lntradiploic Epidermoid Cysts of the Bony Orbit ANTONIUS A. EIJPE, MD/ LEO KOORNNEEF, PhD/ BEN VERBEETEN, Jr., MD/ FRANS L. M. PEETERS, PhD/ FRANS W. ZONNEVELD, PhD,3 JOHANNES BRAS, PhD4
Abstract: Epidermoid cysts originating within the diploic space of the bony orbit are rare. The authors retrospectively studied four patients with an intradiploic epidermoid cyst of the orbital bones to investigate the clinical and the computed tomographic (CT) findings. The clinical presentation was dependent on the location of the slowly expanding epidermoid cyst. The sphenoid bone was involved in three patients and the frontal bone in one patient. Proptosis caused by intraorbital extension of the mass was the most common presenting sign. The findings on high-resolution CT scans appeared to be specific for intradiploic epidermoid cysts. The typical sclerotic margin, which is diagnostic of intradiploic epidermoid cysts, can be demonstrated by CT scans with a bone window setting. Ophthalmology 1991; 98:1737-1743
Intradiploic epidermoid cysts extending into the orbit are an uncommon cause of unilateral proptosis. 1- 5 Approximately 30 cases of epidermoid cysts arising within the orbital bones have been reported. 1- 22 Epidermoid cysts are benign, slow growing tumors. A major problem is their tendency to recur after surgical excision, which should be prevented by a complete removal of the cyst. 9•23 •24 Computed tomography (CT) can be important in the diagnosis and the planning of the surgical approach. A review of the literature revealed only eight case reports of orbital intradiploic epidermoid cysts with CT scans. 15- 22 We describe the clinical and the high-resolution CT findings in 4 patients with orbital intradiploic epidermoid cysts that presented at the Orbital Center over the past 10 years.
CASE REPORTS Case 1. An 18-year-old woman was referred with a recurrent tumor of the left frontal bone. The lesion had first been removed
Originally received: February 11, 1991. Revision accepted: May 8, 1991. 1
Orbital Center, Department of Ophthalmology, University of Amsterdam, The Netherlands. 2 Department of Diagnostic Radiology, University of Amsterdam, The Netherlands. 3 Department of Diagnostic Radiology, University of Utrecht, The Netherlands. 4 Department of Pathology, University of Amsterdam, The Netherlands. Reprint requests to Antonius A. Eijpe, MD, Orbital Center A2-118, Academic Medical Center, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
when she was 12. The histopathologic diagnosis was epidermoid cyst. She had noted a progressive swelling of the left eyebrow over the past 2 years. On examination, visual acuity was 20/20 in both eyes. There was a 2-mm ptosis of the left upper eyelid. A fluctuant mass was felt just above the left eyebrow. There was no proptosis. Computed tomographic scans demonstrated a well-circumscribed soft-tissue mass in the diploe of the left frontal bone involving the superotemporal orbital quadrant (Fig 1). The inner and outer table of the frontal bone were partially destroyed and extension of the mass into the orbit and the anterior cranial fossa was seen (Fig IC). The bone surrounding the lesion showed a distinct sclerotic margin on a bone window setting (Figs I B, C). Viewing console analysis of the scans revealed a mean attenuation value of the mass of 29 Hounsfield units (HU). A recurrence of the epidermoid cyst was suspected and an anterior orbitotomy combined with a direct approach via the bone defect (caused by previous surgery) in the frontal bone was performed. A cystic mass containing cheese-like material was found. There was erosion of the orbital roof and the lesion was attached to the dura. After dissection of the cyst wall, a small tear in the dura was repaired with fascia lata. The lesion was completely removed. Results of histopathologic examination showed a squamous epithelial cyst wall and desquamated layers of keratin toward the center of the cyst (Fig 2). This confirmed the diagnosis of an epidermoid cyst. Postoperatively, the swelling in the brow region and the ptosis had resolved. Three years after surgery, she complained of pain in extreme left and upgaze. However, CT revealed no signs of regrowth of the epidermoid cyst. She has had no recurrence during a follow-up of 8 years. Case 2. A 23-year-old woman presented with a 6-year history of painless unilateral proptosis. She complained of progressive protrusion of her left eye with increasing double vision over the previous 4 months.
