Keywords
dermoid cyst - epidermal cyst - head and neck neoplasms - skull base - nasal cavity
- pterygopalatine fossa
Introduction
Dermoid cysts are congenital defects involving pluripotent stem cells arising from
an ectopic site. This disease presents a slightly higher predominance in males, and
most patients are diagnosed within the first fourth decades of life.[1] Although up to one third of dermoid cysts are found at birth, most of them are diagnosed
in the second and third decades.[2]
Almost 7% of all dermoids are located in the head and neck.[3] They are frequently found in the region of the lateral part of the eyebrow, in the
periorbital region, and in the midline nasal region. In the neck they usually occur
in the submental region, above the hyoid and always in the midline.[3] This tumor accounts for fewer than 5% of all intracranial masses.[2]
Tumors arising from the sinonasal region usually present late as their symptoms are
often banal and may be overlooked by patients and their clinicians. The recent onset
of unilateral nasal symptoms, without improvement with medical therapy, and orbital
and neurologic symptoms should be investigated with imaging studies. Computed tomography
(CT) and magnetic resonance imaging (MRI) are used to characterize tumors of this
region.[4]
Endoscopic sinus surgery is a well-established technique for the treatment of sinus
diseases, including chronic sinusitis and nasal neoplasms. Endoscopic sinus surgery
to approach nasal neoplasms is limited, as the tumor can be too extensive.[5] In this report, we discuss diagnosis, differential diagnosis, and possible approaches
to lesions arising from the pterygopalatine fossa.
Case Report
A 23-year-old man was admitted to a tertiary care center after a car accident, in
which he sustained a pelvic/femoral fracture. There was no evidence of any associated
injury, and a conversion to tracheostomy after long-term intubation was performed.
He also presented a first episode of generalized tonic-clonic seizure. In addition,
he presented reduced visual acuity in the left side.
The patient was referred for brain MRI; a heterogeneous ovoid lesion hyperintense
in T2-weighted imaging in the pterygopalatine fossa was discovered. As a matter of
fact, this lesion was indenting the middle fossa and was closely related to the maxillary
artery, sphenopalatine ganglia, and maxillary posterior wall. The patient was referred
to the Otolaryngology Department of Clinics Hospital–University of São Paulo.
Prior to surgery, a wide range of differential cell counts were obtained. Laboratory
workup, including a complete blood count with differentials and determination of liver
enzymes and electrolytes, showed no abnormal findings. Brain CT showed a heterogeneous
lobulated lesion in the left masticator space (infratemporal region), 3 × 3, 5 × 2
cm wide, medial to lateral pterygoid muscle, with erosion of the inferior wall of
foramen rotundum ([Fig. 1]). We repeated brain MRI, which showed a lobulated extra-axial formation in the left
masticator space, between lateral and medial pterygoid muscles, with fat heterogeneous
tissue, hypointense in T2-weighted image, gadolinium-enhanced in T1-weighted image
([Fig. 2]). There were small hyperintense lesions in T1-weighted images in the suprasellar
cistern and in the sylvian fissure, suggesting previous dermoid rupture ([Fig. 2B]).
Fig. 1 Computed tomography showing a heterogeneous lobulated lesion in the infratemporal
region.
Fig. 2 Magnetic resonance imaging (MRI) of the lesion with heterogenous content in the inferior
region. (A, B) T1-weighted coronal MRI. (C) T1-weighted axial MRI showing invasion
of the infratemporal fossa.
A transpterygoid transnasal endoscopic approach and resection of the lesion was performed.
The puncture of the lesion showed initially a transparent thick liquid. Unexpectedly,
hair and sebaceous glands were found inside the cyst capsule ([Fig. 3]). The cyst was excised completely.
Fig. 3 Intraoperative endoscopic visualization of the dermoid cyst.
Histopathologic examination confirmed the diagnosis of a dermoid cyst. The patient's
postoperative course was unremarkable.
