|
 |
|
CASE REPORT |
|
|
|
| Ahead of print
publication |
| |
Pediatric posterior fossa dermoid cyst: Diagnostic dilemma
Batuk D Diyora, Subhashish Dey, Ashish Dubey, Kavin Devani, Mehool Patel, Gagan Dhal
Department of Neurosurgery, LTMMC & LTMG Hospital, Sion, Mumbai, Maharashtra, India
| Date of Submission | 04-Jan-2021 |
| Date of Decision | 29-May-2021 |
| Date of Acceptance | 27-Mar-2021 |
| Date of Web Publication | 07-Jan-2022 |
Correspondence Address:
Batuk D Diyora,
Department of Neurosurgery, LTMMC & LTMG Hospital, Sion, Mumbai 400022, Maharashtra.
India
 Source of Support: None, Conflict of Interest: None DOI: 10.4103/jpn.JPN_4_21
 Abstract | | |
Dermoid cysts are rare congenital lesions of the brain. They are commonly located in the supratentorial region. Infratentorial dermoid cysts are uncommon. They can occupy cerebellopontine angle, midline posterior fossa, or brain stem. Midline post fossa dermoid cysts can be confused with another common lesion in this location. We describe a case of midline posterior fossa dermoid cyst in a 6-year-female child who presented with signs and symptoms of raised intracranial pressure. Magnetic resonance imaging showed posterior fossa lesion which was hypointense on T1-weighted images, hyperintense on T2-weighted images, and not enhancing on intravenous contrast administration. The lesion showed restricted diffusion on diffusion-weighted images. Radiological diagnosis was an epidermoid cyst. However, during surgery, we found hair follicles. Histopathological examination revealed dermoid cyst. The child recovered completely following cyst excision. We present a case of a posterior fossa dermoid cyst mimicking epidermoid cyst.
Keywords: Dermoid cyst, epidermoid cyst, posterior fossa
| Introduction | |  |
Dermoid cysts are rare congenital lesions of brain and comprise about 0.1–0.7% of intracranial tumors.[1] They are commonly located in the supratentorial region. Infratentorial dermoid cysts are rare.[2],[3],[4],[5],[6],[7],[8],[9],[10] Because of their rarity, they can be easily misdiagnosed. These lesions should be differentiated from other common posterior fossa midline lesions such as pilocytic astrocytoma, arachnoid cyst, epidermoid cyst, or trapped fourth ventricle. They contain thick, foul-smelling, yellowish material from the secretion of sebaceous glands, lipid metabolites, and whorls of hair, calcifications, and desquamated epithelium. They are often associated with dermal sinus tract which may be either complete or incomplete.[11] We present a case of posterior fossa dermoid cyst which was mimicking epidermoid cyst in a child and a review literature.
| Case Report | | |
A 6-year-female child presented with holocranial headache and intermittent vomiting for 3 months. Neurological examination revealed no abnormality except grade I papilloedema in both eyes. Her computed tomography (CT) scan revealed a hypodense extra-axial mass lesion of about 3.5 cm × 3 cm size in midline posterior fossa, which was not enhancing on intravenous contrast administration [Figure 1]. She underwent magnetic resonance imaging (MRI) study of the brain which revealed almost similar size contrast non-enhancing mass lesion [Figure 2]C in the midline posterior fossa which appeared homogeneous hypointense on T1-weighted images [Figure 2]A and homogeneous hyperintense on T2-weighted images [Figure 2]B. The lesion showed restricted diffusion on diffusion-weighted (DW) images [Figure 2]D. Partial enlargement of fourth and third ventricles as well as lateral ventricles was noted. Mass effect in the form of displacement of vermis and bilateral cerebellar tonsil was also noted. Radiological diagnosis was posterior fossa epidermoid cyst. Microsurgical excision of the posterior fossa mass cystic lesion was performed under general anesthesia. In prone position via midline vertical suboccipital incision, suboccipital craniectomy was performed and dura opened in a “Y”-shaped manner. On gentle retraction of cerebellar tonsils, well-capsulated lesion was found which was entered [Figure 3]A. Grayish yellow, semisolid tumor tissue was found which was excised in piecemeals. A large bunch of hairs found was mixed with the tumor tissue which was also excised [Figure 3]B. Complete excision of the lesion along with its capsule ensured. Histopathological examination of the tumor tissue revealed stratified squamous epithelium with keratinous material with few hair follicles. These features were suggestive of a sebaceous glands dermoid cyst [Figure 3]C. Initial postoperative course was uneventful; however, the child developed headache and vomiting on seventh post-operative day so that MRI brain was performed which revealed hydrocephalus. MRI also revealed no evidence of residual disease [Figure 4]A and B. The child underwent right-sided ventriculoperitoneal shunt. His clinical symptoms disappeared following shunt. At six-month follow-up, the child was completely asymptomatic. | Figure 1: CT scan brain showing an extra-axial hypodense mass lesion in the posterior fossa with compression of the fourth ventricle and dilated temporal horns on both sides