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Ocular examination revealed a visual acuity of 20/20 in each eye. There was a left upper eyelid ptosis of 2 mm. Exophthalmometry demonstrated 8 mm of proptosis with 2 mm of hypoophthalmia of the left eye. Ocular motility was slightly restricted in extreme left and upgaze. Computed tomographic scans showed a well-defined, homogeneous soft-tissue mass, with a density similar to the brain, in the diploe of the sphenoid bone. This was associated with a partial defect in the lateral orbital wall and extension of the mass into the orbit (Fig 3A). There was displacement of the lateral rectus muscle and the left globe. Extension of the lesion into the medial cranial fossa was also noted (Fig 3C). A bone window setting demonstrated a sclerotic margin surrounding the lesion in the sphenoid bone (Figs 3B, C). The mean density of the lesion was 33 HU. A left lateral orbitotomy was performed exposing a large mass (3 X 4 em) attached to the sphenoid bone. The lesion extended into the adjacent parts of the lateral orbital wall and into the medial cranial fossa. After careful dissection, a cystic mass containing white waxy material was completely removed without damage to the dura. The histopathologic diagnosis was that of an epidermoid cyst. Postoperatively, the patient has done well with retention of normal vision, no residual globe displacement and with normal ocular motility. During a follow-up of 4 years there were no clinical signs of recurrence. A follow-up CT scan revealed no signs of regrowth of the lesion two years after surgery (Fig 3D). Case 3. A 52-year-old man had a 4-year history of painless unilateral proptosis. At presentation, he complained of progressive displacement of his left globe. He had also noted the proptosis to be intermittent when chewing. Ocular examination revealed a best corrected visual acuity of 6/9 in both eyes. There was 4 mm of proptosis on the left. Chewing resulted in a 2- to 3-mm increase and decrease of the proptosis. Ocular motility was not affected. A mild cataract was seen on the right and an advanced cataract on the left. Computed tomography showed a large soft-tissue mass, with a density comparable with the brain, centered in the left sphenoid bone. A full defect in the lateral orbital wall had resulted in a communication with the temporalis fossa and the medial cranial fossa (Fig 4). The bone window setting demonstrated sclerotic margins in the defect of the sphenoid bone adjacent to the mass (Fig 4B). The mean attenuation value of the mass was 33 HU. An extended eyebrow incision was performed and a defect of the lateral orbital wall was seen. A cystic mass extended into the infratemporal fossa, the pterygopalatine fossa, the orbit, and into the medial cranial fossa, exposing the dura. The cyst was radically removed without damage to the dura. Results of histopathologic examination showed a keratinizing squamous epithelial lining with evidence of a chronic inflammatory reaction. The diagnosis was that of an epidermoid cyst. Postoperatively, the proptosis had disappeared. He had a limitation of adduction of the left eye, which resolved within 2 months. One year later, chewing did not alter the position of the left eye. During a follow-up period of 4 years there was no recurrence.
Fig 1. Case I. Top, coronal CT scan demonstrates a well-circumscribed soft-tissue mass in the diploe of the left frontal bone. Notice the defect in the lateral aspect of the frontal bone as a result of previous surgery (arrow). Center, bone window CT scan shows a sclerotic margin in the bone surrounding the lesion (arrow). Bottom, bone window CT scan demonstrates the extension of the mass into the orbit and the anterior cranial fossa. Notice also the sclerotic margin in the bone (arrowhead).
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c Fig 2. Case I. Microscopic slide of epidermoid cyst shows a lining of squamous epithelium with desquamated layers of keratin toward the center (C) of the cyst (hematoxylin-eosin; original magnification, X40).
Case 4. A 26-year-old woman was referred with a recurrent tumor in the right temporalis fossa. At the ages of 10, 15, and 16 years, she was operated on for removal of an epidermoid cyst. After the third operation she was asymptomatic for I0 years. She presented with a 3-month history of a "feeling of pressure" in the right orbit. Results of ocular examination showed a visual acuity of 20/20 in both eyes. A right proptosis of2 mm was found. Ocular motility was normal. Computed tomographic scans demonstrated a well-circumscribed mass in the right temporalis fossa (Fig SA). Bone defects were seen in the lateral orbital wall and the temporal bone, probably as a result of previous surgery. The average central density of the mass was 16 HU. A fourth recurrence was suspected and surgery with participation of a neurosurgeon was planned. A right modified hairline incision was performed. After careful dissection of the anterior cranial part of the temporalis muscle, a large mass was found in the temporalis fossa. It was-not possible to remove the cyst completely because the cyst wall was firmly adherent to the dura. The histopathologic diagnosis was epidermoid cyst. The postoperative course was uneventful, but 18 months later, symptoms returned and CT scans confirmed a recurrence (Fig SB). It was decided to postpone surgery because she had only minor complaints.
DISCUSSION Epidermoid cysts arising within the bony wall of the orbit are extremely rare. Epidermoid tumors are inclusions of ectodermal elements in sites not normally containing these structures. 25 They can be divided into primary or secondary lesions. Primary or congenital epidermoid cysts are related to implantation of ectoderm at time of closure
of the neural groove, or of other epithelial fusion lines. Secondary or acquired epidermoid cysts are usually caused by post-traumatic inclusion of surface epithelium. 26 The term "dermoid" has been used to describe both dermoid cysts and epidermoid cysts. However, both histopathologically and clinically, epidermoid cysts can be distinguished from dermoid cysts. 3•4•19 Epidermoid cysts consist of ectodermal derivatives only. In dermoid cysts, the cyst wall is composed of ectodermal plus mesodermal structures such as hair follicles and sebaceous glands. Dermoid cysts are usually discovered in childhood or young adolescence. Generally, epidermoids present later in life because they are located deeper in the orbit, frequently grow within the diploe of the bone, and remain latent for longer periods. 4 •19 In 1838, Muller was the first to describe an intradiploic epidermoid cyst. He introduced the term "cholesteatoma" because of the presence of cholesterol crystals in the lesion. Most authors believe this is a misnomer because it does 24 not really describe the nature of the tumor. 3.4·8·21- ·27·28 Because cholesterol crystals can also be found in other lesions and are not a consistent finding in epidermoid cysts, the name "cholesteatoma" should be avoided. Intradiploic epidermoid cysts can be located in any part of the skull.9 They are derived from ectodermal remnants that stay within the cranial bones during embryonic development.25·27 The lateral orbital region is a common site for epidermoid cysts. 10•14 In three of our patients, the epidermoid cyst was originating in the diploic space of the lateral orbital wall and in one patient in the lateral part of the frontal bone. The optic vesicles develop in about the fifth week of intrauterine life and it is probable 1739
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Fig 3. Case 2. A, axial CT scan demonstrates a homogeneous soft-tissue mass in the left sphenoid bone. Notice the extension of the mass, with density comparable with the brain, into the orbit with displacement of the lateral rectus muscle and the left globe. B, bone window setting shows a distinct sclerotic rim in the adjacent diploic bone (arrow). C, axial CT scan with bone window setting demonstrates extension of the lesion into the medial cranial fossa. Notice the sclerotic bone margin (arrowhead). D, axial follow-up scan 2 years after surgery with bone window setting demonstrates formation of new bone (arrow) and the defect in the bone caused by the lateral orbitotomy (arrowhead).
