A 10-year-old 7-kg (15.4-lb) neutered male Shih Tzu was referred for evaluation because of a sudden onset of dullness and intermittent vomiting of 1 to 2 weeks’ duration. Two days prior to evaluation, clinical signs had worsened and 1 seizure was reported. On the day of evaluation, the dog was quiet, alert, and responsive. The remaining findings of the physical examination, including postural reactions and cranial and spinal nerve reflexes, were unremarkable except for a 3.5 × 2.5-cm soft, dome-shaped mass in the right occipital region of the head that had been present for an indeterminate period.
Radiography of the head revealed a focal, radiolucent mass involving the bone in the right occipital region with well-defined sclerotic margins, except for an irregular, destructive caudal margin associated with extracranial expansion (Figure 1). Cytologic evaluation of a fine-needle aspirate sample of the mass revealed anucleate squamous epithelial cells, basophilic debris, and low numbers of nucleated squamous epithelial cells and RBCs. Results of a CBC and serum biochemical analyses were within reference limits, and thoracic radiographs were unremarkable.
Lateral radiographic (A) and pre- (B) and postcontrast (C) transverse CT images at the level of the tympanic bullae of a 10-year-old neutered male Shih Tzu with an intradiploic epidermoid cyst. A—The cyst is radiolucent with well-defined sclerotic bony margins (black arrow) except for an irregular, destructive caudal bony margin (white arrow) associated with extracranial expansion. B—The cyst has expanded both intra- and extracranially and has inhomogeneous hypoattenuation (asterisk) relative to the adjacent brain parenchyma. C—In the postcontrast image, the cyst has thin rim enhancement (arrow).
Citation: Journal of the American Veterinary Medical Association 257, 2; 10.2460/javma.257.2.183
Lateral radiographic (A) and pre- (B) and postcontrast (C) transverse CT images at the level of the tympanic bullae of a 10-year-old neutered male Shih Tzu with an intradiploic epidermoid cyst. A—The cyst is radiolucent with well-defined sclerotic bony margins (black arrow) except for an irregular, destructive caudal bony margin (white arrow) associated with extracranial expansion. B—The cyst has expanded both intra- and extracranially and has inhomogeneous hypoattenuation (asterisk) relative to the adjacent brain parenchyma. C—In the postcontrast image, the cyst has thin rim enhancement (arrow).
Citation: Journal of the American Veterinary Medical Association 257, 2; 10.2460/javma.257.2.183
Lateral radiographic (A) and pre- (B) and postcontrast (C) transverse CT images at the level of the tympanic bullae of a 10-year-old neutered male Shih Tzu with an intradiploic epidermoid cyst. A—The cyst is radiolucent with well-defined sclerotic bony margins (black arrow) except for an irregular, destructive caudal bony margin (white arrow) associated with extracranial expansion. B—The cyst has expanded both intra- and extracranially and has inhomogeneous hypoattenuation (asterisk) relative to the adjacent brain parenchyma. C—In the postcontrast image, the cyst has thin rim enhancement (arrow).
Citation: Journal of the American Veterinary Medical Association 257, 2; 10.2460/javma.257.2.183
The dog was subsequently referred for CT and MRI of the head. At the time of this referral, no additional seizures were reported. The dog was premedicated with butorphanol tartratea (0.2 mg/kg [0.09 mg/lb], IV) and midazolam hydrochloridea (0.2 mg/kg, IV), and anesthesia was induced with propofolb (3 mg/kg [1.4 mg/lb], IV). The dog was orotracheally intubated, and anesthesia was maintained with sevofluranec in oxygen. Pre- and postcontrastenhanced CTd and MRId examinations were performed by use of iohexole (700 mg of iodine/kg [318 mg of iodine/lb], IV) and gadodiamidef (0.1 mmol/kg [0.045 mmol/lb], IV), respectively, without complications. For MRI, T2-weighted, T1-weighted, FLAIR, and postcontrast T1-weighted images were sequentially obtained.
Computed tomographic images showed a mass that had expanded intra- and extracranially, inhomogeneous hypoattenuation (mean attenuation of 3 measurements, 17.8 HU) relative to the parenchyma of the brain, and thin rim enhancement with contrast (Figure 1). Images obtained with MRI showed that the internal contents of the mass had a similar signal to that of CSF in T2-weighted images, a heterogeneous high signal relative to the surrounding soft tissue in T1-weighted images, incomplete suppression with FLAIR (ie, high signal), and mild rim enhancement in postcontrast T1-weighted images (Figure 2). Peripheral portions of the mass had strong hyperintensity in T1-weighted images and indistinct rim enhancement in postcontrast T1-weighted images. In both T2- and T1-weighted images, the mass, demarcated by a distinct margin of hypointensity, compressed the cerebellum.
