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Apparent Diffusion Coefficient of Subcutaneous Epidermal Cysts in the Head and Neck

Posted Aug 31, 2007 Updated Apr 7, 2023
By Chiori Suzuki MD , Masayuki Maeda MD , Akihiko Matsumine MD , Toshio Matsubara MD , Waro Taki MD , Stephan E. Maier MD PhD , Kan Takeda MD
8 min read

Rationale and Objectives

Subcutaneous epidermal cysts and intracranial epidermoid cysts are pathologically identical. Although diffusion-weighted imaging (DWI) studies of intracranial epidermoid cysts have been numerously reported, those of subcutaneous epidermal cysts have not been sufficiently investigated. Our hypothesis for this study is that the apparent diffusion coefficient (ADC) values of subcutaneous epidermal cysts and intracranial epidermoid cysts are not different. This study was intended to evaluate the ADC of subcutaneous epidermal cysts of the head and neck in comparison with that of intracranial epidermoid cysts.

Materials and Methods

The MR studies were performed in 14 patients with head and neck subcutaneous epidermal cysts and 10 patients with intracranial epidermoid cysts using line scan DWI (LSDWI). The ADC was measured and compared between the two types of cyst.

Results

The ADC values (mean ± SD) were 0.81 ± 0.14 × 10 −3 mm 2 /s in subcutaneous epidermal cysts and 1.06 ± 0.12 × 10 −3 mm 2 /s in intracranial epidermoid cysts. A significant difference was found in ADC values between the two types ( P = .0019).

Conclusion

Our preliminary study has shown that the ADC provides useful information regarding tissue characterization of subcutaneous epidermal cysts. However, the ADC of subcutaneous epidermal cysts was significantly lower than that of intracranial epidermoid cysts.

Epidermal cysts are common, benign masses that occur in the skin. The lesions commonly involve the scalp, face, neck, trunk, and back ( ). However, only a few reports regarding MR imaging findings have been issued on subcutaneous epidermal cysts ( ). Typical MR imaging findings of subcutaneous epidermal cysts include a well-circumscribed margin, iso-, or slightly high signal intensity relative to adjacent muscles on T1-weighted images, and very high signal intensity on T2-weighted images ( ). Usually, no apparent enhancement is visible inside the cyst if unruptured ( ).

Subcutaneous epidermal cysts and intracranial epidermoid cysts are pathologically identical: cysts filled with keratin debris and bounded by a wall of the stratified squamous epithelium ( ). Unlike subcutaneous epidermal cysts, numerous MR imaging reports have described intracranial epidermoid cysts ( ). Several studies of diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) have had particular impact on the diagnosis of the intracranial epidermoid cysts ( ). However, reports on DWI and ADC of subcutaneous epidermal cysts are insufficient. We hypothesize that ADC values of subcutaneous epidermal cysts and intracranial epidermoid cysts are not different because they are pathologically identical. This study was intended to evaluate the ADC of subcutaneous epidermal cysts of the head and neck in comparison with that of intracranial epidermoid cysts.

Materials and methods

Subjects

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MR Imaging

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Imaging Data Analysis

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Figure 1, A 52-year-old woman with intracranial epidermoid cyst in her left cerebellopontine angle cistern. T1-weighted ( a ) and T2-weighted ( b ) images show a mass that is equivalent to the signal intensity of cerebrospinal fluid. ( c ) 3D heavily T2-weighted image reveals that the lesion contains intervenient cerebrospinal fluid. ( d ) ADC map shows higher diffusion of the lesion than that of the adjacent normal brain. Note the heterogeneity of the ADC inside the lesion. The ADC of the lesion ( circled area ) is 1.14 × 10 −3 mm 2s. The ADCs of adjacent cerebellum and pons are 0.70 and 0.82 × 10 −3 mm 2s, respectively. ( e ) Photomicrograph shows keratin debris ( arrow ) and a wall of the stratified squamous epithelium.

Figure 2, A 56-year-old man with intracranial epidermoid cyst in the fourth ventricle. T1-weighted ( a ) and T2-weighted ( b ) images show a mass that is equal to the signal intensity of cerebrospinal fluid, but the internal texture of the epidermoid cyst is slightly heterogeneous. ( c ) 3D heavily T2-weighted image reveals that the mass contains intervenient cerebrospinal fluid. ( d ) ADC map shows slightly increased diffusion of the epidermoid cyst compared with that of adjacent normal brain. Note the heterogeneity of the ADC inside the lesion. The ADC of the mass ( circled area ) is 0.89 × 10 −3 mm 2s. The ADC of the adjacent cerebellum is 0.71 × 10 −3 mm 2s.

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Statistical Analysis

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Results

Signal Intensities and Contrast Enhancement of the Lesions

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Table 1

MR Imaging Findings of Subcutaneous Epidermal Cysts and Intracranial Epidermoid Cysts

Imaging Findings Subcutaneous Epidermal Cyst ( n = 14) Intracranial Epidermoid Cyst ( n = 10) Signal intensity (T1-weighted) Low 0 9 High 14 0 Mixed 0 1 Signal intensity (T2-weighted) Low 3 0 High 9 10 Mixed 2 0 Contrast enhancement No enhancement 5 8 Thin and smooth rim 4 0 NA 5 2

NA, not applicable.

Figure 3, A 58-year-old woman with subcutaneous epidermal cyst in her right cheek. ( a ) T1-weighted image shows that a subcutaneous epidermal cyst ( arrow ) in her right cheek is slightly higher in signal intensity than cerebrospinal fluid. Note a parotid tumor (subsequently confirmed as pleomorphic adenoma) shown on the right. ( b ) T2-weighted image shows that the signal intensity of the mass is equivalent to that of cerebrospinal fluid. ( c ) Contrast-enhanced T1-weighted image shows no enhancement of the subcutaneous epidermal cyst. However, the parotid tumor enhances strongly. ( d ) The ADC map shows lower diffusion of the subcutaneous epidermal cyst than that of the parotid mass. The ADC of subcutaneous epidermal cyst is 0.85 × 10 −3 mm 2s, whereas that of parotid tumor is 1.25 × 10 −3 mm 2s. ( e ) Photomicrograph shows keratin debris and a wall of the stratified squamous epithelium.

Figure 4, A 65-year-old man with subcutaneous epidermal cyst in his neck. ( a ) T1-weighted image shows that the signal intensity of the subcutaneous epidermal cyst (arrow) at the neck is almost equal to that of adjacent muscle. ( b ) T2-weighted image shows that the signal intensity of the mass is markedly high. ( c ) Contrast-enhanced T1-weighted image shows no enhancement of the epidermal cyst. ( d ) LSDWI image ( b = 1000 s/mm 2 ) shows a bright signal of the epidermal cyst compared with that of adjacent muscle. ( e ) On ADC map, the ADC of the epidermal cyst is 0.76 × 10 −3 mm 2s.

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ADC Values

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Figure 5, Box plot of the ADC in subcutaneous epidermal cysts and intracranial epidermoid cysts. The ADC of subcutaneous epidermal cysts is significantly lower than that of intracranial epidermoid cysts ( P = .0019).

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Discussion

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Conclusion

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Academic Radiology, Volume 14, Issue 9
Journals General Radiology
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