that misplaced cell rests associated with these vesicles may give rise to laterally located epidermoid tumors. 29 Intradiploic epidermoid cysts of the orbit are associated with a variety of symptoms that correlate with the location of the tumor. The most common presenting sign is unilateral proptosis, which is caused by long-term pressure of the cyst extending into the orbit. I-s It may be accompanied by impairment of extraocular movements, dip1740
lopia, and, occasionally, blurring of visionY Facial deformity can be seen also in cases without intraorbital extension. Although headache is reported in patients with intracranial extension of diploic epidermoid cysts, they rarely produce significant neurologic signs. 8 · 18 •28 This is probably due to the very slow enlargement of the epithelial cysts. The proptosis in our third patient was remarkable in
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Fig 4. Case 3. A, coronal CT scan shows a large mass, with a density similar to brain, in the left superotemporal orbital quadrant. Notice the destruction of the lateral orbital wall resulting in a communication with the temporalis fossa. B, axial CT scan with bone window setting demonstrates sclerotic margin in the sphenoid bone adjacent to the mass (arrow) and a bowing of the lateral orbital wall caused by pressure of the lesion (arrowhead).
that it occurred intermittently with mastication. This phenomenon can be explained by mechanical compression of the orbital contents by the tumor mass caused by the contractions of the temporalis muscle through the defect in the lateral orbital wall. This "mastication proptosis" was earlier described in a patient with Graves disease after
orbital decompression and in two patients with dermoid cysts and bone defects in the lateral orbital wall. 30•31 The typical radiologic appearance of an intradiploic epidermoid cyst is a bone defect with smooth demarcated edges associated with thickened sclerotic margins. 3•4•10 •23 •24 •26 •32 This sclerotic margin is caused by the
Fig 5. Case 4. A, axial CT scan demonstrates a well-circumscribed soft-tissue mass in the right temporalis fossa. This was a fourth recurrence of a epidermoid cyst. Notice the defects in the lateral orbital wall and the right temporal bone as a result of previous surgery. B, axial follow-up CT scan shows a mass suggestive of a fifth recurrence of the epidermoid cyst.
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slow, steady prolonged pressure exerted by the tumor on the bone. 33 •34 At the present time, CT is one of the first investigations in patients with intraorbital masses. On CT scans, orbital diploic epidermoid cysts are usually well-defined soft-tissue masses with a density comparable with brain parenchyma, 16 •19•21 •22 as was seen in all except our last patient. The attenuation values in our first three patients varied from 29 to 33 HU, which is in the range of brain tissue. Occasionally, slightly lower attenuation values can be found in diploic epidermoid cysts. This is thought to be due to degeneration of keratin and the presence of cholesterol crystals. 35 The characteristic bone defects, as seen on plain radiographs, can be clearly visualized on CT scans. In this study, bone window CT scans demonstrated the sclerotic margin of the bone surrounding the epidermoid cysts. The radiologic differential diagnosis includes all lytic defects in the diploe such as eosinophilic granuloma, cystic angioma, osteoid osteoma, and cholesterol granuloma. 34•36 These lesions, however, are not accompanied by a sharp bony edge and the typical sclerotic margin. 33 •37 Recently, Fukuta and Jackson 22 reported bone window CT images in a patient with an orbital intradiploic epidermoid cyst. They also described a patient with a cholesterol granuloma but were unable to differentiate between these lesions on CT scans, both being isodense with brain. Unfortunately, they did not show bone window CT images in the latter patient. The absence of the sclerotic margin is characteristic of a cholesterol granuloma and would have differentiated between these lesions. 37 We recommend the use of bone window CT images in every case of an orbital mass with bone involvement. Although the intraorbital extension of epidermoid cysts is easily seen on CT scans, it can be difficult to distinguish the intracranial part of these lesions from brain. Fukuta and Jackson 22 have shown that magnetic resonance imaging and CT are complementary in the evaluation of epidermoid cysts. Magnetic resonance imaging lacks the bony details of CT, but it allows the appreciation of the intracranial extension of the epidermoid because of signal differences between the tumor and the brain. Epidermoid cysts should be excised with great care. Intradiploic epidermoid cysts extended intracranially in all our patients. Neurosurgical participation is recommended in such cases because of the close relation of the cyst with the dura. Although all patients were operated on by our orbital surgeon (LK), a neurosurgeon was on stand by in all cases and assisted with surgery on our fourth patient. The epithelial lining of these cysts should be completely removed to prevent recurrences. 9 •23 •24 Parke et al 5 reported 28% of recurrences in a review of 13 cases of orbital epidermoid cysts in the literature. It can take up to 30 years for an epidermoid cyst to recur. 13 In this study, our first 3 patients are free of recurrences after 4 to 8 years, but, in patient 4, a regrowth occurred within 18 months after the fourth operation. Occasionally, epidermoid cysts are difficult to remove from the dura, 8 as was the problem with this patient. Certainly, the epidermoid cyst must be excised again and if the dura is damaged it should be 1742
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repaired primarily or with a fascia graft 14 of the fascia lata, the temporalis fascia, or with other dura substitutes. Mild dessicating diathermy is advocated to destroy any tags of epithelium in cases whereby a good resection of tissue is not possible. 4 Malignant change can occur in the epithelial lining of intradiploic epidermoid cysts. Yanai et al 38 reported 5 cases with malignant transformation out of a series of about 100 intradiploic epidermoid cysts collected from the literature. It seems that epidermoid cysts that have undergone several operations and repeated inflammations are susceptible to cancer formation. 13 •38 •39 In conclusion, the diagnosis of orbital intradiploic epidermoid cysts is greatly aided by high-resolution CT scans, especially with bone window settings. Complete excision is required to prevent recurrence with the potential for subsequent malignant transformation.