Transverse MRI images of an intradiploic epidermoid cyst in the right caudal aspect of the occipital region of the head of the dog in Figure 1. A—The cyst has similar signal intensity to that of CSF in this T2-weighted image. B—The cyst has incomplete FLAIR suppression. C—The cyst has heterogeneous hyperintensity in this T1-weighted image. D—The rim of the epidermoid cyst is mildly enhanced in this postcontrast T1-weighted image.
Citation: Journal of the American Veterinary Medical Association 257, 2; 10.2460/javma.257.2.183
Transverse MRI images of an intradiploic epidermoid cyst in the right caudal aspect of the occipital region of the head of the dog in Figure 1. A—The cyst has similar signal intensity to that of CSF in this T2-weighted image. B—The cyst has incomplete FLAIR suppression. C—The cyst has heterogeneous hyperintensity in this T1-weighted image. D—The rim of the epidermoid cyst is mildly enhanced in this postcontrast T1-weighted image.
Citation: Journal of the American Veterinary Medical Association 257, 2; 10.2460/javma.257.2.183
Transverse MRI images of an intradiploic epidermoid cyst in the right caudal aspect of the occipital region of the head of the dog in Figure 1. A—The cyst has similar signal intensity to that of CSF in this T2-weighted image. B—The cyst has incomplete FLAIR suppression. C—The cyst has heterogeneous hyperintensity in this T1-weighted image. D—The rim of the epidermoid cyst is mildly enhanced in this postcontrast T1-weighted image.
Citation: Journal of the American Veterinary Medical Association 257, 2; 10.2460/javma.257.2.183
The dog was returned for surgical removal of the mass 12 days later, and during this period, the dog did not have any seizures. Mannitolg (0.5 g/kg [0.23 g/lb], IV) and maropitant citrateh (1 mg/kg [0.45 mg/lb], SC) were administered. Then, the dog was premedicated with butorphanol (0.2 mg/kg, IV), midazolam (0.2 mg/kg, IV), and cefazolin sodiumi (22 mg/kg [10 mg/lb], IV). Anesthesia was induced with alfaxalonej (1.5 mg/kg [0.7 mg/lb], IV). After the dog was orotracheally intubated, anesthesia was maintained with isofluranek in oxygen. After administration of loading doses of 2% lidocaine hydrochlorideg (1 mg/kg, IV) and ketaminei (1 mg/kg, IV), butorphanol (0.2 mg/kg/h), lidocaine (3 mg/kg/h), and ketamine (10 μg/kg/min [4.5 μg/lb/min]) were coadministered as a CRI. Additional butorphanol (0.1 mg/kg, IV) and ketamine (0.5 mg/kg, IV) boluses were administered as required for analgesia. Cefazolin (22 mg/kg, IV) was administered every 120 minutes throughout surgery.
The dog was positioned in sternal recumbency, and the dorsal aspect of the head and neck was clipped of hair and aseptically prepared for surgery. A 13-cm curved, rostral-to-caudal skin incision was made centrally over the mass (Figure 3). After subcutaneous tissues were separated by sharp and blunt dissection, the mass was seen under the caudal aspect of the right temporalis muscle. Portions of the occipitalis and temporalis muscles were tightly adhered to lytic portions of the parietal and occipital bones near the external occipital protuberance. The right temporalis muscle was incised from a lateral to medial direction at the cranial extent of the mass to better expose its capsule. After this incision was made, the capsule of the mass ruptured, thereby exposing a yellow, lipid-like substance. The incised muscle was then retracted cranially, and the contents of the mass were removed with suction and forceps. Next, the capsule was excised. To ensure complete removal of the capsule, portions of the parietal and occipital bones were excised with a pneumatic burr and rongeur. Yet, the capsule of the mass attached to the dura mater was thin and easily separated from the dura mater with wet cotton swabs. The dura mater was intact; therefore, excision of the capsule was not suspected to have damaged the neural tissue. The cavity resulting from excision of the mass was repeatedly lavaged with saline (0.9% NaCl) solution, and the bony margins of the cavity (parietal and occipital bones) were smoothed with a pneumatic burr and rongeur.
Intraoperative images obtained during removal of an intradiploic epidermoid cyst from the head of the dog in Figure 1; the dog is positioned in sternal recumbency. A—A 13-cm curved, rostral-to-caudal skin incision was made centrally over the cyst, which was under the caudal aspect of the right temporalis muscle. B—Rupture of the capsule of the cyst exposed yellow, lipid-like material. C—Removal of the contents of the cyst exposed a cavity and remaining capsule. D—The bony defect created after complete removal of the cyst was covered with titanium mesh. The dog's right is to the right and the rostral aspect is to the top of the images.
