# Intraosseous Epidermoid Cyst of Distal Phalanx of Fingers

Authors: Chih-Hsin Hsieh; Yin-Chun Tien; Song-Hsiung Chien
Journal: Scholarly Research Exchange
 (2008)

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## Abstract

Intraosseous epidermoid cysts of fingers are uncommon lesions. We reported two cases with intraosseous epidermoid cysts of distal phalanx of fingers. Case 1 was a 61-year-old woman with a swelling of the left middle finger without history of trauma. Case 2 was a 47-year-old male with a crushing injury of his right thumb. On radiographic findings, a well-circumscribed osteolytic lesion in distal phalanges was noted. Unexpectedly, histological examinations showed intraosseous epidermoid cyst.


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## Body

## 1. Introduction

Epidermoid  cysts are commonly found
in the subcutaneous tissue of the entire body, but intraosseous epidermoid
cysts are unusual. Intraosseous epidermoid cysts arise most frequently in the
skull and the distal phalanges of the hand [1–3]. It is  very difficult to diagnose
them correctly before surgery according to
clinical and radiographic findings.
We reported two cases with intraosseous epidermoid cysts of fingers and discussed
the origins of the tumor.


## 2. Case Presentation

### 2.1. Case 1

A 61-year-old
woman came to our clinic due to a swelling of left middle finger tip for 2
months. Tracing her history, no trauma occurred and the swelling developed
gradually without tenderness. Erythema of finger tip was found. Roentgenograms
demonstrated a well-defined osteolytic lesion over distal phalanx of the left
middle finger (Figure1). Magnetic resonance imaging (MRI) showed a
well-defined osteolytic nodule beneath the nail of left middle finger (Figure
2). Under the impression of enchondroma or glomus tumor, surgical intervention
was undertaken. Unexpectedly, a well-encapsulated cyst was discovered with
grayish stinky material inside. Curettage of the cyst was performed. The
pathologic examination demonstrated epidermoid cyst with granulation formation
and foreign body reaction in the adjacent tissue (Figure 3).Figure 1
Roentgenogram of left middle finger showing a well-defined osteolytic lesion in
the distal phalanx.Figure 2
Magnetic resonance
imaging of left middle finger showing a well-defined nodule and erosion of bone
under the nail.Figure 3
Laminated
keratin in the cyst lined by stratified squamous epithelium. (Hematoxylin-eosin stain, original
magnification, 20×).


### 2.2. Case 2

A 47-year-old
male got a crushing injury of right thumb 2 years ago. He recovered quickly
with normal thumb function; but right thumb pain was noted 6 months later. In
physical examination, a reddish subungual patch was noted. Radiographic study
showed a radiolucent intraosseous lesion in the distal phalanx of his right
thumb (Figure4). During the operation, a well-encapsulated cyst with white
chessy material was discovered. After enucleation of the cyst, filling the
defect with autogenous bone graft harvested from ipsilateral distal radius was
done (Figure 5). The pathologic examination revealed laminated keratin in the
cyst lined by stratified squamous epithelium consistent with epidermoid cyst.Figure 4
Radiograph of right thumb
showing an osteolytic lesion with bony defect and fracture in the distal
phalanx.Figure 5
Radiograph of right thumb
after curettage of the cyst and filling the defect with autogenous bone graft
from ipsilateral distal radius.


## 2.1. Case 1

A 61-year-old
woman came to our clinic due to a swelling of left middle finger tip for 2
months. Tracing her history, no trauma occurred and the swelling developed
gradually without tenderness. Erythema of finger tip was found. Roentgenograms
demonstrated a well-defined osteolytic lesion over distal phalanx of the left
middle finger (Figure1). Magnetic resonance imaging (MRI) showed a
well-defined osteolytic nodule beneath the nail of left middle finger (Figure
2). Under the impression of enchondroma or glomus tumor, surgical intervention
was undertaken. Unexpectedly, a well-encapsulated cyst was discovered with
grayish stinky material inside. Curettage of the cyst was performed. The
pathologic examination demonstrated epidermoid cyst with granulation formation
and foreign body reaction in the adjacent tissue (Figure 3).Figure 1
Roentgenogram of left middle finger showing a well-defined osteolytic lesion in
the distal phalanx.Figure 2
Magnetic resonance
imaging of left middle finger showing a well-defined nodule and erosion of bone
under the nail.Figure 3
Laminated
keratin in the cyst lined by stratified squamous epithelium. (Hematoxylin-eosin stain, original
magnification, 20×).


## 2.2. Case 2

A 47-year-old
male got a crushing injury of right thumb 2 years ago. He recovered quickly
with normal thumb function; but right thumb pain was noted 6 months later. In
physical examination, a reddish subungual patch was noted. Radiographic study
showed a radiolucent intraosseous lesion in the distal phalanx of his right
thumb (Figure4). During the operation, a well-encapsulated cyst with white
chessy material was discovered. After enucleation of the cyst, filling the
defect with autogenous bone graft harvested from ipsilateral distal radius was
done (Figure 5). The pathologic examination revealed laminated keratin in the
cyst lined by stratified squamous epithelium consistent with epidermoid cyst.Figure 4
Radiograph of right thumb
showing an osteolytic lesion with bony defect and fracture in the distal
phalanx.Figure 5
Radiograph of right thumb
after curettage of the cyst and filling the defect with autogenous bone graft
from ipsilateral distal radius.