REFERENCES 1. Thornhill EH, Anderson B. Extradural diploic epiderrnoids producing unilateral exophthalmos. Arn J Ophthalrnol1944; 27:477-83. 2. Givner I, Wigderson H. Cranial epidermoid with erosion of the roof of the orbit. Report of a case. Arch Ophthalrnol 1948; 39:300-4. 3. Carey PC. Epidermoid and dermoid tumours of the orbit. Br J Ophthalrnol 1958; 42:225-39. 4. Henderson JW ed, Orbital Tumors, 2nd ed. New York: BC Decker, 1980; 75-84. 5. Parke DW II, Font RL, Boniuk M, McCrary JA Ill. 'Cholesteatoma' of the orbit. Arch Ophthalrnol 1982; 100:612-16. 6. Constans GM. Cholesteatoma of the orbit. Arch Ophthalrnol 1943; 30:236-46. 7. Pfeiffer RL, Nicholl RJ. Dermoid and epidermoid tumors of the orbit. Arch Ophthalrnol1948; 40:639-64. 8. Thacker EA. Epidermoid tumors of the frontal bone, sinus and orbit. Arch Otolaryngol 1950; 51 :400-13. 9. Skandalakis JE, Godwin JT, Mabon RF. Epidermoid cyst of the skull. Report of four cases and review of the literature. Surgery 1958; 43: 990-1001. 10. Lee KF, Hodes PJ, Greenberg L, Sinotti A. Three rare causes of unilateral exophthalmos. Radiology 1968; 90:1009-15. 11. Osborn DA, Wallace M. Carcinoma of the frontal sinus associated with epidermoid cholesteatoma. J Laryngol Otol1967; 81:1921-32. 12. Calcaterra TC, Schwartz HE. Cholesteatoma of the frontal sinus. Trans Arn Acad Ophthalrnol Otolaryngol1976; 82:579-81. 13. Holt GR, Holt JE, Davis WE. Late recurrence of a frontal sinus cholesteatoma. Ann Otol Rhinol Laryngol1977; 86:852-5. 14. Campanella RS, Caldarelli DD, Friedberg SA. Cholesteatoma of the frontal and ethmoid areas. Ann Otol Rhinol Laryngol 1979; 88:51823. 15. Lepori JC, George JL, Gdal-on M, Reny A. Kyste epiderrnoide orbitraire de l'adulte. Abord transconjonctival. Rev Otoneuroophtalrnol 1982; 54:159-63. 16. Wakai S. lntradiploic epidermoid turn or of the lateral orbital wall-case report. Neurol Med Chir (Tokyo) 1983; 23:577-9. 17. Guiard JM, Kien P, Colornbani S, Caille JM. lntradiploic epidermoid cysts in adults. CT contribution to diagnosis in 6 new cases. J Neuroradiol 1986; 13:22-31. 18. White AK, Jenkins HA, Coker NJ. lntradiploic epidermoid cyst of the sphenoid wing. Arch Otolaryngol Head Neck Surg 1987; 113:995-9. 19. Lane CM, Ehrlich WW, Wright JE. Orbital dermoid cyst. Eye 1987; 1: 504-11.
