Introduction :

Epidermoid or epidermal inclusion cysts are formed by the proliferation of epidermal cells within a defined dermal space. Epidermoid cysts can occur at any age, but are more frequent in adulthood. These differ from dermoid cysts in the lack of dermal appendages. The face, neck, periauricular area, and upper trunk are more commonly involved.

Here we report on one such cyst in an adult male

Clinical Profile:

A 40 year old man came with complaints of a swelling in the right submandibular region, gradually increasing in size since three years. He had no history of trauma, pain, local warmth or any discharge. The swelling was soft and mobile without local rise of temperature.

Radiological findings:

1. On frontal and lateral radiographs of the neck, there was a soft tissue swelling in the anterior aspect of the neck in the midline with extension to the right. There were no internal foci of calcification or lucencies and no erosion or periosteal reaction in the mandible. There was no compression of the airway.

2. On Ultrasound examination in B mode and colour Doppler, with a linear transducer at 9 MHz frequency, there was a well-defined, hypoechoic, cystic lesion superficial to the strap muscles with increased through transmission. There were numerous round, ball-like hyperechoic lesions and few linear hyperechoic strands occupying the cystic lesion. The lesion showed no vascularity. Based on ultrasound findings and typical appearance, a provisional diagnosis of dermoid cyst of the neck was made.

3. An MRI with contrast showed a well-defined, superficial, T1/T2 hyperintense cystic lesion in the right sub-mandibular region superficial to the supra-hyoid strap muscles. It contained numerous T1/T2 hyperintense round lesions. There was no suppression of the T1 hyperintense lesions within the cyst on fat-saturation and no contrast enhancement of the lesions or the cyst. DWI and ADC map showed diffusion restriction of the lesions within the cyst with corresponding drop-out on ADC map suggesting true diffusion restriction. 

FIG 1A & 1B

Frontal (A) and lateral (B) clinical images showed a round, swelling in the right sub-mandibular region with no pus point or overlying skin changes.

FIG 2A & 2B 

Frontal (A) and lateral (B) radiographs of the neck showed a soft tissue swelling in the anterior aspect of the neck in the midline with extension to the right. There were no internal foci of calcification or lucencies and no erosion or periosteal reaction in the mandible. There was no compression of the airway.

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FIG 3A & 3B 

B mode (A) and Color Doppler (B) axial images of ultrasound with a linear transducer at 9 MHz frequency showed a well-defined, hypoechoic, cystic lesion superficial to the strap muscles with increased through transmission. There were numerous round, ball-like hyperechoic lesions and few linear hyperechoic strands occupying the cystic lesion. The lesion showed no internal vascularity. 

FIG 4

B mode sagittal image of ultrasound with a linear transducer at 9 MHz frequency showed the lesion cranial to the thyroid gland and superficial to the strap muscles of the neck.

FIG 5A & 5B

T1WI (A) and T2WI (B) of axial sections of MRI neck without contrast showed a well-defined, superficial, T1/T2 hyperintense cystic lesion in the right sub-mandibular region superficial to the supra-hyoid strap muscles. It contained numerous T1/T2 hyperintense round lesions.

FIG 6A & 6B

T1WI fat-saturation without (A) and with (B) gadolinium based contrast axial sections of MRI neck showed no suppression of the T1 hyperintense lesions within the cyst on fat-saturation and no contrast enhancement of the lesions or the cyst.

FIG 7A & 7B

DWI and ADC map axial sections of MRI neck showed diffusion restriction of the lesions within the cyst with corresponding drop-out on ADC map suggesting true diffusion restriction.

FIG 8A & 8B

Intra-operative (A) and gross specimen (B) images of the cyst removed by surgical excision. 

Radiological diagnosis:  

Subcutaneous epidermal inclusion cyst of the neck

Pathological diagnosis:

Epidermal inclusion cyst

Management:

The cyst was removed by surgical excision.