Click here to view |
 | Figure 2: MRI of the brain showing contrast non-enhancing lesion (C) in the posterior fossa which is hypointense on T1-weighted images (A) and hyperintense on T2-weighted images (C). DW image showing restricted diffusion (D)
Click here to view |
 | Figure 3: Intraoperative photomicrograph showing grayish white tumor capsule (A) and presence of hair (B). Photomicrograph showing cystic lesion with a lining by stratified squamous epithelium containing flakes of keratin and proteinaceous material with evidence of hair follicles (C) (H&E staining)
Click here to view |
 | Figure 4: Post-operative contrast MRI (A) and DW image (B) showing no evidence of the residual lesion
Click here to view |
| Discussion | | |
Misplacement of ectodermal elements into the developing neural tube around 3rd or 5th week of intrauterine life results in the development of dermoid cyst.[12] Dermoid cysts can occupy anywhere in the craniospinal axis. They have a tendency to lie in the midline due to developmental reason. They are more common in brain compared with spinal cord. Posterior fossa at or near the midline is common location.[13] This is due to development of tentorium and falx cerebelli as an imagination of two folds of dura, strictly in the midline of the posterior fossa, which draw in fragments of the skin layer with it.[12] Very rarely, cyst may be located away from the midline into the cerebellum, cerebellopontine angle, or near brainstem.[14] Literature search revealed only 10 reported cases of posterior fossa dermoid cyst [Table 1]. | Table 1: Literature study revealed 10 reported cases of posterior fossa dermoid cyst
Click here to view |
As these cysts are developmental in origin, they are often associated with congenital abnormality; dermal sinus is one of them. Logue and Till classified posterior fossa dermoid cyst into four types based on its relation to the dura and degree of development of dermal sinus: (1) extradural dermoid cyst with a complete sinus; (2) intradural dermoid cyst without a sinus; (3) an intradural dermoid cyst with an incomplete dermal sinus; and (4) an intradural dermoid cyst with a complete dermal sinus. Compared with type 2, all other types are more prone for infective complications.[11] Our case was intradural dermoid cyst without dermal sinus.
Presentation of posterior fossa dermoid cysts is variable. Patients often present with signs and symptoms of raised intracranial pressure which includes headache, vomiting, bradycardia hypertension, and papilledema. Compression of local neurovascular structure due to cyst results in ataxia and cranial nerve palsies. Occasionally, they do present with rupture and resulting hydrocephalus.[15]
Dermoid cysts appear extremely hypodense on CT scan with very low Hounsfield unit (−20 to −140) due to their lipid content. Though peripheral calcification was often seen, perilesional edema is rare. They do not enhance on contrast administration. Hydrocephalus is uncommon with posterior fossa dermoid cysts.[16],[17] On MRI, they appear hyperintense on T1-weighted images and hypo-to-hyperintense on T2-weighted images. They do not enhance on contrast administration. However, atypical imaging findings have being reported.[17] Dermoid cysts need to be differentiated from other cystic lesions of brain such as arachnoid cyst, ependymal cyst, or epidermoid cyst and occasionally cystic glioma. Though DW images play a crucial role in differentiating them from arachnoid cysts and fluid collection, differentiation from epidermoid cysts is extremely difficult.[18]
On measuring random Brownian motion More Details of water molecules within a voxel, epidermoid cyst gives restriction in diffusion due to the presence of protein macromolecules. Dermoid cyst contains lipid and cholesterol elements floating on the proteinaceous material. If this hydrated proteinaceous material is high, then it may also show restriction in Brownian motion and on diffusion MRI. This finding suggests that chemical composition of the cyst content can override imaging features.[19]