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20. Baker RS, Goldstein SJ, Young LW, Wood BP. Radiological case of the month. Epidermoid cyst of the orbit. Am J Dis Child 1988; 142: 979-80. 21. Chowdury CR. Wood CM, Samuel PR, Richardson J. Frontal bone epidermoid-a rare cause of proptosis. Br J Ophthalmol 1990, 74: 445-6. 22. Fukuta K, Jackson IT. Epidermoid cyst and cholesterol granuloma of the orbit. Br J Plast Surg 1990; 43:521-7. 23. Cushing H. A large epidermal cholesteatoma of the parietotemporal region deforming the left hemisphere without cerebral symptoms. Surg Gynecol Obstet 1922; 34:557-66. 24. Rand CW, Reeves DL. Dermoid and epidermoid tumors (cholesteatomas) of the central nervous system. Report of twenty-three cases. Arch Surg 1943; 46:350-76. 25. Toglia JU, Netsky MG. Alexander E Jr. Epithelial (epidermoid) tumors of the cranium: their common nature and pathogenesis. J Neurosurg 1965; 23:384-93. 26. Pear BL. Epidermoid and dermoid sequestration cysts. AJR Am J Roentgenol 1970; 110:148-55. 27. Rowbotham GF. Epidermoids arising in the diploe of the bones of the skull. Br J Surg 1939; 26:506-14. 28. Bucy PC. lntradiploic epidermoid (cholesteatoma) of the skull. Arch Surg 1935; 31:190-9. 29. Fleming JFR, Botterell EH. Cranial dermoid and epidermoid tumors. Surg Gynecol Obstet 1959; 109:403-11 .
30. Bullock JD, Bartley GB. Dynamic proptosis. Am J Ophthalmol1986; 102:104-10. 31. Whitney CE, Leone CR Jr, Kincaid MC. Proptosis with mastication: an unusual presentation of an orbital dermoid cyst. Ophthalmic Surg 1986; 17:295-8. 32. Nager GT. Epidermoids involving the temporal bone: clinical radiological and pathological aspects. Laryngoscope 1975; 85(Pt. 2, Suppl 2):1-21. 33. Haessly M, Lagier R. Anatomico-radiological study of intraosseous epidermoid cysts. ROFO 1982; 137:48-54. 34. Peeters FLM. Die Differentialdiagnose benigner, solitarer Defekte im Schadeldach. Fortschr Geb Rontgenstr Nuklearmed 1972; 117:625-
9. 35. Constans JP, Meder JF, De Divitiis E, et al. Giant intradiploic epidermoid cyst of the skull. Report of two cases. J Neurosurg 1985; 62:445-8. 36. Holthusen W, Lassrich MA, Steiner C. Epidermoids and dermoids of the calvarian bones in early childhood: their behavior in the growing skull. Pediatr Radiol1983; 13:189-94. 37. Eijpe AA, Koornneef L, Verbeeten B Jr, et al. Cholesterol granuloma of the frontal bone: CT diagnosis. J Comput Assist Tomogr 1990; 14: 914-7. 38. Yanai Y, Tsuji R, Ohmori S. et al. Malignant change in an intradiploic epidermoid: report of a case and review of the literature. Neurosurgery 1985; 16:252-6. 39. Haig PV. Primary epidermoids of the skull: including a case with malignant change. AJR Am J Roentgenol1956; 76:1076-80.
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Abstract: Epidermoid cysts originating within the diploic space of the bony orbit are rare. The authors retrospectively studied four patients with an intradiploic epidermoid cyst of the orbital bones to investigate the clinical and the computed tomographic (CT) findings. The clinical presentation was dependent on the location of the slowly expanding epidermoid cyst. The sphenoid bone was involved in three patients and the frontal bone in one patient. Proptosis caused by intraorbital extension of the mass was the most common presenting sign. The findings on high-resolution CT scans appeared to be specific for intradiploic epidermoid cysts. The typical sclerotic margin, which is diagnostic of intradiploic epidermoid cysts, can be demonstrated by CT scans with a bone window setting. Ophthalmology 1991; 98:1737-1743
Intradiploic epidermoid cysts extending into the orbit are an uncommon cause of unilateral proptosis. 1- 5 Approximately 30 cases of epidermoid cysts arising within the orbital bones have been reported. 1- 22 Epidermoid cysts are benign, slow growing tumors. A major problem is their tendency to recur after surgical excision, which should be prevented by a complete removal of the cyst. 9•23 •24 Computed tomography (CT) can be important in the diagnosis and the planning of the surgical approach. A review of the literature revealed only eight case reports of orbital intradiploic epidermoid cysts with CT scans. 15- 22 We describe the clinical and the high-resolution CT findings in 4 patients with orbital intradiploic epidermoid cysts that presented at the Orbital Center over the past 10 years.
CASE REPORTS Case 1. An 18-year-old woman was referred with a recurrent tumor of the left frontal bone. The lesion had first been removed
Originally received: February 11, 1991. Revision accepted: May 8, 1991. 1
Orbital Center, Department of Ophthalmology, University of Amsterdam, The Netherlands. 2 Department of Diagnostic Radiology, University of Amsterdam, The Netherlands. 3 Department of Diagnostic Radiology, University of Utrecht, The Netherlands. 4 Department of Pathology, University of Amsterdam, The Netherlands. Reprint requests to Antonius A. Eijpe, MD, Orbital Center A2-118, Academic Medical Center, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
when she was 12. The histopathologic diagnosis was epidermoid cyst. She had noted a progressive swelling of the left eyebrow over the past 2 years. On examination, visual acuity was 20/20 in both eyes. There was a 2-mm ptosis of the left upper eyelid. A fluctuant mass was felt just above the left eyebrow. There was no proptosis. Computed tomographic scans demonstrated a well-circumscribed soft-tissue mass in the diploe of the left frontal bone involving the superotemporal orbital quadrant (Fig 1). The inner and outer table of the frontal bone were partially destroyed and extension of the mass into the orbit and the anterior cranial fossa was seen (Fig IC). The bone surrounding the lesion showed a distinct sclerotic margin on a bone window setting (Figs I B, C). Viewing console analysis of the scans revealed a mean attenuation value of the mass of 29 Hounsfield units (HU). A recurrence of the epidermoid cyst was suspected and an anterior orbitotomy combined with a direct approach via the bone defect (caused by previous surgery) in the frontal bone was performed. A cystic mass containing cheese-like material was found. There was erosion of the orbital roof and the lesion was attached to the dura. After dissection of the cyst wall, a small tear in the dura was repaired with fascia lata. The lesion was completely removed. Results of histopathologic examination showed a squamous epithelial cyst wall and desquamated layers of keratin toward the center of the cyst (Fig 2). This confirmed the diagnosis of an epidermoid cyst. Postoperatively, the swelling in the brow region and the ptosis had resolved. Three years after surgery, she complained of pain in extreme left and upgaze. However, CT revealed no signs of regrowth of the epidermoid cyst. She has had no recurrence during a follow-up of 8 years. Case 2. A 23-year-old woman presented with a 6-year history of painless unilateral proptosis. She complained of progressive protrusion of her left eye with increasing double vision over the previous 4 months.