Citation: Journal of the American Veterinary Medical Association 257, 2; 10.2460/javma.257.2.183
Intraoperative images obtained during removal of an intradiploic epidermoid cyst from the head of the dog in Figure 1; the dog is positioned in sternal recumbency. A—A 13-cm curved, rostral-to-caudal skin incision was made centrally over the cyst, which was under the caudal aspect of the right temporalis muscle. B—Rupture of the capsule of the cyst exposed yellow, lipid-like material. C—Removal of the contents of the cyst exposed a cavity and remaining capsule. D—The bony defect created after complete removal of the cyst was covered with titanium mesh. The dog's right is to the right and the rostral aspect is to the top of the images.
Citation: Journal of the American Veterinary Medical Association 257, 2; 10.2460/javma.257.2.183
Intraoperative images obtained during removal of an intradiploic epidermoid cyst from the head of the dog in Figure 1; the dog is positioned in sternal recumbency. A—A 13-cm curved, rostral-to-caudal skin incision was made centrally over the cyst, which was under the caudal aspect of the right temporalis muscle. B—Rupture of the capsule of the cyst exposed yellow, lipid-like material. C—Removal of the contents of the cyst exposed a cavity and remaining capsule. D—The bony defect created after complete removal of the cyst was covered with titanium mesh. The dog's right is to the right and the rostral aspect is to the top of the images.
Citation: Journal of the American Veterinary Medical Association 257, 2; 10.2460/javma.257.2.183
The skull defect consisted of most of the occipital bone and the caudal part of the right parietal bone. The defect was reconstructed with titanium mesh,l which was trimmed and contoured with mesh cutters and then formedm to fit the defect (Figure 3). The mesh was secured to the skull with 12 self-drilling, self-tapping, 1.4-mm-diameter × 3-mm-long titanium screws.n The temporal muscles were apposed with 3-0 polydioxanoneo in a horizontal mattress pattern. The deep subcutaneous tissue was closed with 4-0 polydioxanoneo in a simple continuous pattern. Final closure of the skin incision consisted of a continuous intradermal pattern with 4-0 polydioxanone and a simple interrupted pattern with 3-0 nylon.p The mass was submitted for histologic examination.
After surgery, the dog was extubated but did not regain full consciousness and began to paddle all of its limbs. Midazolam (0.3 mg/kg [0.14 mg/lb], IV) was administered and paddling ceased. A combination of butorphanol (0.2 mg/kg/h), lidocaine (3 mg/kg/h), and ketamine (5 μg/kg/min [2.3 μg/lb/min]) was maintained as a CRI. The dog became fully conscious 12 hours after surgery. Over 24 hours, the rate of the CRI was progressively decreased, and at its discontinuation, analgesia was provided through administration of meloxicam (0.2 mg/kg, SC, q 24 h) and butorphanol (0.3 mg/kg, IV, q 6 h).
Postoperative care included the administration of cefazolin (22 mg/kg, IV, q 12 h) and famotidine (0.5 mg/kg [0.23 mg/lb], IV, q 12 h). Three days after surgery, the dog was ambulatory but had mild ataxia, hypermetria, and head tremors. Seven days after surgery, the dog was discharged from the hospital despite still having hypermetria and head tremors. Medications prescribed at discharge were cefadroxilq (22 mg/kg, PO, q 12 h), firocoxibr (5 mg/kg [2.3 mg/lb], PO, q 24 h), and tramadols (3 mg/kg, PO, q 8 h).
Several specimens of the mass were fixed in neutral-buffered 10% formalin, processed routinely, and stained with H&E stain for histologic examination. Results of examination revealed a cyst lined by well-differentiated, stratified squamous epithelium with keratinization and filled with a large amount of lamellar keratin (Figure 4). The stratified squamous epithelial cells and lamellar keratin were immunoreactive for cytokeratin AE1/AE3, which indicated the cyst to be of epithelial cell origin. The histologic diagnosis was an epidermoid cyst, most likely an intradiploic epidermoid cyst because of its anatomic location and the presence of a bony defect.