## 3. Discussion

In 1968, Lerner and Southwick [1] reported that the
intraosseous epidermoid cysts were twice as common in men as in women whose
ages range between 8 and 83 years, and they tended to be concentrated in adults
between the ages of 25 and 50 years—most common especially
in actively working people. In 1970, Schajowicz et al. [4]
cited that men are predominated
and that the age of onset of the disease was between 19 and 54 years. The
majority were manual workers and the most common location was the end phalanx
of the hand. The left hand has a higher incidence of cysts than the right with
the left middle finger being the most common site. The thumb, index, and ring
finger are the next most common sites [1, 2].
Additional sites of involvement include phalanges of toes and large toe, ulna,
femur, tibia, sternum, and amputation stumps
[1, 3–5].
The symptoms comprise an increase in finger size with, or without pain and
tenderness, redness, and curving of the nail. The interval between the trauma
and the appearance of symptoms varies from weeks to years
[1, 2, 4].Epidermoid cysts of the skull are
slow growing and are sometimes detected accidentally on radiographic
examination of the skull. Most cases arise on the accessory sinus of the nose
and occipital scalp. Headache is the most frequent symptom. The cause of
punched-out bony defect of the skull is thought to be long-term continuous
pressure by the cyst resulting in the bone defect called scalloping
[6].The radiographic findings of
intraosseous epidermoid cysts are not diagnostic. Roentgenograms show a
well-defined osteolytic lesion frequently outlined by a thin rim of sclerotic
bone. When the lesion reaches a certain size, the cortex becomes expanded and
thinned, and the fractures or the bony defects may be observed
[1, 4].
The differential diagnosis includes enchondroma, glomus tumor, aneurysmal bone
cyst, metastasis, and osteomyelitis. Enchondroma is the most common and
destructive primary bone tumor of the hand, and occurs more commonly in the
middle and proximal phalanges. Unlike intraosseous epidermoid cysts, glomus
tumors cause severe pain, cold sensitivity, and point tenderness. Glomus tumors
produce pressure erosion and demonstrate smooth, concave deformity at one side
or on the dorsum of the phalanx beneath the fingernail, or as a punched-out
defect in the tuft. In the aneurysmal bone cyst, the eccentric bulb-like lesion
occurs in the metaphysis of tubular bone, causing pain and limitation of motion.
The sharp edge of an epidermoid cyst is distinctly different from the poorly
defined osteolytic lesions observed with osteomyelitis and metastatic disease
[1, 2, 4].
So, it is difficult to differentiate these tumors according to radiographic
findings. Histological examination is the only way for accurate diagnosis.Macroscopically, the cystic
unilocular cavity of intraosseous epidermoid cysts reaches a diameter from 1 to
20 mm. The outer membrane is 1
to 5 mm thick and easily
separated from the surrounding bone [4].
Histological examination demonstrates a cyst wall with stratified squamous
epithelium with a well-defined granulous layer covered by laminated masses of
keratin. While the cyst wall is interrupted and the keratin masses come into
direct contact with the pericystic connective tissue, the foreign-body and
giant-cell granuloma will germinate. The cyst contents comprise keratin,
foreign-body giant cells, cholesterol cleft, and chronic inflammatory cells.
There is no histologic difference between anatomic locations
[2, 4].The etiologies of phalangeal
epidermoid cysts are thought to be (1) traumatic and being secondary to
implantation of epidermal elements into the bone [1–5, 7, 8], (2) blastomatous formations, originating from displaced neural tube
epithelial cell remnants during embryonic development
[2, 6],
or (3) iatrogenic origin related to a previous surgery, such as amputation
stump [4].
In 2003, Ambo et al. [6] described a case of
epidermoid cyst with perforation of the skull, and hypothesized that long-term
continuous pressure by the cyst resulted in a bone defect. In case 2, the cause
is believed to be due to traumatic introduction of epidermal tissue into bone.
However, no trauma history was noted in Case 1 and there was no prior surgical
history. Therefore, the cause of the lesion is hypothesized to be ectodermal
cell rests during embryonic development.In intraosseous epidermoid cysts, curettage
with or without bone grafting is adequate. Amputation should not be performed
as a primary treatment
[1, 2, 4, 5].
The clinical symptoms and radiological findings of intraosseous epidermoid
cysts are nonspecific. It is challenging to differentiate intraosseous
epidermoid cysts from other bone tumors of hands. Histological examination is
very important for accurate diagnosis of intraosseous epidermoid cyst. In
conclusion, the physicians should recognize the entity, and the intraosseous
epidermoid cyst should be included in the differential diagnosis of bone tumors
of hands. Histological examination should be performed as early as possible for
correct diagnosis and appropriate managements.



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*Source: 963687-2008-12-25.xml*