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Ocular examination revealed a visual acuity of 20/20 in each eye. There was a left upper eyelid ptosis of 2 mm. Exophthalmometry demonstrated 8 mm of proptosis with 2 mm of hypoophthalmia of the left eye. Ocular motility was slightly restricted in extreme left and upgaze. Computed tomographic scans showed a well-defined, homogeneous soft-tissue mass, with a density similar to the brain, in the diploe of the sphenoid bone. This was associated with a partial defect in the lateral orbital wall and extension of the mass into the orbit (Fig 3A). There was displacement of the lateral rectus muscle and the left globe. Extension of the lesion into the medial cranial fossa was also noted (Fig 3C). A bone window setting demonstrated a sclerotic margin surrounding the lesion in the sphenoid bone (Figs 3B, C). The mean density of the lesion was 33 HU. A left lateral orbitotomy was performed exposing a large mass (3 X 4 em) attached to the sphenoid bone. The lesion extended into the adjacent parts of the lateral orbital wall and into the medial cranial fossa. After careful dissection, a cystic mass containing white waxy material was completely removed without damage to the dura. The histopathologic diagnosis was that of an epidermoid cyst. Postoperatively, the patient has done well with retention of normal vision, no residual globe displacement and with normal ocular motility. During a follow-up of 4 years there were no clinical signs of recurrence. A follow-up CT scan revealed no signs of regrowth of the lesion two years after surgery (Fig 3D). Case 3. A 52-year-old man had a 4-year history of painless unilateral proptosis. At presentation, he complained of progressive displacement of his left globe. He had also noted the proptosis to be intermittent when chewing. Ocular examination revealed a best corrected visual acuity of 6/9 in both eyes. There was 4 mm of proptosis on the left. Chewing resulted in a 2- to 3-mm increase and decrease of the proptosis. Ocular motility was not affected. A mild cataract was seen on the right and an advanced cataract on the left. Computed tomography showed a large soft-tissue mass, with a density comparable with the brain, centered in the left sphenoid bone. A full defect in the lateral orbital wall had resulted in a communication with the temporalis fossa and the medial cranial fossa (Fig 4). The bone window setting demonstrated sclerotic margins in the defect of the sphenoid bone adjacent to the mass (Fig 4B). The mean attenuation value of the mass was 33 HU. An extended eyebrow incision was performed and a defect of the lateral orbital wall was seen. A cystic mass extended into the infratemporal fossa, the pterygopalatine fossa, the orbit, and into the medial cranial fossa, exposing the dura. The cyst was radically removed without damage to the dura. Results of histopathologic examination showed a keratinizing squamous epithelial lining with evidence of a chronic inflammatory reaction. The diagnosis was that of an epidermoid cyst. Postoperatively, the proptosis had disappeared. He had a limitation of adduction of the left eye, which resolved within 2 months. One year later, chewing did not alter the position of the left eye. During a follow-up period of 4 years there was no recurrence.
Fig 1. Case I. Top, coronal CT scan demonstrates a well-circumscribed soft-tissue mass in the diploe of the left frontal bone. Notice the defect in the lateral aspect of the frontal bone as a result of previous surgery (arrow). Center, bone window CT scan shows a sclerotic margin in the bone surrounding the lesion (arrow). Bottom, bone window CT scan demonstrates the extension of the mass into the orbit and the anterior cranial fossa. Notice also the sclerotic margin in the bone (arrowhead).
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c Fig 2. Case I. Microscopic slide of epidermoid cyst shows a lining of squamous epithelium with desquamated layers of keratin toward the center (C) of the cyst (hematoxylin-eosin; original magnification, X40).
Case 4. A 26-year-old woman was referred with a recurrent tumor in the right temporalis fossa. At the ages of 10, 15, and 16 years, she was operated on for removal of an epidermoid cyst. After the third operation she was asymptomatic for I0 years. She presented with a 3-month history of a "feeling of pressure" in the right orbit. Results of ocular examination showed a visual acuity of 20/20 in both eyes. A right proptosis of2 mm was found. Ocular motility was normal. Computed tomographic scans demonstrated a well-circumscribed mass in the right temporalis fossa (Fig SA). Bone defects were seen in the lateral orbital wall and the temporal bone, probably as a result of previous surgery. The average central density of the mass was 16 HU. A fourth recurrence was suspected and surgery with participation of a neurosurgeon was planned. A right modified hairline incision was performed. After careful dissection of the anterior cranial part of the temporalis muscle, a large mass was found in the temporalis fossa. It was-not possible to remove the cyst completely because the cyst wall was firmly adherent to the dura. The histopathologic diagnosis was epidermoid cyst. The postoperative course was uneventful, but 18 months later, symptoms returned and CT scans confirmed a recurrence (Fig SB). It was decided to postpone surgery because she had only minor complaints.
