Parosteal lipoma of the mandible Martin Steiner, D.D.S., * Alan R. Gould, D.D.S., MS., ** James Rasmussen, D.M.D., *** and Daniel LaBriola, D.D.S.,**** Louisville, Ky.

UNIVERSITY OF LOUISVILLE SCHOOL OF DENTISTRY

The parosteal lipoma represents an uncommon benign neoplasm which usually affects the long bones. An example of parosteal lipoma involving the body of the mandible, which was incidentally discovered on roentgenographic examination, is described. This represents the first reported example affecting the jaws. Benign lipomatous involvement of bone is also reviewed.

L ipomas occurring in the soft parts constitute one of the more commonly encountered types of benign neo- plasm. Within the oral cavity, the lipoma is distinctly rarer, representing about 1 per cent of all benign oral tumors in the Armed Forces Institute of Pathology files.’ Though generally limited to the soft tissues, a significant number of lipomas affecting bone have been reported,* with three forms being specifically defined.3 These are (1) the intraosseous lipoma, arising within the medullary cavity of the bone and expanding from within, (2) the parosteal lipoma, which exhibits a con- tiguous relationship with the periosteum, usually dem- onstrating some form of attachment to periosteum with an underlying osseous reaction, and (3) the soft-tissue lipoma which, though it may mimic the parosteal lipoma when it occurs near a bone, only secondarily involves the bone by pressure or direct invasion.

The intraosseous lipoma is a very rare tumor. Hart* reviewed the world literature in 1973 and reported 28 cases; DeLee,3 in 1979, added five additional cases. The sites of involvement included the long bones (50 per cent), along with the calcaneus, ribs, distal phalanx of the thumb, frontal, parietal, and sacral bones, as well as four tumors in the jaws. Of this latter group, three were found in the mandible4-6 and one in the maxilla.’ A further search of the literature revealed three additional cases affecting the maxilla.s-10

The parosteal lipoma appears somewhat more com- mon than its intraosseous counterpart, with more than 100 cases documented in the world literature. A variety of bones reportedly have been involved, including the

*Associate Professor; Department of Oral and Maxillofacial Surgery. **Assistant Professor, Department of Oral Pathology/Pathology. ***Senior Resident, Department of Oral and MaxiIlofacial Surgery. ****Former Senior Resident, Department of Oral and Maxillofacial Surgery.

0030-4220/81/070061+05$00.50/0 @J 1981 The C. V. Mosby Co.

Fig. 1. Segment of Panorex roentgenogram demonstrating a well-defined radiolucency in the posterior right mandible in- volving the crestal bone of the body and anterior ramus.

long bones, ribs, skull, scapula, metatarsal, metacar- pal, vertebral column, clavicle, and pelvis.” No cases of parosteal lipoma of the mandible or maxilla have been reported as such in the literature, although exam- ples of lipoma have been described in close association with the oral osseous structures occurring in gin- giva1*-16 and hard palatal mucosa.17-1g

Clinically, the parosteal lipoma generally presents as a slowly enlarging but otherwise asymptomatic mass. However, compression of adjacent structures, such as nerves, has been reported, resulting in functional deficits.*O-*I Fleming, Alpert, and Garcia,” in their review of parosteal lipoma, outlined the roentgeno- graphic and surgical characteristics of this lesion. The roentgenographic appearance is that of an encapsu- lated, smooth-surfaced, soft-tissue mass which lies in close relationship to an adjacent bone. Underlying os- seous cortical responses vary, ranging from a reactive overproduction of bone to cortical erosion. Osseous bowing has also been reported as a response of bone to

61

62 Steiner et al. Oral surg. July, 1981

Fig. 2. Photomicrograph of parosteal lipoma demonstrating lobules of adipose tissue with delicate fibrous connec- tive tissue septa. (Hematoxylin and eosin stain. Original magnification, x2.5.)

the overlying parosteal lipoma. The surgical finding is that of an encapsulated, sometimes bosselated, well- defined, yellow mass which demonstrates a broad base of attachment to the periosteum of the underlying bone. Removal of the lesion generally entailed sharp dissec- tion from the periosteum with curettes, leaving behind seemingly thickened periosteum. However, in a sig- nificant minority of cases, the lesion displayed little or no attachment to the underlying periosteum. Occa- sionally the lipoma was associated with proliferation of bone arising from the underlying cortex. In these in- stances, the use of chisels was required to free the mass.