In case of symptomatic dermoid cysts, microsurgical excision is the treatment of choice.[1],[12] Compared with other types, type 2 lesions are easier to manage as they are not associated with dermal sinus tract. When the posterior fossa dermoid cyst is associated with dermal sinus, it may get infected. Microsurgical excision of the cyst followed by intravenous antibiotics can bring successful outcomes.[10] Also recurrent meningitis or abscess can result when dermoid cysts are associated with complete dermal sinus, so that prophylactic excision is recommended in cases with asymptomatic dermoid cysts.[11],[12] Very rarely, posterior fossa dermoid cysts can dedifferentiate into squamous cell carcinoma.[20]
| Conclusion | | |
Posterior fossa dermoid cysts are inclusion tumors of the brain and successfully treated with microsurgery with good clinical outcomes. Like epidermoid cyst, occasionally these lesions can show restricted diffusion on DW images and create diagnostic confusion. Though uncommon, these lesions should be considered in the differential diagnosis of posterior fossa mass lesions, especially in pediatric populations.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
| References | | |
| 1. | Yaşargil MG, Abernathey CD, Sarioglu AC Microneurosurgical treatment of intracranial dermoid and epidermoid tumors. Neurosurgery 1989;24:561-7.  |
| 2. | Bizzozero L, Talamonti G, D’Angelo VA, Casadei GP, Arrigoni GL, Collice M Dermoid cyst mimicking hematoma in the posterior fossa. Clin Neurol Neurosurg 1992;94:61-3. |
| 3. | Goh GJ, Page RD, Nixon TE An unusual CT and MR appearance of a posterior fossa dermoid. Eur J Radiol 1995;20:46-7. |
| 4. | Brown JY, Morokoff AP, Mitchell PJ, Gonzales MF Unusual imaging appearance of an intracranial dermoid cyst. AJNR Am J Neuroradiol 2001;22:1970-2. |
| 5. | Neugroschl P, David N, Sadeghi A, Soebert B, Pirotte S, Rorive D Unusual CT features of dermoid cyst in the posterior fossa. Eur Radiol 2002;12:2726-9. |
| 6. | Sanchez-Mejia RO, Limbo M, Tihan T, Galvez MG, Woodward MV, Gupta N Intracranial dermoid cyst mimicking hemorrhage. Case report and review of the literature. J Neurosurg 2006;105:311-4. |
| 7. | Wallace D, Tress B, Kwan PF Radiologically atypical congenital posterior fossa dermoid cyst presenting late in life. J Clin Neurosci 2008;15:835-8. |
| 8. | Morina A, Kelmendi F, Morina Q, Morina D Cerebellar dermoid cyst with contrast enhancement mural nodule: Case report. Acta Clin Croat 2014;53:479-82. |
| 9. | Badri M, Gader G, Bahri K, Zammel I Atypical imaging features of posterior fossa’s dermoid cyst: Case report and review of literature. Surg Neurol Int 2018;9:97. |
| 10. | Segbedji FKK, Tokpo AJ, Nubukpo-Gumenu AA, Quenum LMA, Chakour K, Chaoui MF, et al. Infected intradural dermoid cyst with complete dermal sinus of posterior fossa. World Neurosurg2018;116:219-24. |
| 11. | Logue V, Till K Posterior fossa dermoid cysts with special reference to intracranial infection. J Neurol Neurosurg Psychiatry 1952;15:1-12. |
| 12. | Martínez-Lage JF, Ramos J, Puche A, Poza M Extradural dermoid tumors of the posterior fossa. Arch Dis Childhood 1997;77:427-30. |
| 13. | Brock S, Klenke DA A case of dermoid overlying the cerebellar vermis.Bull Neurol Inst 1931;1:328. |
| 14. | Pai VV, Lowe LH, Castillo M, Huang BY, Shao L Posterior fossa dermoid cysts in association with Klippel–Feil syndrome: Report of three cases. AJNR Am J Neuroradiol 2008;28:1926-8. |
| 15. | Wani AA, Raswan US, Malik NK, Ramzan AU Posterior fossa ruptured dermoid cyst presenting with hydrocephalus. Neurosciences (Riyadh) 2016;21:358-60. |
| 16. | McLendon RE Epidermoid and dermoid tumors. In: Wilkins RH, Rengachary SS, editors. Neurosurgery. 2nd ed. New York: McGraw-Hill; 1996. pp. 959-63. |
| 17. | Osborn AG Diagnostic Neuroradiology. St Louis: Mosby; 1994. pp. 635-6. |
| 18. | Nguyen JB, Ahktar N, Delgado PN, Lowe LH Magnetic resonance imaging and proton magnetic resonance spectroscopy of intracranial epidermoid tumors. Crit Rev Comput Tomogr 2004;45:389-427. |
| 19. | Matthys MK, Long SS, Huisman TA, Pindrik J, Tekes A Posterior fossa dermoid cyst with a sinus tract and restricted diffusion on MR imaging: Value of structural imaging findings and signal characteristics. J Neuroradiol 2012;39:134-5. |
| 20. | Oertel J, Piek J, Müller JU, Vogelgesang S, Warzok R, Gaab RM Posterior fossa squamous cell carcinoma due to dedifferentiation of a dermoid cyst in Klippel-Feil syndrome case illustration. J Neurosurg 2002;97:1244. |
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1]
|