DISCUSSION Epidermoid cysts arising within the bony wall of the orbit are extremely rare. Epidermoid tumors are inclusions of ectodermal elements in sites not normally containing these structures. 25 They can be divided into primary or secondary lesions. Primary or congenital epidermoid cysts are related to implantation of ectoderm at time of closure
of the neural groove, or of other epithelial fusion lines. Secondary or acquired epidermoid cysts are usually caused by post-traumatic inclusion of surface epithelium. 26 The term "dermoid" has been used to describe both dermoid cysts and epidermoid cysts. However, both histopathologically and clinically, epidermoid cysts can be distinguished from dermoid cysts. 3•4•19 Epidermoid cysts consist of ectodermal derivatives only. In dermoid cysts, the cyst wall is composed of ectodermal plus mesodermal structures such as hair follicles and sebaceous glands. Dermoid cysts are usually discovered in childhood or young adolescence. Generally, epidermoids present later in life because they are located deeper in the orbit, frequently grow within the diploe of the bone, and remain latent for longer periods. 4 •19 In 1838, Muller was the first to describe an intradiploic epidermoid cyst. He introduced the term "cholesteatoma" because of the presence of cholesterol crystals in the lesion. Most authors believe this is a misnomer because it does 24 not really describe the nature of the tumor. 3.4·8·21- ·27·28 Because cholesterol crystals can also be found in other lesions and are not a consistent finding in epidermoid cysts, the name "cholesteatoma" should be avoided. Intradiploic epidermoid cysts can be located in any part of the skull.9 They are derived from ectodermal remnants that stay within the cranial bones during embryonic development.25·27 The lateral orbital region is a common site for epidermoid cysts. 10•14 In three of our patients, the epidermoid cyst was originating in the diploic space of the lateral orbital wall and in one patient in the lateral part of the frontal bone. The optic vesicles develop in about the fifth week of intrauterine life and it is probable 1739
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Fig 3. Case 2. A, axial CT scan demonstrates a homogeneous soft-tissue mass in the left sphenoid bone. Notice the extension of the mass, with density comparable with the brain, into the orbit with displacement of the lateral rectus muscle and the left globe. B, bone window setting shows a distinct sclerotic rim in the adjacent diploic bone (arrow). C, axial CT scan with bone window setting demonstrates extension of the lesion into the medial cranial fossa. Notice the sclerotic bone margin (arrowhead). D, axial follow-up scan 2 years after surgery with bone window setting demonstrates formation of new bone (arrow) and the defect in the bone caused by the lateral orbitotomy (arrowhead).
that misplaced cell rests associated with these vesicles may give rise to laterally located epidermoid tumors. 29 Intradiploic epidermoid cysts of the orbit are associated with a variety of symptoms that correlate with the location of the tumor. The most common presenting sign is unilateral proptosis, which is caused by long-term pressure of the cyst extending into the orbit. I-s It may be accompanied by impairment of extraocular movements, dip1740
lopia, and, occasionally, blurring of visionY Facial deformity can be seen also in cases without intraorbital extension. Although headache is reported in patients with intracranial extension of diploic epidermoid cysts, they rarely produce significant neurologic signs. 8 · 18 •28 This is probably due to the very slow enlargement of the epithelial cysts. The proptosis in our third patient was remarkable in
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Fig 4. Case 3. A, coronal CT scan shows a large mass, with a density similar to brain, in the left superotemporal orbital quadrant. Notice the destruction of the lateral orbital wall resulting in a communication with the temporalis fossa. B, axial CT scan with bone window setting demonstrates sclerotic margin in the sphenoid bone adjacent to the mass (arrow) and a bowing of the lateral orbital wall caused by pressure of the lesion (arrowhead).
that it occurred intermittently with mastication. This phenomenon can be explained by mechanical compression of the orbital contents by the tumor mass caused by the contractions of the temporalis muscle through the defect in the lateral orbital wall. This "mastication proptosis" was earlier described in a patient with Graves disease after
orbital decompression and in two patients with dermoid cysts and bone defects in the lateral orbital wall. 30•31 The typical radiologic appearance of an intradiploic epidermoid cyst is a bone defect with smooth demarcated edges associated with thickened sclerotic margins. 3•4•10 •23 •24 •26 •32 This sclerotic margin is caused by the
Fig 5. Case 4. A, axial CT scan demonstrates a well-circumscribed soft-tissue mass in the right temporalis fossa. This was a fourth recurrence of a epidermoid cyst. Notice the defects in the lateral orbital wall and the right temporal bone as a result of previous surgery. B, axial follow-up CT scan shows a mass suggestive of a fifth recurrence of the epidermoid cyst.