Photomicrographs of sections of an intradiploic epidermoid cyst excised from the right caudal aspect of the occipital region of the head of the dog in Figure 1. A—The cyst was lined by well-differentiated, stratified squamous epithelium with keratinization. H&E stain; bar = 2 mm. B—The cyst contained a large amount of lamellar keratin (arrow). H&E stain; bar = 200 μm. C—The stratified squamous epithelial cells that line the cyst were immunoreactive (arrow) for cytokeratin AE1/AE3. Immunohistochemical stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 257, 2; 10.2460/javma.257.2.183
Photomicrographs of sections of an intradiploic epidermoid cyst excised from the right caudal aspect of the occipital region of the head of the dog in Figure 1. A—The cyst was lined by well-differentiated, stratified squamous epithelium with keratinization. H&E stain; bar = 2 mm. B—The cyst contained a large amount of lamellar keratin (arrow). H&E stain; bar = 200 μm. C—The stratified squamous epithelial cells that line the cyst were immunoreactive (arrow) for cytokeratin AE1/AE3. Immunohistochemical stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 257, 2; 10.2460/javma.257.2.183
Photomicrographs of sections of an intradiploic epidermoid cyst excised from the right caudal aspect of the occipital region of the head of the dog in Figure 1. A—The cyst was lined by well-differentiated, stratified squamous epithelium with keratinization. H&E stain; bar = 2 mm. B—The cyst contained a large amount of lamellar keratin (arrow). H&E stain; bar = 200 μm. C—The stratified squamous epithelial cells that line the cyst were immunoreactive (arrow) for cytokeratin AE1/AE3. Immunohistochemical stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 257, 2; 10.2460/javma.257.2.183
At reexamination 2 weeks after surgery, hypermetria and head tremors had lessened. Hypermetria and head tremors had resolved by 3 weeks after surgery, and the dog remained physically normal at 8 weeks after surgery. No recurrence of clinical signs was evident on reexamination 25 months after surgery.
Discussion
Intracranial epidermoid cysts are uncommon in animals and people.1–5 In human medicine, such epidermoid cysts represent approximately 1% of all intracranial masses.5 Intracranial epidermoid cysts are believed to be congenital and formed by retention of epithelial elements within the neural groove during closure of the neuronal tube in embryonic development.2,6 Lined by squamous epithelium and containing keratinocytes, keratinaceous debris, and cholesterol, epidermoid cysts may develop within the diploë, the cancellous bone separating the inner and outer layers of the cortical bones of the skull.1,3 In people, about 25% of CNS epidermoid cysts are intradiploic.7 Specifically, intradiploic epidermoid cysts are thought to be derived from ectodermal remnants that remain within the skull bones during embryonic development.3,8 Although intracranial epidermoid cysts have been detected in dogs at necropsy or at surgery, intradiploic epidermoid cysts have not been reported in dogs.1,2,9–13
Intradiploic epidermoid cysts are benign, slow-growing, small to moderately sized masses that can be associated with any part of the skull.3,8 In people, an intradiploic epidermal cyst commonly manifests as a painless lump of the scalp and may grow to an enormous size without inducing symptoms.7 Symptoms, commonly tenderness and headache, generally occur in adulthood.3,7 In rare cases, large intradiploic epidermoid cysts can induce intracranial hypertension,3,14 seizures,7 or focal neurologic signs.3 The dog of the present report had a sudden onset of dull mentation, vomiting, and seizure activity at 10 years of age.
Radiographically, an intradiploic epidermoid cyst may appear as a large osteolytic area with sclerotic bony margins and extracranial expansion.13 The most common CT finding is hypoattenuation or isoattenuation relative to the adjacent cerebral cortex of an extradural, intracranial mass without contrast enhancement.7 Its signal intensity will vary for T1-weighted MRI images yet will consistently be hyperintense for T2-weighted MRI images.13 High signal on T1-weighted images of intracranial and intradiploic epidermoid cysts may be caused by hemorrhage or a mix of triglycerides and residues of unsaturated fatty acid.7,15 Typically, FLAIR suppression of an epidermoid cyst is incomplete because of the cyst's protein and keratin content.9,16 Imaging findings for the dog of the present report were consistent with those typical of intradiploic epidermoid cysts.