Discussion

Epidermoid or epidermal inclusion cysts are formed by the proliferation of epidermal cells within a defined dermal space. The epidermoid cyst can occur at any age, but it is more frequent in adulthood [1]. They are predominantly found in males. Approximately 1% of epidermoid cysts have been noted to have a malignant transformation to squamous cell carcinoma and basal cell carcinoma [1,2]

The face, neck, periauricular area, and upper trunk are more commonly involved, but any part of the body including sites such as the nipple, genitalia, and palmoplantar area may be involved.

 These differ from dermoid cysts due to a lack of dermal appendages. [3] These are unilocular cysts which show posterior acoustic enhancement, no septations and are surrounded by a fibrous tissue capsule. The cyst content is formed by the accumulation of cutaneous products within an enclosed space consisting of keratin, protein, cholesterol, and cell membrane lipids. [3,4]. The amount and arrangement of the keratin and other debris determines the radiological appearance of the cyst which can hence be diverse. [5] Commonly floating linear echogenic reflections are seen, caused by layered and aggregated keratin debris, with interspersed dark clefts due to areas lacking keratin. On ultrasound examination, dermoid cysts typically show a heterogeneous appearance which may be seen due to the presence of echogenic fat, osseous, or dental elements. [6] Sometimes, due to the coalescence of fat into small nodules within the cystic lesion, a “sac-of-marbles” appearance is seen on US. In the case discussed above, a similar appearance was noted in the submandibular cystic lesion on US which mimicked the appearance of a dermoid cyst. However no calcifications were noted on US.

On MR, epidermoid cysts show a high T2 signal background along with internal low T2 and high T1 foci within- which correspond to the keratinous aggregates in the cyst and hence, do not show a signal drop on fat-suppressed T1 weighted images [7]. On the contrary, dermoid cysts containing fat-rich elements which appear T1 and T2 hyperintense compared to the subcutaneous fat layer, also appear hypointense on fat suppressed T1 WI. [8] In our case, the ‘marbles’ in the “sac-of-marbles” appearance of the cyst, that is, the globular aggregates which were T1 hyperintense did not show a signal drop on fat suppression along with true diffusion restriction- pointing more towards keratinous/proteinaceous aggregates rather than fat globules and hence, leaning more towards epidermoid cyst as the radiological diagnosis.

Small uncomplicated cysts usually do not need treatment. For larger cysts, removal may be accomplished by simple complete surgical excision of the cyst with the cyst wall intact.

References:

1.Mendonca de J. Jardim E. Dos Santos C. Masocatto D. Quadros de D. Oliveira M. et al. Epidermoid cyst: clinical and surgical case report. Ann. Maxillofac. Surg. 2017; 7: 151-154

2. Zito P. Schar F.Cyst  Epidermoid (Sebaceous Cyst). Treasure Island (FL). StatPearls Publishing, 2019

3. Mittal MK, Malik A, Sureka B, Thukral BB. Cystic masses of neck: a pictorial review. Indian Journal of Radiology and Imaging. 2012 Oct;22(04):334-43.

4. Lever WF, Lever GS. Tumor and cysts of epidermis. In: Elder D, editor. Histopathology of the skin. 8th ed. Philadelphia, JB: Lippincott, 1997, p. 685-746

5. Elder D, Elenitsas R, Jaworsky C, Johnson Jr B. Lever’s histopathology of the skin. 8th ed. Philadelphia: Lippincott Raven; 1997. p. 695–721.

6. Langer JE, Ramchandani P, Siegelman ES, Banner MP. Epidermoid cysts of the testicle: Sonographic and MR imaging features. Am J Roentgenol. 1999;173(5):1295–9.

7. Kim HK, Kim SM, Lee SH, Racadio JM, Shin MJ. Subcutaneous epidermal inclusion cysts: ultrasound (US) and MR imaging findings. Skeletal radiology. 2011 Nov;40:1415-9.

8. Chung BM, Kim WT, Park CK, Kim MA. Dermoid cyst in the subcutaneous tissues of the back: A rare case with multimodal imaging and pathologic correlation. Radiology Case Reports. 2021 May 1;16(5):1127-32.