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slow, steady prolonged pressure exerted by the tumor on the bone. 33 •34 At the present time, CT is one of the first investigations in patients with intraorbital masses. On CT scans, orbital diploic epidermoid cysts are usually well-defined soft-tissue masses with a density comparable with brain parenchyma, 16 •19•21 •22 as was seen in all except our last patient. The attenuation values in our first three patients varied from 29 to 33 HU, which is in the range of brain tissue. Occasionally, slightly lower attenuation values can be found in diploic epidermoid cysts. This is thought to be due to degeneration of keratin and the presence of cholesterol crystals. 35 The characteristic bone defects, as seen on plain radiographs, can be clearly visualized on CT scans. In this study, bone window CT scans demonstrated the sclerotic margin of the bone surrounding the epidermoid cysts. The radiologic differential diagnosis includes all lytic defects in the diploe such as eosinophilic granuloma, cystic angioma, osteoid osteoma, and cholesterol granuloma. 34•36 These lesions, however, are not accompanied by a sharp bony edge and the typical sclerotic margin. 33 •37 Recently, Fukuta and Jackson 22 reported bone window CT images in a patient with an orbital intradiploic epidermoid cyst. They also described a patient with a cholesterol granuloma but were unable to differentiate between these lesions on CT scans, both being isodense with brain. Unfortunately, they did not show bone window CT images in the latter patient. The absence of the sclerotic margin is characteristic of a cholesterol granuloma and would have differentiated between these lesions. 37 We recommend the use of bone window CT images in every case of an orbital mass with bone involvement. Although the intraorbital extension of epidermoid cysts is easily seen on CT scans, it can be difficult to distinguish the intracranial part of these lesions from brain. Fukuta and Jackson 22 have shown that magnetic resonance imaging and CT are complementary in the evaluation of epidermoid cysts. Magnetic resonance imaging lacks the bony details of CT, but it allows the appreciation of the intracranial extension of the epidermoid because of signal differences between the tumor and the brain. Epidermoid cysts should be excised with great care. Intradiploic epidermoid cysts extended intracranially in all our patients. Neurosurgical participation is recommended in such cases because of the close relation of the cyst with the dura. Although all patients were operated on by our orbital surgeon (LK), a neurosurgeon was on stand by in all cases and assisted with surgery on our fourth patient. The epithelial lining of these cysts should be completely removed to prevent recurrences. 9 •23 •24 Parke et al 5 reported 28% of recurrences in a review of 13 cases of orbital epidermoid cysts in the literature. It can take up to 30 years for an epidermoid cyst to recur. 13 In this study, our first 3 patients are free of recurrences after 4 to 8 years, but, in patient 4, a regrowth occurred within 18 months after the fourth operation. Occasionally, epidermoid cysts are difficult to remove from the dura, 8 as was the problem with this patient. Certainly, the epidermoid cyst must be excised again and if the dura is damaged it should be 1742
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repaired primarily or with a fascia graft 14 of the fascia lata, the temporalis fascia, or with other dura substitutes. Mild dessicating diathermy is advocated to destroy any tags of epithelium in cases whereby a good resection of tissue is not possible. 4 Malignant change can occur in the epithelial lining of intradiploic epidermoid cysts. Yanai et al 38 reported 5 cases with malignant transformation out of a series of about 100 intradiploic epidermoid cysts collected from the literature. It seems that epidermoid cysts that have undergone several operations and repeated inflammations are susceptible to cancer formation. 13 •38 •39 In conclusion, the diagnosis of orbital intradiploic epidermoid cysts is greatly aided by high-resolution CT scans, especially with bone window settings. Complete excision is required to prevent recurrence with the potential for subsequent malignant transformation.
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30. Bullock JD, Bartley GB. Dynamic proptosis. Am J Ophthalmol1986; 102:104-10. 31. Whitney CE, Leone CR Jr, Kincaid MC. Proptosis with mastication: an unusual presentation of an orbital dermoid cyst. Ophthalmic Surg 1986; 17:295-8. 32. Nager GT. Epidermoids involving the temporal bone: clinical radiological and pathological aspects. Laryngoscope 1975; 85(Pt. 2, Suppl 2):1-21. 33. Haessly M, Lagier R. Anatomico-radiological study of intraosseous epidermoid cysts. ROFO 1982; 137:48-54. 34. Peeters FLM. Die Differentialdiagnose benigner, solitarer Defekte im Schadeldach. Fortschr Geb Rontgenstr Nuklearmed 1972; 117:625-
9. 35. Constans JP, Meder JF, De Divitiis E, et al. Giant intradiploic epidermoid cyst of the skull. Report of two cases. J Neurosurg 1985; 62:445-8. 36. Holthusen W, Lassrich MA, Steiner C. Epidermoids and dermoids of the calvarian bones in early childhood: their behavior in the growing skull. Pediatr Radiol1983; 13:189-94. 37. Eijpe AA, Koornneef L, Verbeeten B Jr, et al. Cholesterol granuloma of the frontal bone: CT diagnosis. J Comput Assist Tomogr 1990; 14: 914-7. 38. Yanai Y, Tsuji R, Ohmori S. et al. Malignant change in an intradiploic epidermoid: report of a case and review of the literature. Neurosurgery 1985; 16:252-6. 39. Haig PV. Primary epidermoids of the skull: including a case with malignant change. AJR Am J Roentgenol1956; 76:1076-80.
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