Discussion

Only a handful of case reports have described about the frontal sinus osteomyelitis following mucormycosis8–11. Mucormycosis usually affects the nose and paranasal sinuses; the disease can spread via direct extension or by hematogenous spread. Hossieni and colleagues12 initially have described about the routes of spread of mucormycosis. We hypothesize the following pathway for the spread of mucormycosis into the frontal sinus –
  1. Via the ethmoidal air cells by direct extension, leading to frontal outflow tract obstruction.
  2. By erosion of frontal sinus floor from superior part of the orbit.
  3. Perineural spread along the supraorbital or supratrochlear nerves.
  4. Along the anterior ethmoidal arteries.
  5. Direct spread to the brain through the roof of the ethmoid and cribriform plate to skull base/frontal bone to Basi frontal lobe.
  6. Disease tracking along the Orbital apex.
In acute osteomyelitis, the patient is toxic with tender swelling over the bone involved, called Pott’s puffy tumour. The Pott’s puffy tumour was initially described as complication of acute bacterial frontal sinusitis. The successful management of frontal bone osteomyelitis entails removal of the entire sequestrum and debriding the involucrum till the normal bony architecture is reached. Frontal sinus obliteration with the fat, muscle and alloplastic materials have been tried with varying success. In the setting of mucormycosis, it is utmost important to clear all the disease till the fresh bleeding is observed. The main crux of frontal sinus cranialization or obliteration in the mucormycosis setting is to ensure complete elimination of disease and dead space, formation of a protective barrier for the intracranial spread and with the ability to reassess clincoradiologically for disease recurrence. The use of alloplastic materials is usually not recommended in the settings of severe infection13.
The disease is more susceptible to complete endoscopic surgical resection along with bony debridement if detected early14. Because antifungal medication alone will not suffice, all grossly diseased tissue must be excised. Debridement should be repeated until a healthy tissue margin is found, and it should be done at regular intervals, if necessary. Sinus surgery, wide resection of necrotic soft tissue and bone, and exenteration of the orbit, if necessary, are examples of more comprehensive surgical treatments15,16. According to the available literature, patients with intracranial extension are less likely to react to radical surgery, and their prognosis is poor17. However, if surgery is done early on, the chances of survival increase significantly14. It is well established that the management of comorbid conditions is crucial in the successful management of mucormycosis. It is also the single most crucial factor determining the overall prognosis of the patient18.
As per the AMBILOAD trial19, higher dose preparations of amphotericin B does not improve the overall outcome compared to the conventional dosing. Before amphotericin B dosage, factors such as existing diabetic and hypertension-induced nephropathy must be kept in mind. There is no strict consensus on the duration and the target dosage of amphotericin B therapy20, especially in the recurrent setting. Based on our institutional expert multidisciplinary team recommendations, we have titrated the target dose based on the extent of the disease, comorbidities, and response to therapy.
The overall better outcomes in this study can be attributed to the early detection, prompt surgical debridement, prolonged amphotericin B and strict management of comorbidities, In a recent systematic review, 80% mortality was seen with CNS involvement21; Among the patients who have survived the CNS, debridement has the minimal or early invasion of the dura and brain.
Long term outcomes of fungal osteomyelitis of frontal bone are not well established.