Discussion
Benign and malignant tumors can arise from any of the structures within the infratemporal
fossa and parapharyngeal space.[6] Dermoid inclusion cysts are benign tumors and are mainly unilocular and expand slowly,
enlarging over years or decades, by the accumulation of cutaneous products. They may
show lipid content, derived from sebaceous secretions, and secretions of apocrine
sweat glands and hair.[2]
The causes of dermoids include failure of surface ectoderm to separate from underlying
structures and sequestration of surface ectoderm at lines of epithelial fusion during
embryonic development. Most congenital dermoid cysts probably arise due to an embryologic
accident during early stages of development, between the third and fifth weeks of
gestation.[2]
[3]
Clinical examination of the fossa pterygoid is difficult because it is deep lying
and not easily accessible. Lesions are often discovered only at a late stage either
because there are no clinical signs or, if they do occur, they are so common as to
be overlooked.[1]
[6]
[7] In our case, the diagnosis was incidental. Tumors that arise in pterygopalatine
fossa are usually asymptomatic. CT and MRI provide precise imaging information and
may be necessary for making the diagnosis. In addition, imaging data can help to differentiate
infection from tumor lesions and primary tumors from secondary tumors.[1]
[7] Although they are slow-growing, dermoid inclusions cysts produce pressure changes
on surrounding structures that are visible at radiograph study.
In a case series, Yu et al evaluated 86 patients with tumoral lesions of pterygopalatine
and infratemporal spaces.[1] Most of the lesions (81%) originated in oral and maxillofacial regions other than
pterygopalatine and infratemporal spaces and extended to this region. Only one case
of teratoma was found. The most frequent diseases reported among the other cases were
squamous cells carcinoma, adenoid cystic carcinoma, inflammatory disease, and hemangioma.
Differential diagnosis in cases of tumoral lesions in pterygoid fossa should be performed
([Table 1]).[1]
[8]
[9]
[10]
[11]
[12]
[13]
Table 1
Differential diagnosis of lesions in pterygoid region
|
Meningoencephalocele
|
Malignant lymphoma
|
|
Maxillary sinus carcinoma
|
Squamous cell carcinoma
|
|
Olfactory neuroblastoma
|
Inflammatory disease
|
|
Osteochondroma
|
Adenoid cystic carcinoma
|
|
Cholesterol granuloma
|
Adenocarcinoma
|
|
Myoepithelial carcinoma
|
Hemangioma
|
|
Ameloblastoma
|
Leiomyosarcoma
|
|
Malignant fibrohistiocytoma
|
Undifferentiated carcinoma
|
|
Giant-cell tumor
|
Chondrosarcoma
|
|
Keratocyst
|
Osteoblastoma
|
|
Mixed tumor
|
Malignant myoepithelioma
|
|
Mucoepidermoid carcinoma
|
Liposarcoma
|
|
Hemangiopericytoma
|
Hemangioendothelioma
|
|
Undifferentiated sarcoma
|
Malignant mixed tumor
|
|
Lymphangioma
|
Neurofibroma
|
|
Rhabdomyosarcoma
|
|
Treatment of dermoid cysts consists of complete surgical excision of the lesion, avoiding
recurrence.[6] Rupture of dermoid cysts can produce severe chemical meningitis, usually attributed
to the irritating effects of the cholesterol in the cellular debris.[2] In our case, brain MRI showed signs of previous rupture, which may account for the
patient's epilepsy.
Uppal et al excised a dermoid cyst in the infratemporal fossa, extending inferiorly
to the parapharyngeal space, using a lateral approach to that region.[6] In our case, we performed a minimally invasive treatment, using an endoscopic transnasal
transpterygoid approach with a wide access to the lesion. It was possible to proceed
with complete excision of the tumor, without intraoperative complications.
The clinical diagnosis and management of these lesions can be challenging because
of the relative inaccessibility of the region, which contains the maxillary artery,
the maxillary nerve, and the pterygopalatine ganglia, with its branches.
Surgical advantages of the endoscopic endonasal approach in comparison with traditional
transcranial approaches include a more direct midline exposure, decreased brain parenchyma
injury, and lack of neurovascular structure manipulation. From the patient's perspective,
decreased surgery time, decreased length of stay, increased patient comfort, and lack
of external incision are advantages of the endoscopic endonasal approach.
Although rare, dermoid cysts should be considered in the differential diagnosis of
expansive lesions in the pterygopalatine fossa and can be excised by a transnasal
transpterygoid endoscopic approach.
