De novo subgaleal abscess.

The authors report a case of spontaneous subgaleal abscess formation in a 62-year-old woman without antecedent trauma or injury. She presented with occipital scalp pain and swelling which rapidly became generalized two days following recovery from an upper respiratory infection. Diagnosis was based on radiological examination and aspiration of the subgaleal space, which yielded a purulent exudate with a pure growth of Streptococcus pyogenes. Initial management with incision, drainage and parenteral antimicrobial therapy was not successful. Operative exploration of the subgaleal space revealed extensive necrosis of the galea aponeurotica, and bone curettings revealed microscopic evidence compatible with osteomyelitis. Management with debridement and excision of all necrotic tissue plus prolonged parenteral antimicrobials was successful. Subgaleal abscess formation without an overlying wound or previous trauma has not been reported previously.

S UBGALEAL ABSCESSES AND OSTEOMYELITIS OF' THE SI<ULL are rarely encountered today (1).Recent reports of these entities usually describe an underlying pathology such as trauma or puncture wounds which account for direct inoculation or contiO"uous spread of microorganisms (2-ll).Although the diagnosis and management of a secondary subgaleal abscess may be straightforward, the same cannot be said for a p1imruy or de novo subgaleal abscess.The authors report a case of a patient who developed a de novo subgaleal abscess and secondary osteomyelitis.

CASE PRESENTATION
A 62-year-old female was referred to the neurosurgical service at University Hospital complaining of painful fluctuant swellings of the scalp.She had been well until six weeks prior to admission .when she experienced symptoms of an upper respiratory tract infection with dysphonia.mild fever and malaise, for which symptomatic relief was obtained with acetylsalicylic acid tablets.Two days afi.er the upper respiratory infection had subsided.the patient noted pain of moderate intensity in the occipital area with radiation towru•d the frontal regions of the skull.Within days the entire scalp had become swollen and markedly painful.There was no history of antecedent them1al, chemical or mechanical trauma.Past medical history included hypertension controlled with thiazide diuretics and an appendectomy performed many years previously.There was no suggestion of sinusitis.diabetes or any immunological disorder.Other than swelling over the scalp and lenderness to palpation, examination was normal.
The patient was admitted to a local hospital.where sku ll radiographs and computed tomography scan revealed only soft tissue swelling over the calvarium .No evidence of mucosal thickening or opacification of the sinuses was apparent.Although the alkaline phosphatase level was elevated at 180 U/L (normal 30 to 85). a techneti urn bone scan did not reveal any evidence of o teomyelitis.An incision was made into U1e subgalea!space and 180 mL of purulent material was drained.A small drain was left in this incision for approximately one week.This exudate contained many Gram-positive cocci and pus cells, and culture revealed a pure growth of Streptococcus pyogenes.The patient was treated initially with parenteral cefazolin 1 g every 8 h for 21 days.and after some improvement was changed to oral cephalexi.nfor a further seven days.However. the swelling did not resolve.and she was subsequently transferred to the authors• institution for further assessment.
Examination revealed three painful fluctuant swellings each measuring approximately 2 em in diameter over the occipital.left parietal and frontal areas of the skull.Other physical findings included moderate alopecia and palpable posterior cervical lymph nodes .Ophthalmoscopy and otoscopy were unremarkable.There was no meningismus.Complete neurological examination was unremarkable.A complete blood count revealed a hemoglobin of 103 g/L. a white blood cell count of 11.4xl0 9 /L (81 % neutrophils, 13% lymphocytes and 6% monocytes).a packed cell volume of0.3l.and an e1ythrocyte count of 3 .2x10 9/L.The erythrocyte seclin1entation rate was 76 mm/h.The streptozyme (F Homer Inc) titre was 1:1000.A technetium bone scan indicated an area of increased uptake over the left parietal bone, suggesting a focus of osteomyelitis.
Treatment was started with intravenous penicillin G three million units every 4 h.and the patient was tal\:en to the operating room for incision and debridement.A sagittal incision about 15 em in length was made and tile subgaleal space widely explored .The galea aponeurotica was found to be extensively necrotic.All necrotic tissue was excised.Gross inspection revealed no apparent abnormalities of tile bone.The wound was closed and two Penrose drains were brought out through separate stab incisions on each side.The drains were shorten ed and removed in five days.Microscopic examination of tile bone curettings revealed num rous neutrophils witll occasional intracellulru• Gram -positive cocci.Culture of lhe debrided material bot11 aerobically and anaerobically revealed no growt11.
Based on the clinical and laboratmy findings.a diagnosis of subgaleal abscess and osteomyelitis of the parietal bone secondary to Strep pyogenes was made.The patient was treated witll intravenous penicillin G for a total of six weeks.and has remained well after six mont11s of follow-up.

DISCUSSION
Infections of the scalp may involve any of tile tissue layers s uperficia l to the calvruium (skin.subcutaneous tissue.aponeurosis, loose connective tissue or periosteum).and although most are minor and limited.they can progress to involve t11e deeper layers.Subgaleal abscesses ru•e purulent infections deep to the galea aponeurotica (aponeurosis epicrruualis) of the scalp.The subgaleal space.which is a potential anatomical space beneath llie galea aponeurotica.extends from tile supraorbital ridge ru1teriorly.to the cervical muscles posteriorly, and to the auricular muscles laterally.Loose connective tissue carrying emissary veins from the dural sinuses to tile superficial scalp veins binds the galea to llie per•iosteum of the skull.
The de novo appearance of a subgaleal abscess has not been reported previously.On direct questioning.the present patient did not have any antecedent trauma or disruption of the scalp prior to infection, and there was no evidence of immunological compromise based on clinical examination and laboratory findings.The infection likely occurred due to hematogenous spread .related to the upper respiratory infection which occurred just prior to the onset of scalp swelling.The diagnosis of subgaleal abscess in the present patient was based mainly on clinical findings and aspiration and culture of exudate from the subgaleal space.Plain radiography, computed tomography and technetium-99 methylene diphosphonate bone scanning were useful adjuncts in making an anatomical diagnosis.The bone scan suggested an underlying osteomyelitis which was subsequently confirmed upon microscopy.The course of t11e present patient's infection was monitored clinically and was uneventful.The failure to respond to initial treatment was Ukely due to inadequate debridement and drainage.the unrecognized presence of osteo-Osteomyelilis of lhe skull following scalp reducUon and hair plug transplantation.Ann Plast Surg 1980:5:480-2.
The predominant organism isolated from post traumatic and post surgical scalp infections is Staphy lococcus aureus (ll).However, other organisms such as Strep pyogenes (9) and Eilcenella corrodens (5) have b een reported.In the neonatal age group. in wh ich a bscess formation can be a complication of fetal scalp electrode monitoring, Staphylococcus epidennidis accounted for 58% of positive cultures in one review (8).Polymicrobial infections may also occur \>vith ilie presence of anaerobes in association \>villi either Staph aureus or Strep pyogenes (2).
The preferred surgical treatment of subgaleal abscess is incision, meticulous debridement and drainage (1.2,11).although repeated needle aspirations may occasionally be successful (10).Purulent exudate or debrided tissue should be sent for immediate Gram smear and cu ltured botl1 aerobically and anaerobically.Parenteral antimicrobial U1erapy is a dministered for one to three weeks.followed by a ppropriate oral t11erapy.Indwelling drains are often required.If a complication such as osteomyelitis is present.more prolonged t11erapy is required .
CAN J INFECT DIS VOL 3 No 1 J ANUARY / FEBRUARY 1992 De novo subgaleal abscess