Surgical removal of a large intradiploic epidermoid cyst involves complete removal of the capsule, which necessitates careful dissection of the capsule from bone and dura mater.13,17 In people, complete removal of the capsule decreases the chance of recurrence and increases the chance of a favorable long-term prognosis.3,7,13,18 Incomplete removal of an intracranial epidermoid cyst has been reported in a dog.8 The capsule of the epidermoid cyst of that dog was adhered to the surrounding neurovascular tissue, making complete removal of the capsule impossible without damaging the neurovascular tissue.8 For the dog of the present report, we completely removed the intradiploic epidermoid cyst and its capsule. Although the intradiploic epidermoid cyst had compressed the cerebellum and its capsule was adhered to the adjacent bone, muscle, and dura mater, the dura mater was intact and we easily separated the capsule from the dura mater with wet cotton swabs. Complete removal of the intradiploic epidermoid cyst from the dog of the present report was the likely reason for the excellent outcome, compared with that of the dog of the previous report.8
Cranioplasty may be necessary to replace a large bone defect after craniectomy.3 Titanium mesh has been previously used for cranioplasty in a dog,19 and the bony defect of the dog of the present report was covered with titanium mesh. Titanium mesh has the advantages of radiolucency, low density, and corrosion resistance, and it may be less likely to act as a nidus for bacterial infection.19,20
In people, intradiploic epidermoid cysts may rarely undergo transformation into squamous cell carcinoma.21 Incomplete removal of the cyst, repeated surgeries to excise the cyst, and chronic osteomyelitis may precipitate malignant transformation.7,17,21,22 The intradiploic epidermoid cyst in the dog of the present report was histologically benign despite its size. Nevertheless, we believed its surgical removal was necessary to avoid neurologic complications associated with its progressive enlargement.13 Fortunately, the capsule of the intradiploic epidermoid cyst was easily separated from the dura mater; therefore, the cyst and its capsule could be completely removed.
For the dog of the present report, head tremors and hypermetria occurred after recovery from general anesthesia and persisted for 3 weeks. Head tremors and hypermetria are common signs of cerebellar disease.23 Neurologic signs may develop because of compression of the neural tissue by the epidermoid cyst.1,2 The intradiploic epidermoid cyst in the dog of the present report had severely compressed the cerebellum. Although the dog did not have head tremors and hypermetria at presentation, inflammation caused by surgical manipulation of the dura mater and cerebellar edema caused by rapid expansion of the cerebellum likely precipitated the head tremors and hypermetria. The head tremors and hypermetria likely slowly resolved as inflammation and edema resolved.
Physicians have been wary of administering ketamine to their patients with intracranial disease because of its potential to increase intracranial pressure.24 Although the authors of some studies24,25 suggested ketamine may exacerbate intracranial disease as a result of increased cerebral elastance (ie, decreased intracranial compliance to changes in volume), the authors of other studies26,27 suggested ketamine has little effect on intracranial pressure in people. In the report8 of a dog with an intracranial epidermoid cyst, postoperative analgesia consisted of a combination of morphine, lidocaine, and ketamine. The neurologic condition of that dog deteriorated; therefore, ketamine administration may have contributed to its deterioration. However, the intracranial epidermoid cyst of that dog was not completely excised, and because of its location, the cyst had been causing dilation of the ventricular system. These factors likely contributed to the deterioration of that dog. In the dog of the present report, analgesia was achieved with a CRI of a combination of ketamine, butorphanol, and lidocaine without complication.28
To the authors’ knowledge, this was the first report describing an intradiploic epidermoid cyst in a dog. Although intradiploic epidermoid cysts are rare, neurologic signs, a hard lump arising from the bones of the skull, and diagnostic imaging should aid with the diagnosis for dogs. The absence of clinical signs at 25 months after removal of the cyst for the dog of present report suggested that the prognosis can be good with complete removal.
Acknowledgments
No third-party funding or support was received in connection with this study. The authors declare that there were no conflicts of interest.
ABBREVIATIONS
| CRI | Constant rate infusion |
Footnotes
Myungmoon Pharm Co Ltd, Hwaseong, Republic of Korea.
Provive 1%, Myungmoon Pharm Co Ltd, Seoul, Republic of Korea.
Piramal Critical Care Inc, Bethlehem, Pa.
Siemens Medical, Munich, Germany.
Omnipaque, GE Healthcare, Cork, Ireland.
Omniscan, GE Healthcare, Cork, Ireland.
Dai Han Pharm Co Ltd, Seoul, Republic of Korea.
Cerenia, Zoetis Korea Ltd, Seoul, Republic of Korea.
Yuhan Co Ltd, Seoul, Republic of Korea.
Alfaxan, Jurox, Rutherford, Australia.
Ifrane, Hana Pharm Co Ltd, Gyeonggi, Republic of Korea.
3D Dynamic Mesh, Jeil Medical Co, Seoul, Republic of Korea.
3D Mesh R-former, Jeil Medical Co, Seoul, Republic of Korea.
Jeil Medical Co, Seoul, Republic of Korea.
PDS, Ethicon Inc, Somerville, NJ.
Dafilon, B. Braun Surgical SA, Rubí, Spain.
Il-Yang Pharmaceutical Co Ltd, Seoul, Republic of Korea.
Previcox, Merial, Lyon, France.
Toranzin, Samsung Pharmaceutical Co Ltd, Seoul, Republic of Korea.
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