The light microscopic features of the parosteal lipoma have, in general, been similar to those of its soft-tissue counterpart, consisting of lobules of mature lipocytes with either prominent or minimal amounts of interlobular fibrous connective tissue.“, 21--25 A fibrous capsule has been described relative to this lesion22 and, in distinction to the soft-tissue lipoma, occasional close association between benign neoplastic adipose tissue and mature trabeculae of bone derived from an underly- ing hyperostotic response has been noted.22* 24 Reactive bone has also been described in association with parosteal lipoma. l1

Recently, a patient presented to the Oral and Maxil- lofacial Surgery Outpatient Clinic of the Louisville General Hospital for treatment of a mandibular frac- ture . During evaluation and examination of this patient, a lesion was encountered in the right posterior mandi- ble, and the clinical, roentgenographic, surgical, and histologic findings, when taken together, strongly sug-

gested the diagnosis of parosteal lipoma. Given the interest in this case, its unusual roentgenographic fea- tures, and the fact that parosteal lipoma has not previ- ously been reported in the jaws, it was felt desirable to report this case.

CASE REPORT

A 50-year-old black man presented to the Oral and Maxil- lofacial Surgery Outpatient Clinic of Louisville General Hospital on May 3 1, 1979, with a chief complaint of pain and swelling of the anterior part of the mandible. The patient stated that he had been involved in a motor vehicle accident 4 weeks previously, striking his chin on the dashboard. The patient received no other bodily injury, did not suffer loss of consciousness, and did not seek immediate treatment at the time of the accident.

During the subsequent 3 weeks, the patient noticed exter- nal swelling at the left parasymphysis area associated with drainage of a foul-smelling material intraorally and a marked increase in pain.

Past medical history revealed that the patient was a chronic alcohol abuser and had previously been treated for hyperten- sion with Esidrix and Aldomet. The blood pressure on ad- mission was 180/ 120 mm Hg . The remainder of the physical examination, except for a mandibular fracture, was essen- tially within normal limits. The patient was placed on Oretec, (50 mg. twice a day), which resulted in a blood pressure of 12OBO. He was subsequently to be followed by the General Medical Clinic after discharge from the hospital.

Clinical examination of the oral cavity revealed severe periodontal disease involving the remaining dentition with an obvious fracture of the mandible between the left canine and lateral incisor. There was purulent drainage at this site. Moderate induration was detected in the submental area with

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Parosteal lipoma of the mandible 63

Fig. 3. Photomicrograph of parosteal lipoma demonstrating mature lipocytes with peripherally displaced flattened nuclei and minimal cytoplasmic contents. (Hematoxylin and eosin stain. Original magnification, X 100.)

Fig. 4. Photomicrograph of parosteal lipoma showing fibrous connective tissue capsule. (Hematoxylin and eosin stain. Original magnification, X25.)

associated lymphadenopathy. The maxilla was intact and the clinical appearance of the intraoral soft tissues was otherwise unremarkable.

Roentgenographic examination revealed a left parasym- physis fracture. An incidental roentgenographic finding was a 2.0 by 1.5 cm. well-circumscribed, somewhat cystic-appear- ing radiolucent lesion of the posterior right mandible (Fig. 1). The lesion extended from the mandibular crest and anterior ramus down into the mandible, presenting a scooped-out ap- pearance. On its inferior and distal aspects, the radiolucency

was bordered by a smooth, sclerotic bony margin. This mar- gin appeared to be continuous distally with the anterior cortex of the mandibular ramus. The lesion was closely associated anteriorly with the distal root of the erupted third molar. No cortical margin of bone was roentgenographically evident overlying the radiolucency. Clinical re-examination of the mandibular right third molar region failed to reveal any ex- pansion. The surrounding gingival tissue was normal in color and texture, and there was no increase in mobility of the third molar. The patient was unaware of the presence of the lesion.

64 Steiner et al. oral Slug. July, 1981

With a provisional diagnosis of odontogenic cyst, the pa- tient was taken to the operating room on June 5, 1979, and general anesthesia was induced through a nasotracheal tube. With the patient prepared and draped in the usual manner, the mandibular right second and third molars were removed by means of simple forceps technique. A periosteal flap was raised, and it was noticed that there was a 1.5 cm. mass lying within a bony crypt distal to, but associated with, the extrac- tion socket of the third molar. The tumor was adherent to the overlying mucosal flap and was curetted from the adjacent tissue with some difficulty. The mass appeared to shell out easily from the bony cavity and was not adherent to the under- lying periosteum, leaving a smooth bony cavity. The area was irrigated and the soft tissue flap was closed with 3-O Dexon sutures. Arch bars were then placed on the remaining maxil- lary and mandibular teeth for the treatment of the mandibular fracture. The patient was placed in intermaxillary fixation and taken to the recovery room.

