Page 57 - The Netter Collection of Medical Illustrations - Integumentary System_ Volume 4 ( PDFDrive )

Plate 2-30 Benign Growths

OSTEOMA CUTIS

Painless bony mass protrudes from
Osteoma cutis is a rare benign tumor in which bone anterior aspect of tibia. Scars due
formation occurs within the skin. There are two types to repeated skin abrasions
of osteoma cutis, primary and secondary. Primary
osteoma cutis is idiopathic in nature, whereas secondary
osteoma cutis is caused by bone formation in an area of
trauma or another form of cutaneous inflammation. It
can also be seen secondary to abnormalities of parathy-
roid hormone metabolism, and this form of osteoma
cutis is called metastatic ossification. Secondary osteoma
cutis is much more common than the primary idio- Radiograph reveals globular outgrowth on tibial
pathic form. cortex with sloping extensions (Codman’s triangles)
Clinical Findings: Primary osteoma cutis is not asso- Specimen demonstrates continuity
ciated with any defined underlying disorder and can of tumor with overlying periosteum.
manifest as a solitary nodule, plaque, or plate-like hard-
ening of the skin. Some are quite small, whereas others
are large and cause discomfort. Males and females are
equally affected, and there is no race predilection. The
age at onset is variable. Plate-like or plaque-like osteoma
cutis is a form of primary osteoma cutis that occurs
during the first few months of life and can even be
present at birth. The acral regions are most commonly
affected. Over time, these osteomas tend to develop
ulcerations or erosions of the overlying epidermis.
With this ulceration, small parts of the osteoma are
extruded from the underlying dermis and expelled
from the skin. This may be the cause for presentation
to the clinician. Most patients present with a thickened
or hardened area of skin with no preceding trauma Radiograph of excised tumor reveals
or inflammatory condition. There is no malignant densely ossified cortical mass protruding
potential. from outer table of skull.
Primary osteomas of the skin may be seen in the
genetically inherited disease, Albright’s hereditary
osteodystrophy. This condition is characterized by a Slowly enlarging, asymptomatic
constellation of findings including short stature, bony mass on dome of head
osteoma cutis, mental and physical delay, and brachy-
dactyly. Varying degrees of obesity and a round appear-
ance to the face are also seen. This condition is caused
by an underlying defect in the GNAS gene. This gene High power. A well-
encodes a stimulatory G protein (G s ) that is responsible circumscribed nodule
for cell signaling through the eventual production of of bone formation just
cyclic adenosine monophosphate (cAMP). Albright’s underneath the epidermis.
hereditary osteodystrophy has been reported to mani- A few haversian canals
fest with resistance to parathyroid hormone, but other are present.
Albright’s patients have not shown this resistance.
These differences are likely due to the complex
inheritance pattern and whether the defective gene
was inherited from the maternal or paternal side or underlying tissue. This disease is progressive and can formed by an intramembranous mechanism without the
both. Most patients have associated hypocalcemia and result in premature death. This condition is unique in assistance of a preceding cartilage scaffolding.
hyperphosphatemia. that it is caused by endochondral bone formation. Treatment: Secondary osteoma cutis can be removed
Secondary osteoma cutis is far more common than Pathogenesis: Primary forms of osteoma cutis show with a number of surgical techniques. Creation of a
the primary form, by a ratio of about 9 : 1. Bone forma- intramembranous ossification that is centered within small, nick-like incision over the area of osteoma for-
tion may occur in any area of previous skin trauma, acne the dermis. There is no preceding cartilage formation mation and removal with a small curette or laser resur-
cysts, or epidermal inclusion cysts and are commonly to act as a scaffolding for the bone to form. The exact facing has produced the best results. This treatment can
seen in pilomatricomas. Pilomatricomas are benign cause is unknown. The G protein that is defective be very time-consuming and labor intensive in cases of
tumors that most often manifest in childhood. Inflam- in Albright’s hereditary osteodystrophy has been multiple secondary osteoma cutis (e.g., in some cases of
matory conditions associated with osteoma cutis include found to be important in bone regulation. The precise acne-associated osteoma cutis).
dermatomyositis and scleroderma. reason why some areas of skin are involved while others The treatment of primary plaque-like osteoma cutis
Fibrodysplasia ossificans progressiva is a rare genetic are left intact in this genetic disease is not well is surgical removal. Albright’s heriditary osteodystrophy
condition in which connective tissue is turned into bone understood. and fibrodysplasia ossificans progressiva are rare dis-
after minor trauma, causing secondary osteomas. The Histology: Areas of bone formation are seen ectopi- eases that require a multidisciplinary approach at
skin can be involved, but so can the muscle and other cally in the dermis or subcutaneous tissue. The bone is centers with experience treating these conditions.

THE NETTER COLLECTION OF MEDICAL ILLUSTRATIONS 43