclera of patients with hyperparathy­roidism, vitamin D intoxication, and milk- alkali syndrome. In these cases, the scleral calcifications tend to be more diffuse and not so localized as those seen at the tendinous insertions ( 1). Dural Ossification ( Fig. 7) The dura mater is composed of fibrous tissue and elastic fibers. Its inner surface consists of me-sothelial cells. Under pathological situations, they can act as fibroblasts. For unknown reasons, these cells may undergo metaplastic change and form bone. These ossified plaques may be found in the dura of the flax, tentorium, and calvaria of 10% of normal individuals. However, this incidence may be increased in patients with endocrine disorders ( 8). In our study, we found a case of bilateral sym­metric ossification in the dural sheath of the optic nerve ( Fig. 7). This is easily distinguished from the unilateral calcification( s) seen in symptomatic pa­tients with meningiomas of the optic nerve sheath or optic nerve glioma. To the best of our knowl­edge, incidental calcification of the dura of the op­tic nerve sheath has not been reported previously in the literature. CONCLUSION A thorough knowledge of the location of phys­iologic orbital calcifications will prevent confusion when orbital CT scans are examined for the possi­bility of a foreign body. In addition, familiarity with these densities allows the imaging clinician to confidently distinguish asymptomatic incidental orbital calcifications from pathological conditions. Acknowledgment: The authors thank the computed tomographic sections of the Ben Taub Radiology Depart­ment for the beautiful images used in this article. REFERENCES 1, Brant- Zawadzki M, Enzmartn D. Orbital computed tomog­raphy: calcific densities of the posterior globe. / Comput Assist Totnogr 1979j3: 503- 5. / Neuro- Ophthdmol, Vol. 15, No. 4, 1995 208 ]. L. MURRAY ET AL. 2. Edwards MK, Bunac JR, Harwood- Nash DC, Optic disk drusen. / Comput Assist Tomogr 1982; 6: 383- 4. 3. Lorentzen SE. Drusen of the optic disc. Acta Ophthalmol { Copenk) 1966;( suppl 90). 4. Hedges TR, Pozzi- Mucelli R, Char DH, et al. 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