Microscopic findings

Histologic examination revealed sections of tissue which were composed of a benign proliferation of adipose tissue in association with dense fibrous connective tissue and viable woven bone. The adipose tissue was arranged in several lobules, separated by delicate septa of fibrous connective tis- sue (Fig. 2). These connective tissue septa were composed of coarse collagenous bundles with fibrocytes, fibroblasts, and endothelium-lined vascular structures filled with red blood cells. The adipose tissue was composed of mature lipocytes exhibiting peripherally displaced, flattened nuclei with little if any cytoplasmic elements (Fig. 3). About the periphery of the tissue was a well-formed fibrous connective tissue capsule (Fig. 4). Portions of this capsular tissue were found in asso- ciation with trabeculae of woven bone. The capsule supported a patchy, dense, chronic inflammatory cell infiltrate of Iym- phocytes, macrophages, and occasional polymorphonuclear leukocytes. Several small blood vessels exhibited extensive intimal thickening. The histologic findings, when combined with the clinical and roentgenographic features, were consis- tent with the diagnosis of parosteal lipoma.

DISCUSSION

This case represents the first reported example of intraoral parosteal lipoma. In analyzing the case, it is useful to make comparisons with previously reported examples affecting extraoral sites. Fleming, Alpert, and Garcia” have summarized the features which characterize the parosteal lipoma. In their series sixteen cases displayed a firm attachment to bone at surgery, four were loosely adherent, three had loose and firm attachment, and two had no attachment to bone. Our case did not exhibit any adherence to the underlying bone or periosteum. In their review” it was found that sixteen of twenty-seven cases had associated bony al- terations on roentgenographic examination, with eleven cases specifically exhibiting a hyperostotic reaction. Our case showed a marked radiolucent depression ex-

tending into the crestal bone of the mandible with a very well-defined hyperostotic response. Our patient had no symptoms, and a similar absence of symptoms was noted in ten of twenty-nine cases previously re- viewed.” Bick2” has also discussed this lesion, includ- ing as characteristic features the creation of a flattened depression in the underlying bony cortex without any evidence of frank invasion. Though a deformation is produced in the surface of the bone, the cortex remains intact. Our case exhibited similar features.

The histologic features in the present case embody elements similar to those previously reported for the parosteal lipoma. In addition to the presence of mature adipose tissue and fibrous connective tissue septa, the identification of a fibrous capsule and the association with reactive bone comprise previously reported fea- tures for this lesion. l*, 22

A limited number of intraoral lipomas have been described affecting soft tissues directly adjacent to bone. Specific sites involved were the gingiva12-‘” and hard palatal mucosa. Ii-l9 In all of these cases, the le- sion clinically presented as a soft tissue mass. Further, in nearly every instance no alterations in the underlying bony structures were described. The single exception to this latter statement is the report of Christensen,15 in which a slight amount of resorption was noted in the maxilla beneath the overlying soft tissue mass. How- ever, the presence of an ill-fitting denture over the mass might well have contributed to the underlying mild re- sorption. In the present case, no clinical soft-tissue mass was detectable preoperatively; nor were there any associated symptoms. The roentgenographic alterations in the mandible comprised the sole basis for the lesion’s detection, and the preoperative diagnosis was based upon the assumption that the lesion was essentially in- traosseous. The surgical findings, however, suggested that the lesion arose in close relationship with the mandibular periosteum and that its growth pattern was such as to create a depression in the bone rather than expanding outward into the soft tissue. The underlying cortical hyperostotic response reflected this pattern of lesional expansion.

The clinical and surgical features in the present case are considered sufficiently distinctive to separate the case from examples of extraosseous, intraoral lipoma previously reported in close association with the sur- face of a bone. Further, our case shares a number of features with the parosteal lipoma as reported in ex- traoral sites. It is therefore concluded that the present case represents an example of an intraoral parosteal lipoma .

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Reprinr requests IO:

Dr. Martin Steiner Department of Oral and Maxillofacial Surgery School of Dentistry University of Louisville Health Sciences Center Louisville, Ky 40292